PhysicsPhysics QuestionsElectromagnetic Induction Questions for CBSE Class 12th

Electromagnetic Induction Questions for CBSE Class 12th

  1. If a current of 10 A flows in one second through a coil, and the induced e.m.f. is 10 V, then the self-inductance of the coil is
  2. The magnetic flux ϕ linked with a pure inductor varies with the current (i) flowing through it according to the graph shown in figure. If the current increases at a constant rate of 2 A/s, find the potential difference across the inductor.
  3. The north and south poles of two identical magnets approach a coil, containing a condenser, with equal speeds from opposite sides. Then
  4. A wire is bent to form the double loop shown in figure. There is a uniform magnetic field directed into the plane of the loop. If the magnitude of this field is decreasing, the current will flow from
  5. A ring of mass m, radius R having charge q uniformly distributed over it and free to rotate about its own axis is placed in a region having a magnetic field B parallel to its axis. If the magnetic field is suddenly switched off, the angular velocity acquired by the ring is
  6. A wire of fixed length is wound in such a way that it forms a solenoid of length ‘l’ and radius ‘r’. Its self-inductance is found to be Z. Now if same wire is wound in such a way that it forms a solenoid of length I /2 and radius r /2, then the self-inductance will be
  7. A conducting rod of length L is falling with velocity v perpendicular to a uniform horizontal magnetic field B; the potential difference between its two ends will be :
  8. A copper disc of radius 10 cm is rotating in magnetic field B = 0.4 gauss with 10 rev./sec. What will be potential difference across peripheral points of disc?
  9. In the circuit shown, switch is connected to position 1 for a very long time. What is maximum current through inductor when switch is taken to position 2?
  10. In the circuit shown in figure, the switch S is closed at t = 0, when reading of the voltmeter is 8 volt, the energy stored in the inductor is [Given R = 4 Ω   and   L = 10   mH ]
  11. The magnetic flux linked with a coil at any instant t is given by ϕ = 5 t 3 − 100 t + 300 , the e.m.f. induced in the coil at t = 2 s is
  12. A coil of area 100 cm 2 has 500 turns. Magnetic field of 0.1 weber/metre 2 is perpendicular to the coil. The field is reduced to zero in 0.1 second. The induced e.m.f. in the coil is
  13. An aeroplane in which the distance between the tips of wings is 50 m is flying horizontally with a speed of 360 km/hr over a place where the vertical components of earth magnetic field is 2 .0 × 10 − 4 weber / m 2 . The potential difference between the tips of wings would be
  14. A varying current at the rate of 3 A/s in a coil generates an e.m.f. of 8 mV in a nearby coil. The mutual inductance of the two coils is
  15. When the current in a coil changes from 8 amperes to 2 amperes in 3 x 10 -2 second, the e.m.f. induced in the coil is 2 volt. The self-inductance of the coil, in milli-henry is
  16. A long solenoid of length L, cross-section A having N 1 tums has wound about its centre is small coil of N 2 turns as shown in fig.(10). Then the mutual inductance of two circuits is
  17. A cycle wheel of radius 0.5 m is rotated with constant angular velocity of 10 rad/s in a region of magnetic field of 0.1 T which is perpendicular to the plane of the wheel. The EMF generated between its centre and the rim is,
  18. A circular coil of radius 10 cm, 500 turns and resistance 2 Ω is placed with its plane, perpendicular to the horizontal component of the earth’s magnetic field. It is rotated about its vertical diameter through 180° in 0.25 s. The induced e.m.f. in the coil is ( T a k e H E = 3 . 0 x 10 – 5 T ) :
  19. A wire of fixed length is wound on a solenoid of length l and radius r. Its self inductance is found to be L. Now if same wire is wound on a solenoid of length l 2 and radius r 2 then its self-inductance will be
  20. A rod lies across frictionless rails in a uniform magnetic field as shown in Fig. The rod moves to the right with speed V. In order to make the induced emf in the circuit to be zero, the magnitude of the magnetic field should
  21. At time t = 0 magnetic field of 1000 Gauss is passing perpendicularly through the area defined by the closed loop shown in the figure. If the magnetic field reduces linearly to 500 Gauss, in the next 5s, then induced EMF in the loop is:
  22. A thin copper rod ABC is bent at point B as shown in figure. The bent rod is rotating with angular velocity ω = 10   r a d / s about an axis passing through A and perpendicular to the plane of the bent rod. There is a uniform magnetic field of induction B = 0.5 T perpendicular to the plane of the page then induced potential difference between end C and point B is
  23. A and B are two metallic rings placed at opposite sides of an infinitely long straight conducting wire as shown in figure. If current in the wire is slowly decreased, the direction of the induced current will be
  24. The graph shows the variation in magnetic flux ϕ ( t ) with time through a coil. Which of the statements given below is not correct?
  25. A rectangular loop with a sliding connector of length l =1.0 m is situated in a uniform magnetic field B = 2T perpendicular to the plane of loop. Resistance of connector is r=2 Ω . Two resistance of 6 Ω and 3 Ω are connected as shown in figure. The external force required to keep the connector moving with a constant velocity v = 2 m/s is
  26. A conducting rod PO of length l = 2 m is moving at a speed of 2 ms -1 making an angle of 30 o with its length. A uniform magnetic field B = 2T exists in a direction perpendicular to the plane of motion. Then
  27. Figure shows a square loop of side 0.5 m and resistance 10 Ω . The magnetic field has a magnitude B = 1.0 T. The work done in pulling the loop out of the field slowly and uniformly in 2.0 s is
  28. A vertical conducting ring of radius R falls vertically with a speed V in a horizontal uniform magnetic field B which is perpendicular to the plane of the ring. Which of the following statements is correct
  29. Figure shows three regions of magnetic field each of area A, and in each region, magnitude of magnetic field decreases at a constant rate α .It E is the induced electric field, then the value of the line integral ∮ E ⋅ d r along the given loop is equal to
  30. A long solenoid having 200 turns per centimeter carries a current of 1.5 A. At the center of the solenoid is placed a coil of 100 turns of cross-sectional area 3.14 x 10 -4 m 2 having its axis parallel to the field produced by the solenoid. When the direction of current in the solenoid is reversed within 0.05 s, the induced emf in the coil is
  31. A wire of length l , mass m, and resistance R slides without any friction down the parallel conducting rails of negligible resistance (figure). The rails are connected to each other at the bottom by a resistanceless rail parallel to the wire so that the wire and the rails form a closed rectangular conducting loop. The plane of the rails makes an angle θ with the horizontal and a uniform vertical magnetic field of induction B exists throughout the region. Find the steady state velocity of the wire.
  32. A small piece of metal wire is dragged across the gap between the poles of a magnet in 0.4 sec. If the change in magnetic flux is 8 x 10 -4 Wb, emf induced in the wire is :
  33. A long solenoid of diameter 0.1 m has 2 x 10 4 turns per meter. At the centre of the solenoid, a coil of 100 turns and radius 0.0 I m is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to OA from 4A in 0.05 s. If the resistance of the coil is 10 π 2 Ω . The total charge flowing through the coil during this time is :
  34. A rod PQ of mass ‘m’ and resistance ‘r’ is moving on two fixed, resistance less, smooth conducting rails (closed on both sides by resistance R 1 and R 2 ). Then the current in the rod at the instant when its velocity V is (A uniform magnetic field B exists in the region)
  35. A metallic ring is rotating with uniform angular velocity about its diameter in a uniform magnetic field. Then emf induced in the ring is
  36. A coil of 40 Ω resistance having 100 turns and radius 6 mm is connected to an ammeter of resistance of 160 ohms. Coil is placed perpendicular to the magnetic field. When coil is taken out of the field, 32   μ C charge flows through it. The intensity of magnetic field will be
  37. The inductance of a coil is 60 μH . A current in this coil increases from 1.0 A to 1.5 A in 0.1 s. The magnitude of the induced e.m.f. is
  38. The average e.m.f. induced in a coil in which a current changes from 0 to 2 A in 0.05 s is 8 V. The self-inductance of the coil is
  39. The mutual inductance between two coils is 1.25 H. If the current in the primary changes at the rate of 80 amperes/second, then the induced e.m.f. in the secondary is
  40. A rectangular coil ABCD is rotated anticlockwise with a uniform angular velocity about the axis shown in diagram below. The axis of rotation of the coil as well as the magnetic field B are horizontal. The induced e.m.f. in the coil would be maximum when
  41. A conducting rod AC of length 4 l is rotated about a point O in a uniform magnetic field B directed into the paper. AO = l and OC = 3 l . Then
  42. A circular coil of mean radius of 7 cm and having 4000 turns is rotated at the rate of 1800 revolutions per minute in the earth’s magnetic field (B = 0.5 gauss). The maximum e.m.f. induced in coil will be
  43. A straight wire of length L is bent into a semicircle. It is moved in a uniform magnetic field with speed v with diameter perpendicular to the field. The induced emf between the ends of the wire is
  44. The current in a coil of inductance 5 H decreases at the rate of 2 A/s. The induced e.m.f. is
  45. A circular coil of radius 5 cm has 500 turns of a wire. The approximate value of the coefficient of self-induction of the coil will be
  46. The inductance of a closed-packed coil of 400 turns is 8 mH. A current of 5 mA is passed through it. The magnetic flux through each turn of the coil is
  47. The resistance and inductance of series circuit are 5 Ω and 20 H, respectively. At the instant of closing the switch, the current is increasing at the rate 4 A/s. The supply voltage is
  48. The mutual inductance of an induction coil is 5H. In the primary coil, the current reduces from 5A to zero in 10 – 3 s . What is the induced e.m.f. in the secondary coil?
  49. If the current is halved in a coil, then the energy stored is how much times the previous value?
  50. In an LR circuit, time constant is that time in which current grows from zero to the value (where I 0 is the steady state current)
  51. A long solenoid of length l, cross-section A having N 1 turns has wound about its centre a small coil of N 2 turns as shown in figure Then the mutual inductance of two circuits is
  52. The network shown in the figure is a part of a complete circuit. If at a certain instant the current i is 5 A and is decreasing at the rate of 10 3 A / s then V B – V A is
  53. Pure inductance of 3.0 H is connected as shown below. The equivalent inductance of the circuit is
  54. In an LR circuit, time constant is that time in which current grows from zero to the value (where I 0 is the steady state current)
  55. In the given sub circuit, the resistance R = 0 . 2 Ω If V A – V B = 0 . 5 V I = 0.5 A and (dI/dt) = 8 A/s, then find the inductance of the coil.
  56. An inductance L and a resistance R are first connected to a battery. After some time the battery is disconnected but L and R remain connected in a closed circuit. Then the current reduces to 37% of its initial value in time
  57. The figure shows three circuits with identical batteries, inductors, and resistors. Rank the circuits according to the current through the battery (i) just after the switch is closed and (ii) a long time later, greatest first. [i 1 , i 2 and i 3 are respective current in circuit (1), (2) and, (3)]
  58. Statement 1: Self-inductance is called the inertia of electricity. Statement 2: Self-inductance is the phenomenon, according to which an opposing induced e.m.f. is produced in a coil as a result of change in current or magnetic flux linked in the coil.
  59. Find out the e.m.f. produced when the current changes from 0 to 1 A in 10 s, given L = 10 mH.
  60. A flat circular coil 10 cm radius has 200 turns. The coil is connected to a capacitor of capacity 20 μ F. It is placed in a uniform magnetic field which decreases at a rate of 0.01 tesla per second. The charge (in μ C ) on the capacitor is .
  61. Two identical inductance carry currents that vary with time according to linear laws (as shown in figure). In which of two inductance is the self induced emf greater?
  62. Two concentric coplanar circular loops made of wire with resistance per unit length 10 − 4 Ω / m , have diameters 0.2 m and 2 m. A time varying potential difference (4 + 2.5t) volt is applied to the larger loop. The current (in A) in the smaller loop is .
  63. A cylindrical bar magnet is kept along the axis of a circular coil. If the magnet is rotated about its axis, then
  64. In a coil of area 10 cm 2 and 10 turns with a magnetic field directed perpendicular to the plane and is changing at the rate of 10 8 gauss/second. The resistance of the coil is 20 ohm. The current in the coil will be
  65. A 50 turns circular coil has a radius of 3 cm, it is kept in a magnetic field acting normal to the area of the coil. The magnetic field B increased from 0.10 tesla to 0.35 tesla in 2 milliseconds. The average induced e.m.f. in the coil is
  66. The north pole of a bar magnet is moved swiftly downward towards a closed coil and then second time it is raised upwards slowly. The magnitude and direction of the induced currents in the two cases will be of
  67. A magnetic field of 2 × 10 – 2 T acts at right angles to a coil of area 100 cm 2 with 50 turns. The average emf induced in the coil is 0.1 V, when it is removed from the field in time t. The value of t is
  68. The north pole of a magnet is brought near a metallic ring. The direction of the induced current in the ring will be
  69. A solenoid is 1.5 m long and its inner diameter is 4.0 cm. It has three layers of windings of 1000 turns each and carries a current of 2.0 amperes. The magnetic flux for a cross-section of the solenoid is nearly
  70. A moving conductor coil in a magnetic field produces an induced e.m.f. This is in accordance with
  71. Lenz’s law applies to
  72. When a bar magnet falls through a long hollow metal cylinder fixed with its axis vertical, the final acceleration of the magnet is
  73. The magnetic flux linked with a circuit of resistance 100 ohm increases from 10 to 60 webers. The amount of induced charge that flows in the circuit is (in coulomb)
  74. An infinitely long cylinder is kept parallel to an uniform magnetic field B directed along positive z axis. The direction of induced current as seen from the z axis will be
  75. Average energy stored in a pure inductance L when a current i flows through it, is
  76. When the current in a coil changes from 8 ampere to 2 ampere in 3 × 10 − 2 second, the e.m.f. induced in the coil is 2   volt . The self inductance of the coil (in millihenry) is
  77. The energy stored in a 50 mH inductor carrying a current of 4 A will be
  78. The inductance of a closed-packed coil of 400 turns is 8 mH. A current of 5 mA is passed through it. The magnetic flux through each turn of the coil is
  79. A coil of resistance 10 Ω and an inductance 5H is connected to a 100 volt battery. Then energy stored in the coil is
  80. An air core solenoid has 1000 turns and is one metre long. Its cross-sectional area is 10 cm 2 . Its self inductance is
  81. The current through choke coil increases form zero to 6A in 0.3 seconds and an induced e.m.f. of 30 V is produced. The inductance of the coil of choke is
  82. Why the current does not rise immediately in a circuit containing inductance?
  83. Two identical induction coils each of inductance L joined in series are placed very close to each other such that the winding direction of one is exactly opposite to that of the other, what is the net inductance
  84. In the figure magnetic energy stored in the coil is
  85. Use of eddy currents is done in the following except
  86. Which of the following is constructed on the principle of electromagnetic induction
  87. Eddy currents are produced when
  88. If rotational velocity of a dynamo armature is doubled, then induced e.m.f. will become
  89. An electric motor operates on a 50 volt supply and a current of 12A. If the efficiency of the motor is 30%, what is the resistance of the winding of the motor?
  90. In a dc motor, induced e.m.f. will be maximum
  91. A thin semicircular conducting ring of radius R is falling with its plane vertical in a horizontal magnetic induction B. At the position MNQ, the speed of the ring is V and the potential difference developed across the ring is
  92. In the following figure, the magnet is moved towards the coil with a speed v and induced emf is e. If magnet and coil recede away from one another each moving with speed v, the induced emf in the coil will be
  93. A current carrying solenoid is approaching a conducting loop as shown in the figure. The direction of induced current as observed by an observer on the other side of the loop will be
  94. The north and south poles of two identical magnets approach a coil, containing a condenser, with equal speeds from opposite sides. Then
  95. The network shown in the figure is a part of a complete circuit. If at a certain instant the current i is 5 A and is decreasing at the rate of 10 3 A / s then V A − V B is
  96. An induction coil stores 32 joules of magnetic energy and dissipates energy as heat at the rate of 320 watt when a current of 4 amp is passed through it. Find the time constant of the circuit when the coil is joined across a battery.
  97. A magnetising field of 1600 A/m produces a magnetic flux of 2.4 x 10 – 5 Weber in an iron bar of cross section 0.2 cm 2 . Permeability of the bar is
  98. In which of the following devices, the eddy current effect is not used?
  99. The magnetic flux ϕ (in Weber) in a closed circuit of resistance 10 Ω varies with time t (in second) according to equation ϕ = 6 t 2 − 5 t + 1 . The magnitude of induced current at t = 0.25sec is
  100. The mutual inductance between two planar concentric rings of radii r 1 and r 2 (with r 1 > r 2 ) placed in air is given by
  101. A thin copper rod of length 1.5 m lies in xy plane parallel to y-axis. It starts moving with a constant velocity V = 3 i ^ + 4 j ^ m / s . A uniform magnetic field B = i ^ − j ^ + k ^ T exists in that region. Then induced potential difference between the ends of the rod is
  102. Induction of a solenoid is 15 mH. Now length of the solenoid is halved, number of turns doubled and area of cross section remains the same. Then the new inductance of the solenoid will be
  103. A thin metallic ring of radius 5 cm is made of a wire of resistance 2   Ω m . The ring is placed in a uniform magnetic field of induction 1 Tesla with its plane perpendicular to the field. Now the ring starts rotating with angular velocity ω = 10   r a d / sec ⁡ . Then rms value of current induced in the ring is
  104. A thin copper rod AB of length l is rotating with constant angular velocity about an axis passing through the end A and perpendicular to the plane of page in a uniform magnetic field of induction B as shown in the figure. P and Q are two points on the rod such that A P = l 4 and A Q = l 2 . If ‘V’ is the induced potential at a point on the rod, then V Q − V P / V B − V A    i s
  105. A proton is at rest at point P. There is a magnetic field on induction B directed along negative Z-axis. If B gradually increases
  106. A circular coil of radius 10cm is placed in a uniform magnetic field of 3.0 × 10 − 5 T with its plane perpendicular to the field initially. It is rotated at constant angular speed about an axis along the diameter of coil and perpendicular to magnetic field so that it undergoes half of rotation in 0.2s. The maximum value of EMF induced in μ V in the coil will be close to the integer
  107. A current carrying solenoid is approaching a conducting loop as shown in the figure. The direction of induced current as observed by an observer on the other side of the loop will be
  108. A plane loop, shaped as two squares of sides a = 1 m and b =0.4 m is introduced into a uniform magnetic field ⊥ to the plane of loop (figure). The magnetic field varies as B=10 -3 sin(100t) T. The amplitude of the current induced in the loop if its resistance per unit length is r = 5 mΩm − 1 is
  109. Three identical coils A, B, and C carrying currents are placed coaxially with their planes parallel to one another. A and C carry currents as shown in figure. B is kept fixed, while A and C both are moved toward B with the same speed. Initially, B is equally separated from A and C. The direction of the induced current in the coil B is
  110. A flexible wire bent in the form of a circle is placed in a uniform magnetic field perpendicularly to the plane of the coil. The radius of the coil changes as shown in figure. The graph of magnitude of induced emf in the coil is represented by
  111. A right angled triangular loop (as shown in the figure) enters into uniform magnetic field (at right angle to the boundary of the field) directed into the paper. The loop moves always with constant speed. Draw the graph between induced emf e and the distance along the perpendicular to the boundary of the field (say x) along which loop moves.
  112. A square coil ACDE with its plane vertical is released from rest in a horizontal uniform magnetic field E of length 2L (figure). The acceleration of the coil is
  113. A rod PQ is connected to the capacitor plates. The rod is placed in a magnetic field (B) directed downward perpendicular to the plane of the paper. If the rod is pulled out of magnetic field with velocity v as shown in figure,
  114. Figure shows a copper rod moving with velocity v parallel to a long straight wire carrying current = 100 A. Calculate the induced emf in the rod, where v= 5 m s -1 , a= 1 cm, b = 100 cm
  115. A metallic ring of radius r with a uniform metallic spoke of negligible mass and length r is rotated about its axis with angular velocity ω in a perpendicular uniform magnetic field B as shown in figure. The central end of the spoke is connected to the rim of the wheel through a resistor R as shown. The resistor does not rotate, its one end is always at the center of the ring and the other end is always in contact with the ring. A force F as shown is needed to maintain constant angular velocity of the wheel. F is equal to (the ring and the spoke has zero resistance)
  116. A square non-conducting loop, 20 cm, on a side is placed in a magnetic field. The center of side AB coincides with the center of magnetic field. The magnetic field is increasing at the rate of 2 T/s. The potential difference between C and D is
  117. A thin non-conducting ring of mass m carrying a charge Q can freely rotate about its axis. Initially, the ring is rest and no magnetic field is present. Then a uniform field of magnetic induction was switched on, which was perpendicular to the plane of the ring and increased with time as a given function B(t). The angular velocity ω (t) of the ring as a function of the field B(t) will be given by
  118. In the circuit shown ln figure, a conducting wire HE is moved with constant a speed v toward left. the complete circuit is placed in a uniform magnetic field B perpendicular to the plane of the circuit inward. The current in HKDE is
  119. An emf of 96.0 mV is induced in the windings of a coil when the current in a nearby coil is increasing at the rate of 1 .20 A/s The mutual inductance of the two coils is
  120. Two single-turn circular loops of wire have radii R and r, with R >> r. The loops lie in the same plane and are concentric. The mutual inductance of the pair is (approximately)
  121. A closed loop of cross-sectional area 10 -2 m 2 which has inductance L = 10 mH and negligible resistance is placed in a time-varying magnetic field. Figure shows the variation of B with time for the interval 4 s. The field is perpendicular to the plane of the loop (given at t = 0, B = 0,I = 0). The value of the maximum current induced in the loop is
  122. Flux ϕ (in weber) in a closed-circuit of resistance 10 ohm varies with time t (in sec) according to the equation : ϕ = 6 t 2 – 5 t + 1 What is the magnitude of the induced current at t = 0.25 s ?
  123. The magnetic field of 2 x 10 -2 tesla acts at right-angles to a coil of area 100 cm 2 with 50 turns. The average emf induced in the coil is 0.1 V when it is removed from the field in time t. The value of t is :
  124. A cylindrical bar magnet is kept along the axis of a circular coil. If the magnet is rotated about its axis, then :
  125. The magnetic flux linked with the coil varies with time as ϕ = 3 t 2 + 4 t + 9 . The magnitude of the induced emf at 2 s is :
  126. If the radius of a coil is changing at the rate 10 -2 units in a normal magnetic field 10 -3 units, the induced emf is 1 μV. What is the final radius of the coil ?
  127. A circular disc of radius 0.2 metre is placed in a uniform magnetic field of induction 1 π Wb m 2 in such a way that its axis makes an angle of 60° with B. The magnetic flux linked with the disc is :
  128. A conducting circular loop is placed in a uniform magnetic field, B = 0.025 T with its plane perpendicular to the loop. The radius of the loop is made to shrink at a constant rate of 1 mm/s. The induced emf when the radius is 2 cm, is :
  129. A thin semicircular conducting ring (PQR) of radius ‘r’ is falling with its plane vertical in a horizontal magnetic field B, as shown in figure. The potential difference developed across the ring when its speed is v, is :
  130. A body enters in MRI machine in 10 sec. If the magnetic field is 1.5 T and circumference of MRI machine is 0.9 m then find out emf induced in the body.
  131. A person is laying down in a MRI machine. Circumference of person is 0.8 m. If change in magnetic field is 2T per 10 second, find induced emf in the person.
  132. Two coils have a mutual inductance 0.005 H. The current changes in first coil according to equation I = I 0 sin wt where I 0 = 2 A and ω = 100 π rad/sec. The maximum value of emf in second coil is :
  133. When the current changes from + 2 A to – 2A in 0.05 s, an emf of 8 V is induced in a coil. The coefficient of self-induction of the coil is :
  134. The time constant of a circuit is 10 sec, when a resistance of 10 Ω is connected in series in a previous circuit then time constant becomes 2 second, then the self inductance of the circuit is :
  135. A capacitor of capacitance C = 0.015F is connected to parallel conducting rail and a conducting rod of mass m = 100g and length l = 1 m start to fall under gravity in vertical plane. A uniform magnetic field of 2 T exist in space directed perpendicular to rod as shown in figure. Find acceleration of rod.
  136. In a region, there exist a uniform magnetic field B 0 along positive x-axis . A metallic wire of length 2a and one side along x-axis and one side parallel to y-axis is rotating about y-axis with an angular velocity ω . Then at the instant shown, magnitude of induced electro motive force between P  and  R is
  137. Magnetic flux linked with a closed circuit of resistance 10 Ω is given by ϕ = 5 t 2 – 4 t + 1 weber, when t is time in second. Then induced electric current at t = 0 is
  138. A circular coil having an area of 3.14 × 10 -2 m 2 and 30 turns is rotated about its vertical diameter with an angular speed of 70 rad -1 in a uniform horizontal magnetic field of magnitude 5 × 10 -2 T. If the coil forms a closed loop of resistance 15 Ω, what is the average power loss due to Joule heating?
  139. A conducting square frame of side ‘a’ and a long straight wire carrying current I are located in the same plane as shown in the figure. The frame moves to the right with a constant velocity ‘V’. The emf induced in the frame will be proportional to :
  140. Two circular, and similar coaxial loops carry equal currents in the same direction. If the loops are brought nearer, what will happen?
  141. Two circular, and similar coaxial loops carry equal currents in the same direction. If the loops are brought nearer, what will happen?
  142. A metallic ring connected to a rod oscillates freely like a pendulum. If now a magnetic field is applied in horizontal direction (as shown) so that the pendulum now swings through the field, the pendulum will
  143. As shown in the figure, a magnet is moved with fast speed towards a coil at rest. Due to this induced electromotive force, induced current and induced charge in the coil is E, I and Q, respectively. If the speed of the magnet is doubled, then find the incorrect option from the following.
  144. A square coil ABCD is lying in an x-y plane with its centre at origin. A long straight wire passing through origin carries a current i = 2t in negative z-direction. The induced current in the coil is
  145. If a coil of 40 turns and area 4 cm 2 is suddenly removed from a magnetic field, it is observed that a charge of 2.0 × 10 − 4 C flows into the coil. If the resistance of the coil is 80   Ω , the magnetic flux density in Wb/m 2 is
  146. A flexible wire bent in the form of a circle is placed in a uniform magnetic field perpendicular to the plane of the coil. The radius of the coil changes as shown in figure. The graph of induced emf in the coil is represented by
  147. If a conductor of 3 m in length is moving perpendicularly to magnetic field of 10 – 3 tesla with the speed of 10 2 m/s, then the e.m.f. produced across the ends of conductor will be
  148. At a place the value of horizontal component of the earth’s magnetic field is 3 × 10 – 5 Wb / m 2 . A metallic rod AB of length 2 m placed in east-west direction, having the end A towards east, falls vertically downward with a constant velocity of 50 m/s. Which end of the rod becomes positively charged and what is the value of induced potential difference between the two ends?
  149. When the current in a coil changes from 8 A to 2 A in 3 × 10 – 2 s the e.m.f. induced in the coil is 2 volt. The self-inductance of the coil (in millihenry) is
  150. After how much time energy becomes 1 e of the maximum value in a R-L circuit where R = 2 Ω and L = 2mH?
  151. When the number of turns and the length of the solenoid are doubled keeping the area of cross-section same, the inductance
  152. The current through choke coil increases from zero to 6 A in 0.3 seconds and an induced e.m.f. of 30 V is produced. The inductance of the coil of choke is
  153. If a current of 3.0 amperes flowing in the primary coil is reduced to zero in 0.001 second, then the induced e.m.f. in the secondary coil is 15000 volts. The mutual inductance between the two coils is
  154. The inductance of a solenoid, 0.5 m long of cross-sectional area 20 cm 2 and with 500 turns, is
  155. The inductance between A and D is :
  156. Two inductance coils of inductances L 1 and L 2 are kept at sufficiently large distance apart. On connecting them in parallel their equivalent inductance will be :
  157. A long solenoid has 500 turns. When a current of 2 A is passed through it, the resulting magnetic flux linked with each the turn of the solenoid is 4 × 10 − 3 Wb . The self-inductance of the solenoid is
  158. In a transformer, the coefficient of mutual inductance between the primary and the secondary coil is 0.2 H. When the current changes by 5 A/s in the primary the induced e.m.f. in the secondary will be
  159. Figure shows a square loop of side 0.5 m and resistance 10 Ω . The magnetic field has a magnitude B = 1.0 T. The work done in pulling the loop out of the field slowly and uniformly in 2.0 s is
  160. Two coils have a mutual inductance 0.005 H. The current changes in the first coil according to equation I = I 0 sin ω t , where I 0 = 10 A and ω = 100 π radian / s The maximum value of e.m.f. in the second coil is
  161. Switch s of the circuit, shown in figure, is closed at t = 0. If e denotes the induced emf in L and i, the current flowing through the circuit at time t, which of the following graphs is correct?
  162. A coil of wire having finite inductance and resistance has a conducting ring placed coaxially within it. The coil is connected to a battery at time t = 0, so that a time-dependent current I 1 (t) starts flowing through the coil. If I 2 (t) is the current induced in the ring and B(t) is the magnetic field at the axis of the coil due to I 1 (t) then as a function of time (t > 0), the product I 2 (t) B(t)
  163. The current carrying wire and the rod AB are in the same plane. The rod moves parallel to the wire with a velocity v. Which one of the following statements is true about induced e.m.f. in the rod?
  164. The average e.m.f. induced in a coil in which the current changes from 2 amperes to 4 amperes in 0.05 seconds is 8 volts. What is the self-inductance of the coil?
  165. The approximate formula expressing the inductance of two thin co-axial loops of the same radius a when their centres are separated by a distance l with l > > a is
  166. In the circuit shown below, the key K is closed at t = 0. The current through the battery is :
  167. An e.m.f. of 15 v is applied in a circuit containing 5 H inductance and 10 Ω resistance. The ratio of the currents at time t = ∞ and at t = 1 s is
  168. Two circuits have mutual inductance of 0.1 H. What average e.m.f. is induced in one circuit when the current in the other circuit changes from 0 to 20 A in 0.02 s?
  169. Two circuits have coefficient of mutual induction of 0.09 henry. Average e.m.f. induced in the secondary by a change of current from 0 to 20 amperes in 0.006 second in the primary will be
  170. The adjoining figure shows two bulbs B 1 and B 2 resistor R and an inductor L. When the switch S is turned off,
  171. Energy stored in a coil of self-inductance 40 mH carrying a steady current of 2 A is
  172. A conducting ring of radius 1 m is placed in a uniform magnetic field B of 0.01 T oscillating with frequency 100 Hz with its plane at right angle to B. What will be the induced electric field?
  173. In the given circuit, let i 1 be the current drawn from battery at time t = 0 and i 2 be steady current at t = ∞ , then the ratio i 1 i 2 is
  174. Statement 1: Time dependent magnetic field generates electric field. Statement 2: Direction of electric field generated from time variable magnetic field does not obey Lenz’s law.
  175. Statement 1: The growth of current in R-L circuit is uniform. Statement 2: Inductor opposes the growth of current.
  176. Statement 1: The quantity L/R possesses dimensions of time. Statement 2: To reduce the rate of increases of current through a solenoid, one should increase the time constant (L/R).
  177. In a circular conducting coil, when current increases from 2 A to 18 A in 0.05 s, the induced e.m.f. is 20 V. The self-inductance of the coil is
  178. A solenoid has an inductance of 60 henrys and a resistance of 30 ohms. If it is connected to a 100 volt battery, how long will it take for the current to reach e − 1 e ≈ 63.2 % of its final value
  179. A coil of inductance 300 mH and resistance 2 Ω is connected to a source of voltage 2V. The current reaches half of its steady state value in
  180. In the circuit shown, switch S is closed at time t = 0. The charge which passes through the battery in one time constant is
  181. In the figure, magnetic energy stored in the coil is
  182. The self-induced e.m.f. in a 0.1 H coil when the current in it is changing at the rate of 200 A/s is
  183. The potential difference across a 4H inductor vary with time as shown. The current is zero at time t=0. The current (in A) at time t=2 sec is
  184. A copper wire of length 2 m placed perpendicular to the plane of magnetic field B = ( 2 i ^ + 4 j ^ ) T.If it moves with velocity ( 4 i ^ + 6 j ^ + 8 k ^ ) m/sec. The magnitude of dynamic emf (in volt) across its ends is .
  185. A light straight slider 1 m long can slide over two straight long parallel rails, vertically kept. when a uniform magnetic field of 0.6 T is applied perpendicular to the plane of rails, the slider is found moving with a constant velocity. At this instant power dissipated in rails and slider due to their resistance is 1.96 W. If slider has a mass of 0.2kg, then the terminal velocity of the slider is .
  186. Wire PQ with negligible resistance slides on the three rails with 5 cm/sec. If the current in 10 Ω resistance when switch S is connected to position 1 is i 1 and when the switch is at position 2 the current becomes i 2 .Then the ratio i 1 /i 2 is .
  187. A structure formed from two straight conducting rods forming a right angle, is placed in a uniform magnetic field with B = 0.40 T is directed out of the page. A straight conducting bar in contact with the structure, starts at the vertex at time t = 0 and moves with a constant velocity of 5.0 m/s along them. The emf (in V) around the triangle at that time t=4.0 s is .
  188. Two different loops are concentric and lie in the same plane. The current in the outer loop is clockwise and increasing with time. The induced current in the inner loop, then, is
  189. A wire is bent to form the double loop shown in figure. There is a uniform magnetic field directed into the plane of the loop. If the magnitude of this field is decreasing, current will flow from
  190. A metallic rod AB of length 1.5 m is made to move in a uniform magnetic field of 2 tesla with a velocity of 2 m/s as shown in figure. Then electro static field that appears in the rod is
  191. The current flowing in two coaxial coils are in the same direction. On increasing the distance between the two, the electric current in both the cables will
  192. A current carrying solenoid is approaching a conducting loop as shown in the figure. The direction of induced current as observed by an observer on the other side of the loop will be
  193. The north and south poles of two identical magnets approach a coil containing a condenser, with equal speeds from opposite sides. Then
  194. A capacitor of capacitance C’ has initial charge Q 0 and connected to inductor ‘L’ as shown, at t = 0 switch S is pressed. The current through the inductor when energy in the capacitor is three times of the energy of the inductor is
  195. A square coil 10 -2 m 2 area is placed perpendicular to a uniform magnetic field of intensity 10 3 Wb/m 2 . The magnetic flux through the coil is
  196. As shown in the figure, a magnet is moved with a fast speed towards a coil at rest. Due to this induced electromotive force, induced current and induced charge in the coil is E,I and Q respectively. If the speed of the magnet is doubled, the incorrect statement is
  197. When a magnet is pushed in and out of a circular coil C connected to a very sensitive galvanometer G as shown in the adjoining diagram with a frequency v, then
  198. A coil of area 100 cm 2 has 500 turns. Magnetic field of 0.1 weber/metre 2 is perpendicular to the coil. The field is reduced to zero in 0.1 second. The induced e.m.f. in the coil is
  199. A coil having an area 2m 2 is placed in a magnetic field which changes from 1Wb/m 2 to 4Wb/m 2 in a interval of 2 second. The e.m.f. induced in the coil will be
  200. The magnetic field in a coil of 100 turns and 40 square cm area is increased from 1 Tesla to 6 Tesla in 2 second. The magnetic field is perpendicular to the coil. The e.m.f. generated in it is
  201. The north pole of a long horizontal bar magnet is being brought closer to a vertical conducting plane along the perpendicular direction. The direction of the induced current in the conducting plane will be
  202. The dimensions of magnetic flux are
  203. A coil of 100 turns and area 5 square centimetre is placed in a magnetic field B = 0.2 T. The normal to the plane of the coil makes an angle of 60° with the direction of the magnetic field. The magnetic flux linked with the coil is
  204. A rectangular coil of 20 turns and area of cross- section 25 sq cm has a resistance of 100 ohm. If a magnetic field which is perpendicular to the plane of the coil changes at the rate of 1000 Tesla per second, the current in the coil is
  205. The total charge induced in a conducting loop when it is moved in magnetic field depends on
  206. A coil has an area of 0.05 m 2 and it has 800 turns. It is placed perpendicularly in a magnetic field of strength 4 × 10 − 5 Wb / m 2 it is rotated through 90 ∘ in 0.1 sec. The average e.m.f. induced in the coil is
  207. Magnetic flux ϕ (in weber) linked with a closed circuit of resistance 10 ohm varies with time t (in seconds) as ϕ = 5 t 2 − 4 t + 1 The induced electromotive force in the circuit at t = 0.2 sec. is
  208. Lenz’s law is expressed by the following formula (here e = induced e.m.f., ϕ = magnetic flux in one turn and N = number of turns)
  209. The magnetic flux linked with a vector area A in a uniform magnetic field B is
  210. An electric potential difference will be induced between the ends of the conductor shown in the diagram, when the conductor moves in the direction
  211. A 10 metre wire kept in east-west falling with velocity 5 m/sec perpendicular to the field 0.3 × 10 − 4 Wb / m 2 . The induced e.m.f. across the terminal will be
  212. A copper disc of radius 0.1 m is rotated about its centre with 10 revolutions per second in a uniform magnetic field of 0.1 Tesla with its plane perpendicular to the field. The e.m.f. induced across the radius of disc is
  213. A conducting square loop of side L and resistance R moves in its plane with a uniform velocity v perpendicular to one of its sides. A magnetic induction B constant in time and space, pointing perpendicular and into the plane of the loop exists everywhere. The current induced in the loop is
  214. A metal rod moves at a constant velocity in a direction perpendicular to its length. A constant uniform magnetic field exists in space in a direction perpendicular to the rod as well as its velocity. Select the correct statement(s) from the following
  215. One conducting U tube can slide inside another as shown in figure, maintaining electrical contacts between the tubes. The magnetic field B is perpendicular to the plane of the figure. If each tube moves towards the other at a constant sped v then the emf induced in the circuit in terms of B, l and v where l is the width of each tube, will be
  216. The back e.m.f. induced in a coil, when current changes from 1 ampere to zero in one milli second, is 4 volts, the self inductance of the coil is
  217. The current passing through a choke coil of 5 henry is decreasing at the rate of 2 ampere/sec. The e.m.f. developing across the coil is
  218. Two coils of self inductance L 1 and L 2 are placed closer to each other so that total flux in one coil is completely linked with other. If M is mutual inductance between them, then
  219. The momentum in mechanics is expressed as m × v . The analogous expression in electricity is
  220. A coil of wire of a certain radius has 600 turns and a self inductance of 108 mH. The self inductance of a 2 nd similar coil of 500 turns will be
  221. The self inductance of a solenoid of length L, area of cross-section A and having N turns is
  222. The self inductance of a straight conductor is
  223. The current in a coil changes from 4 ampere to zero in 0.1 s. If the average e.m.f. induced is 100 volt, what is the self inductance of the coil?
  224. If in a coil rate of change of area is 5 m 2 /milli second and current become 1 amp from 2 amp in 2 × 10 − 3   sec . If magnitude of field is 1 tesla then self inductance of the coil is
  225. The equivalent inductance of two inductances is 2.4 henry when connected in parallel and 10 henry when connected in series. The difference between the two inductances is
  226. An e.m.f. of 12 volt is produced in a coil when the current in it changes at the rate of 45 amp/minute. The inductance of the coil is
  227. If a change in current of 0.01 A in one coil produces a change in magnetic flux of 1.2 × 10 − 2 W b in the other coil, then the mutual inductance of the two coils in henries is
  228. A solenoid of length l metre has self-inductance L henry. If number of turns are doubled, its self inductance
  229. In a circular conducting coil, when current increases from 2 A to 18 A in 0.05 sec., the induced e.m.f. is 20 V. The self inductance of the coil is
  230. Which of the following is not the unit of self inductance
  231. A coil of 100 turns carries a current of 5 mA and creates a magnetic flux of 10 –5 weber. The inductance is
  232. In circular coil, when no. of turns is doubled and resistance becomes 1 4 t h of initial, then inductance becomes
  233. The self-induced e.m.f. in a 0.1 H coil when the current in it is changing at the rate of 200 ampere/second is
  234. A coil resistance 20 Ω and inductance 5H is connected with a 100V battery. Energy stored in the coil will be
  235. Two circular coils have their centres at the same point. The mutual inductance between them will be maximum when their axes
  236. The current in a coil decreases from 1 A to 0.2 A in 10sec. Calculate the coefficient of self inductance if induced emf is 0.4 volt.
  237. If the current 30 A flowing in the primary coil is made zero in 0.1 sec. The emf induced in the secondary coil is 1.5 volt. The mutual inductance between the coil is
  238. A coil having an inductance of 0.5 H carries a current which is uniformly varying from zero to 10 ampere in 2 second. The e.m.f. (in volts) generated in the coil is
  239. The core of a transformer is laminated to reduce energy losses due to
  240. The device that does not work on the principle of mutual induction is
  241. Choke coil works on the principle of
  242. The output of a dynamo using a splitting commutator is
  243. Dynamo core is laminated because
  244. The armature of dc motor has 20   Ω resistance. It draws current of 1.5 ampere when run by 220 volts dc supply. The value of back e.m.f. induced in it will be
  245. In an induction coil, the secondary e.m.f. is
  246. The number of turns in the coil of an ac¬ generator is 5000 and the area of the coil is 0 .25   m 2 . The coil is rotated at the rate of 100 cycles/sec in a magnetic field of 0.2 W / m 2 . The peak value of the emf generated is nearly
  247. Fan is based on
  248. A motor having an armature of resistance 2 Ω is designed to operate at 220 V mains. At full speed, it develops a back e.m.f. of 210V. When the motor is running at full speed, the current in the armature is
  249. The core of a transformer is laminated so that
  250. If a coil made of conducting wires is rotated between poles pieces of the permanent magnet. The motion will generate a current and this device is called
  251. A copper rod of length l is rotated about one end perpendicular to the magnetic field B with constant angular velocity ω . The induced e.m.f. between the two ends is
  252. Two conducting circular loops of radii R 1 and R 2 are placed in the same plane with their centers coinciding. If R 1 > > R 2 , the mutual inductance M between them will be directly proportional to
  253. A short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be
  254. As shown in the figure a metal rod makes contact and complete the circuit. The circuit is perpendicular to the magnetic field with B = 0 .15   tesla . If the resistance is 3   Ω , force needed to move the rod as indicated with a constant speed of 2 m / sec is
  255. A conducting wire frame is placed in a magnetic field which is directed into the paper. The magnetic field is increasing at a constant rate. The directions of induced current in wires AB and CD are
  256. A square metallic wire loop of side 0.1 m and resistance of 1 Ω is moved with a constant velocity in a magnetic field of 2 wb/m 2 as shown in figure. The magnetic field is perpendicular to the plane of the loop, loop is connected to a network of resistances. What should be the velocity of loop so as to have a steady current of 1mA in loop
  257. The resistance in the following circuit is increased at a particular instant. At this instant the value of resistance is 10 Ω . The current in the circuit will be now
  258. A conducting ring is placed around the core of an electromagnet as shown in fig. When key K is pressed, the ring
  259. A highly conducting ring of radius R is perpendicular to and concentric with the axis of a long solenoid as shown in fig. The ring has a narrow gap of width d in its circumference. The solenoid has cross sectional area A and a uniform internal field of magnitude B 0 . Now beginning at t = 0, the solenoid current is steadily increased to so that the field magnitude at any time t is given by B(t) = B 0 + α t where α >0 . Assuming that no charge can flow across the gap, the end of ring which has excess of positive charge and the magnitude of induced e.m.f. in the ring are respectively
  260. A rectangular loop with a sliding connector of length l = 1.0 m is situated in a uniform magnetic field B = 2T perpendicular to the plane of loop. Resistance of connector is r = 2 Ω . Two resistance of 6 Ω and 3 Ω are connected as shown in figure. The external force required to keep the connector moving with a constant velocity v = 2m/s is
  261. A conducting ring of radius 1 meter is placed in an uniform magnetic field B of 0.01Telsa oscillating with frequency 100Hz with its plane at right angles to B. What will be the induced electric field
  262. A conductor rod AB moves parallel to X-axis in a uniform magnetic field, pointing in the positive X-direction. The end A of the rod gets
  263. A conducting square loop of side L and resistance R moves in a plane with a uniform velocity v perpendicular to one of its side. A magnetic induction B constant in time and space, pointing perpendicular and into the plane of the loop exists everywhere. The current induced in the loop is
  264. Fig.(6) represents an area A = 0.5m 2 situated in a uniform magnetic field B = 2.0weber/m 2 and making an angle of 60 o with respect to magnetic field. The value of the magnetic flux through the area would be equal to
  265. A rectangular loop of sides 8 cm and 2 cm having resistance of 1.6 Ω is placed in a magnetic field of 0.3 T directed normal to the loop. The magnetic field is gradually reduced at the rate of 0.02 T/s. How much power is dissipated by the loop as heat ?
  266. A solenoid has 2000 turns wound over a length of 0.30 m. The area of its cross-section is 1 .2 x 10 -3 m 2 . Around its central section of a coil of 300 turns is wound. If an initial current of 2 A in the solenoid is reversed in 0.25 sec., the e.m.f. induced in the coil is equal to
  267. The spokes of a wheel are metallic and their length is 0.5 m. On rotating the wheel at right angles to a uniform magnetic field of 5 x 10 -4 tesla, a potential difference of 3.14 mV is produced between the rim and the axis. The rotational speed of the wheel is
  268. A 50 Hz a.c. current of crest value 1 A flows through the primary of a transformer. If the mutual inductance between the primary and secondary be 1.5 H, the crest voltage induced in the secondary is
  269. A small loop of area of cross-section 10 -4 m 2 is lying concentrically and coplanar inside a bigger loop of radius 0.628 m. A current of 10 A is passed in the bigger loop. The smaller loop is rotated about its diameter with an angular velocity ω . The magnetic flux linked with the small loop will be
  270. If a current of 3 amperes flowing in the primary coil is reduced to zero in 0.001 second, then the induced e.m.f. in the secondary coil is 15000 volts. The mutual inductance between the two coils is
  271. A long solenoid having 200 turns per cm carries a current of 1.5 amp. At the can be of it is placed a coil of 100 turns of cross-sectional area 3.14 x 10 -4 m 2 having its axis parallel to the field produced by the solenoid. When the direction of current in the solenoid is reversed within 0.05 sec, the induced e.m.f. in the coil is
  272. A thin semicircular conducting ring of radius R is falling with its plane vertical in a horizontal magnetic induction B fig. (12). At the position MNQ the speed of ring is V and potential difference developed across the ring is
  273. Two different coils have self-inductances L 1 = 8 mH, L 2 =2 mH. The current in one coil is increased at aconstant rate. The current in the second coil is also increased at the same rate. At a certain instant of time, the power given to the two coils is the same. At that time the current, the induced voltage and the energy stored in the first coil are i 1 V 1 and W 1 respectively. Corresponding value for the second coil at the same instant are i 2 , V 2 and W 2 respectively. Then
  274. A coil of copper having 1O0O turns is placed in a magnetic field (B = 4x 10 -3 T) perpendicular to its axis. The cross-sectional area of the coil is 0.05 m 2 . If it turns through 180 o in 0.01 sec, then the e.m.f. induced in the coil is
  275. Two pure inductor coils of self inductance L each are connected in series, the net inductance is
  276. A coil of wire of radius r has 600 turns and a self inductance of 108 mH. The self inductance of a similar coil of 500 turns will be
  277. A rectangular loop with a sliding connector of Iength 10 cm is situated in a uniform magnetic field perpendicular to plane of loop. The magnetic induction is 0.1 T and resistance of connector (R) is 1 ohm. The sides AB and CD have resistances 2 ohm and 3 ohm respectively. Find the current in the connector during its motion with constant velocity one metre/sec.
  278. Two identical circular loops of metal wire are lying on a table without touching each other. Loop-A carries a current which increases with time. In response, the loop-B
  279. A wire shaped as a semicircle of radius o rotates about an axis OO’ with an angular velocity ω in a uniform magnetic field of induction B [Fig. (5)]. The rotation axis is perpendicular to the field direction. The total resistance of the circuit is equal to fl. Neglect the magnetic field of induced current. The mean amount of thermal power being generated into the loop during a rotation period will be
  280. A metallic square loop ABCD is moving in its own plane with velocity v in a uniform magnetic field perpendicular to its plane as shown in fig. An electric field is induced
  281. A short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of tums were to be quadrupled and the wire radius halved, the electric power dissipated would be
  282. In figure a long straight wire carries a steady current I. A conducting rod is in contact with a pair of rails, and rotates about the straight wire. The induced current in the resistor R is
  283. Figure shows a ring of radius ‘a’ at t = 0, present in a uniform magnetic field B. The magnetic field is present everywhere parallel to the axis yy ‘ . If ring starts rotating with an angular speed ω about axis yy ‘ , the induced emf in ring is
  284. A frame CDEF is placed in a region where a magnetic field B is present. A rod of length one metre moves with constant velocity 20 m/s and strength of magnetic field is one tesla. The power spent in the process is (take R = 0 . 2 Ω and all other wires and rod have zero resistance)
  285. The magnetic potential energy stored in a certain inductor is 25 m J , when the current in the inductor is 60 m A . This inductor is of inductance
  286. 24. A wire of length 2 m is moving at a speed of 5 ms – 1 perpendicular to its length and a homogeneous magnetic field of 0.5 T. The ends of the wire are joined to a circuit of resistance 10 Ω . The rate at which work is being done to keep the wire moving at constant speed is
  287. An inductor of 5 henry and a resistance of 10 ohms are connected in series with a battery of 15 volts. The initial rate of change of current is
  288. Two circular loops of equal radii are placed coaxially at some separation. The first is cut and a battery is inserted to drive a current in it. The current changes slightly because of the variation in resistance with temperature (produced due to current in the circuit). During this period, the two loops.
  289. A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from
  290. A metallic rod of mass per unit length 0.5 kg m – 1 is lying horizontally on a smooth inclined plane which makes an angle of 30 0 with the horizontal. The rod is not allowed to slide down by flowing a current through it when a magnetic field of induction 0.25 T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is
  291. A thin semicircular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure. The potential difference developed across the ring when its speed ν , is
  292. A uniform magnetic field exists in the region given by B = 3 i ^ + 4 j ^ + 5 k ^ . A rod of length 5 m placed along Y-axis is moved along X-axis with constant speed 1   ms − 1 . Then induced e.m.f in the rod is
  293. A physicist works in a laboratory where the magnetic field is 4 T. She wears a necklace enclosing area 0.01 m 2 in such a way that the plane of the necklace is normal to the field and is having a resistance R = 0.01 Ω . Because of power failure, the field decays to 1 T in time 10 – 3 seconds. Then what is the total heat produced in her necklace? (T = Tesla)
  294. A 800 turn coil of effective area 0 . 05 m 2 is kept perpendicular to a magnetic field 5 × 10 – 5 T . When the plane of the coil is rotated by 90 ° around any of its coplanar axis in 0.1 s, the emf induced in the coil will be
  295. A semicircular wire of radius R is rotated with constant angular velocity ω about an axis passing through one end and perpendicular to the plane of the wire. There is a uniform magnetic field of strength B. The induced e.m.f. between the ends is:
  296. At t =0, an inductor of zero resistance is joined to a cell of emf through a resistance. The current increases with a time constant τ . After what time will the potential difference across the coil be equal to that across the resistance?
  297. An electron moves on a straight line path X Y as shown. The a b c d is a coil adjacent to the path of electron. What will be the direction of current, if any, induced in the coil?
  298. A wire loop is rotated in a magnetic field. The frequency of change of direction of the induced e.m.f. is
  299. An equilateral triangular loop having a resistance R and length of each side l is placed in a magnetic field which is varying at d B d t = 4 T / s . The induced current in the loop will be
  300. A uniform magnetic field is restricted within a region of radius “r”. The magnetic field changes with time at a rate d B d t . Loop 1 of radius R > r encloses the region r and loop 2 of radius R is outside the region of magnetic field as shown in the figure. Then the e.m.f. generated is
  301. A conducting square frame of side ‘a’ and a long straight wire carrying current I are located in the same plane as shown in the figure. The frame moves to the right with a constant velocity ‘ V ‘. The emf induced in the frame will be proportional to
  302. A current of 2.5 A flows through a coil of inductance 5H The magnetic flux linked with the coil is
  303. A rectangular loop with a sliding connector of length l = 1.0 m is situated in a uniform magnetic field B = 2T perpendicular to the plane of loop. Resistance of connector is r = 2 Ω . Two resistance of 6 Ω and 3 Ω are connected as shown in figure. The external force required to keep the connector moving with a constant velocity v = 2m/s is
  304. A square loop of side a is placed such that its plane is the same as that of a very long straight wire carrying a current I. The centre O of the loop is at a distance x from the wire. The loop is given a velocity v as shown. If x >> a, the magnitude of the emf induced in the loop is proportional to
  305. In a coil of resistance of 10 Ω , the induced current developed by changing magnetic flux through it, is shown in figure as a function of time. The magnitude of change in flux through the coil in Weber is
  306. A long solenoid of diameter 0.1 m has 2 × 10 4 turns per meter. At the centre of the solenoid, a coil of 100 turns and radius 0.01 m is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to 0 A from 4 A in 0.05 s. If the resistance of the coil is 10π 2 Ω , the total charge flowing through the coil during this time is
  307. Figure shows a circuit that contains three identical resistors with resistance R = 9.0 Ω each, two identical inductors with inductance L = 2.0 mH each, and an ideal battery with emf ε = 18 V. The current i through the battery just after the switch closed is
  308. A wheel with 20 metallic spokes each 1 m long is rotated with a speed of 120 rpm in a plane perpendicular to a magnetic field of 0.4 G. The induced emf between the axle and rim of the wheel will be ( 1 G = 10 – 4 T )
  309. The magnetic flux linked with a coil (in Wb) is given by the equation ϕ = 5 t 2 + 3 t + 16 . The magnitude of induced emf in the coil at the fourth second will be
  310. In the circuit, 1&2 are joined for long time. After disconnecting 1&2, 2&3 are connected. The charge on the capacitor when the current in the inductor (ideal) decreases by 3A is [nearly]
  311. The mutual inductance between two planar concentric rings of radii r 1 a n d r 2 (with r 1 > r 2 ) placed in air is given by
  312. A rod is falling vertically along a smooth rail in a uniform magnetic field as shown in the figure. If the mass of the rod is ‘m’ and length ‘l’ and resistance ‘R’, then the height through which it has to fall so that it attains terminal velocity
  313. As shown in the figure a metal rod makes contact and completes the circuit. The circuit is perpendicular to the magnetic field with B = 0.5   t e s l a . If the resistance is 3   Ω , work done by magnetic force to move the rod as indicated with a constant speed of 2   m / s e c for 3 sec is.
  314. A uniform rod of length L is moved with constant velocity V in a uniform magnetic field over the rails as shown in fig. Which of the following directions represents the direction of magnetic force on an electron moving along the rod.( Uniform magnetic field is into the plane of the paper).
  315. A circuit containing capacitors C 1 and C 2 as shown in the figure are in steady state with key K 1 closed and K 2 is opened. At the instant t = 0, if K 1 is opened and K 2 is closed then the maximum current in the circuit will be :
  316. A metallic ring of radius 1 m is placed in a uniform magnetic field of induction 1 μ T with its plane perpendicular to the direction of magnetic field. Now the radius of the ring is halved in a time interval of 0.1 second. Then average emf induced in the ring is
  317. A thin rod AB of length 2m is moving with velocity v = 3    m / s in a uniform magnetic field of induction B = 1.5 Tesla, Direction of velocity vector makes an angle of θ = 30 0 with the length of the rod. Then potential difference between the ends is given by
  318. A current I 0 is flowing through on L – R circuit of time constant t 0 . The source of current is switched off at time t = 0. Let r be the value of − dI dt at t = 0. Assuming this rate to be constant, the current will reduce to zero in a time interval of
  319. The magnetic field of an electromagnetic wave obeys the relation in a certain region is B = 10 − 12 sin ( 1 × 10 6 t ) in tesla, where ‘ t ‘ is the time. Then, the induced emf , in a 100 turns in coil of area 10cm 2 oriented perpendicular to the field is
  320. The magnetic field of an electromagnetic wave , obeys the relation in a certain region , is B = 10 − 12 sin ( 5 × 10 6 t ) T , where t is the time . Then the induced emf , in a 300 turns coil of area 20cm 2 oriented perpendicular to the field is
  321. A toroidal solenoid with an air core has an average radius of 15 cm, area of cross section 12 cm 2 and 1200 turns. Ignoring the field variation across the cross-section of the toroid, the self inductance of the toroid is
  322. A rectangular loop of sides 10 cm and 5 cm with a cut is stationary between the pole pieces of an electromagnet. The magnetic field of the magnet is normal to the loop. The current feeding the electromagnet is reduced so that the field decreases from its initial value of 0.3 T at the rate of 0.02 T s – 1 . If the cut is joined and the loop has a resistance of 2.0 W, the power dissipated by the loop as heat is
  323. A metal rod of resistance 20 Ω is fixed along a diameter of a conducting ring of radius 0.1m and lies on x-y plane. There is a magnetic field B = ( 50 T ) k ^ . The ring rotates with an angular velocity w = 20 rad s-1 about its axis. An external resistance of 10 Ω is connected across the center of the ring and rim. The current through external resistance is
  324. A coil of inductance 0.20 H is connected in series with a switch and a cell of emf 1.6 V. The total resistance of the circuit is 4.0 W. What is the initial rate of growth of the current when the switch is closed?
  325. A coil of Cu wire (radius r, self-inductance L) is bent in two concentric circular turns each having radius r 2 . The self-inductance now
  326. The loop PQ, as shwon in figure moves with a velocity . Both loop and velocity are in the plane of paper and a magnetic field exists in the region perpendicular to plane and directed inward. Find the emf induced between P and Q.
  327. Which of the following statements is /are correct
  328. A square loop of side a is placed such that its plane is the same as that of a very long straight wire carrying a current I. The centre O of the loop is at a distance x from the wire. The loop is given a velocity v as shown. If x >> a, the magnitude of the emf induced in the loop is proportional to
  329. A 0.1 m long conductor carrying a current of 50 A is perpendicular to a magnetic field of 1.21 mT. The mecha­nical power to move the conductor with a speed of 1 m s – 1 is
  330. A long solenoid of radius R carries a time (t) – dependent current I t = I 0 t 1 − t . A ring of radius 2R is placed coaxially near its middle. During the time interval 0 ≤ t ≤ 1 , the inducted current I R and the induced EMF ( V R ) in the ring changes as:
  331. Consider a circular coil of wire carrying constant current I, forming a magnetic dipole. The magnetic flux through an infinite plane that contains the circular coil and excluding the circular coil area is given by ϕ i . The magnetic flux through the area of the circular coil is given by ϕ 0 . Which of the following option is correct?
  332. A loop ABCDEFA of straight edges has six corner points A(0,0,0), B(5,0,0), C(5,5,0), D(0,5,0), E(0,5,5) and F(0,0,5). The magnetic field in this region is B = ( 3 i ^ + 4 k ^ ) T . The quantity of flux through the loop ABCDEFA (in Wb) is .
  333. A planar loop of wire rotates in a uniform magnetic field. Initially, at t=0, the plane of the loop is perpendicular to the magnetic field. If it rotates with a period of 10s about an axis in its plane then the magnitude of induced emf will be maximum and minimum, respectively at:
  334. In the network shown, time constant of the circuit is ς when switches S 1 and S 2 are open. When S 1 and S 2 are closed, time constant of the circuit will be
  335. Magnetic flux linked with a stationary loop of resistance 10 Ω varies with time according to the ϕ − t graph shown in figure. Then total heat generated in the loop is
  336. A circular metallic has a resistance 10 Ω . Area enclosed by the ring is 0 .5 m 2 . The ring is placed in a uniform magnetic field with its plane perpendicular to the field. The magnetic field is decreasing at the rate of 5 Tesla/sec. then total charge flown through a cross section of the wire of the ring in 10 second is
  337. A thin copper rod PQ of length 1 m is made to move with velocity V = 2 m/s in a uniform magnetic field of induction B = 1.5 Tesla as shown in the figure. Then induced potential difference between points P and R is
  338. In the network shown, switch s is closed at t=0. Then which of the following graphs correctly shown the variation of induced emf between points ‘a’ and ‘b’?
  339. In a fluorescent lamp choke (a small transformer ) 100 V of reverse voltage is produced when the choke current changes uniformly from 0.25 A to 0 in a duration of 0.025 ms. The self –inductance of the choke (in mH) is estimated to be
  340. An aeroplane is moving towards north horizontally with a speed of 200 m s – 1 at a place where the vertical component of earth’s magnetic field is 0.5 x 10 – 4 tesla. Then the induced e.m.f. set up between the tips of the wings of the plane if they are 10 m apart is
  341. A current of 5A is flowing through a 0.5 H inductor. If the current starts increasing at a rate of 2 A/S, power consumption by the inductor will be
  342. A closed loop made up of insulating material, having cross-sectional area 10   cm 2 is placed in a varying magnetic field which is increasing at the rate of 10T/s. The plane of the loop is perpendicular to magnetic field. Calculate the induced emf and induced current.
  343. A compass needle is placed in the gap of a parallel plate capacitor. The capacitor is connected to a battery through a resistance. The compass needle
  344. The inductance of a coil in which a current of 0.1 A increasing at the rate of 0.5 A/s represents a power flow of 0.5 watt is
  345. An elliptical loop having resistance R, of semi major axis a, and semi minor axis b is placed in a magnetic field as shown in the figure. If the loop is rotated about the x-axis with angular frequency ω , the average power loss in the loop due to Joule heating is:
  346. A uniform magnetic field B exists in a direction perpendicular to the plane of a square loop made of a metal wire. The wire has a diameter of 4mm and a total length of 30 cm. The magnetic field changes with time at a steady rate d B d t = 0 . 032 T s – 1 . The induced current in the loop is close to (Resistivity of the metal wire is 1.23 × 10 − 8 Ω m )
  347. A small bar magnet is moved through a coil at constant speed from one end to the other. Which of the following series of observations will be seen on the galvanometer G attached across the coil ? Three positions shown describe : (a) the magnet’s entry (b) magnet is completely inside and (c) magnet’s exit.
  348. Two concentric circular coils, C 1 and C 2 are placed in the X Y plane. C 1 has 500 turns, and a radius of 1 cm . C 2 has 200 turns and radius of 20 cm . C 2 carries a time dependent current I t = ( 5 t 2 − 2 t + 3 ) A where t is in s . The emf induced in C 1 (in mV),at the instant t = 1 s   i s   4 x . The value of x is
  349. Magnetic flux linked with a coil of radius 10   Ω is given by ϕ = ( 20 − 3 t 2 ) weber where t is time in second. Then total charge flown through the coil in the interval from t = 0 to t = 2S is
  350. Relative position of two coils 1 and 2 is fixed. Coil 1 is carrying no current and when the current in coil 2 is increasing at a constant rate of 10 A/S, the emf induced in coil 1 is 20 mV. Find the magnetic flux linked with coil 2, which is not carrying any current, when coil 1 is carrying a current of 10 A.
  351. A metallic ring, having area 1 m 2 and resistance 10   Ω is held in a uniform magnetic field of induction 2   μ T with its plane perpendicular to the field. If the field is switched off in a time interval of 0.1 second, then the average current induced is
  352. The iron core of a solenoid has a length of 40 cm and a cross-section of 4.0 cm x cm, and is wound with 10 turns of wire per cm of length. Compute the inductance of the solenoid, assuming the relative permeability of the iron to be constant at 500.
  353. Current flowing through a coil increases from zero to 5A in 0.02 second. If emf induced in the coil is 30 volt, the self inductance of the coil is
  354. In an induction coil the coefficient of mutual inductance is 4H. If current of 5A in the primary coil is cut off in 1 1500 seconds, the emf at the terminals of secondary coil is
  355. Figure shows a square loop of side 1m and resistance 1   Ω the magnetic field on left side of line PQ has a magnitude B = 1T. The work done in pulling the loop out of the field uniformly in 1s is
  356. A conducting rod of length l is hinged at point O. It is free to rotate in a vertical plane. There exists a uniform magnetic field B in horizontal direction. The rod is released from the horizontal position as shown. The potential difference between the ends of the rod when it has turned by θ (as shown in figure) is proportional to
  357. The variation of induced emf (E) with time (t) in a coil if a short bar magnet is moved along its axis with a constant velocity is best represented as
  358. A conducting wire frame is placed in a magnetic field which is directed into the paper. The magnetic field is increasing at a constant rate. The directions of induced current in wires AB and CD are
  359. The figure shows four wire loops, with edge lengths of either L or 2L. All four loops will move through a region of uniform magnetic field B (directed out of the page) at the same constant velocity. Rank the four loops according to the maximum magnitude of the e.m.f. induced as they move through the field, greatest first
  360. A square loop of side 5 cm enters a magnetic field with 1 cms -1 . The front edge enters the magnetic field at t = 0 then which graph best depicts emf
  361. A thin semicircular conducting ring of radius R is falling with its plane vertical in a horizontal magnetic induction B. At the position MNQ, the speed of the ring is v and the potential difference developed across the ring is
  362. A small square loop of wire of side / is placed inside a large square loop of wire of side L (L > l ). The loop are coplanar and their center coincide. The mutual inductance of the system is proportional to
  363. A uniform but time-varying magnetic field B(t) exists in a circular region of radius a and is directed into the plane of the paper, as shown. The magnitude of the induced electric field at point P at a distance r from the center of the circular region
  364. The resistance in the following circuit is increased at a particular instant. At this instant the value of resistance is 10 Ω . The current in the circuit will be now
  365. The network shown in the figure is a part of a complete circuit. If at a certain instant the current i is 5A and is decreasing at the rate of 10 3 A/s then V A – V B is
  366. The current through a 4.6 H inductor is shown in the following graph. The induced emf during the time interval t= 5 milli-sec to 6 milli-sec will be
  367. An aluminum ring B faces an electromagnet A. The current i through A can be altered
  368. For the solenoids shown in the diagram (which are assumed to be close to each other), the resistance of the left-hand circuit is slowly increased. In which direction does the current flow through galvanometer in the right-hand circuit?
  369. A thin circular ring of area A is perpendicular to uniform magnetic field of induction B. A small cut is made in the ring and a galvanometer is connected across the ends such that the total resistance of circuit is R. When the ring is suddenly squeezed to zero area, the charge flowing through the galvanometer is
  370. A long conducting wire AH is moved over a conducting triangular wire CDE with a constant velocity v in a uniform magnetic field B directed into the plane of the paper. Resistance per unit length of each wire is ρ . Then
  371. A conducting wire frame is placed in a magnetic field which is directed into the plane of the paper (figure). The magnetic field is increasing at a constant rate. The directions of induced currents in wires AB and CD are
  372. A horizontal ring of radius r = 1/2 m is kept in a vertical constant magnetic field 1 T. The ring is collapsed from maximum area to zero area in 1 s. Then the emf induced in the ring is
  373. An equilateral triangular loop ADC having some resistance is pulled with a constant velocity v out of a uniform magnetic field directed into the paper (figure). At time t = 0, side DC of the loop is at edge of the magnetic field. The induced current (i) versus time (t) graph will be as
  374. The four wire loops shown in figure have vertical edge lengths of either L,2L, or 3L. They will move with the same speed into a region of uniform magnetic field B directed out of the page. Rank them according to the maximum magnitude of the induced emf greatest to least.
  375. A wire is sliding as shown in figure. The angle between the acceleration and the velocity of the wire is
  376. A conductor of length I and mass m can slide without any friction along the two vertical conductors connected at the top through a capacitor (figure). A uniform magnetic field B is setup ⊥ to the plane of paper. The acceleration of the conductor
  377. A rectangular loop with a sliding conductor of length l is located in a uniform magnetic field perpendicular to the plane of the loop (figure). The magnetic induction is B. The conductor has a resistance R. The sides AB and CD have resistances R 1 and R 2 , respectively. Find the current through the conductor during its motion to the right with a constant velocity v.
  378. A conducting wire of mass m slides down two smooth conducting bars, set at an angle θ to the horizontal as shown in figure. The separation between the bars is l . The system is located in the magnetic field B, perpendicular to the plane of the sliding wire and bars. The constant velocity of the wire is
  379. A conducting ring of radius r is rolling without slipping with a constant angular velocity ω (figure). If the magnetic field strength is B and is directed into the page then the emf induced across PQ is
  380. A semicircular wire of radius R is rotated with constant angular velocity about an axis passing through one end and perpendicular to the plane of the wire. There is a uniform magnetic field of strength B. The induced emf between the ends is
  381. Two identical cycle wheels (geometrically) have different number of spokes connected from center to rim. One is having 20 spokes and the other having only 10 (the rim and the spokes are resistanceless). One resistance of value R is connected between center and rim. The current in R will be
  382. A square non-conducting loop, 20 cm, on a side is placed in a magnetic field. The center of side AB coincides with the center of magnetic field. The magnetic field is increasing at the rate of 2 T/s. The potential difference between C and D is
  383. A line charge I per unit length is pasted uniformly onto the rim of a wheel of mass m and radius R. The wheel has light non-conducting spokes and is free to rotate about a vertical axis as shown in figure. A uniform magnetic field B exists as shown in figure. What is the angular velocity of the wheel when the field is suddenly switched off?
  384. A conducting ring of radius r and resistance R rolls on a horizontal surface with constant velocity v. The magnetic field B is uniform and is normal to the plane of the loop. Choose the correct option.
  385. A magnetic flux of 5 x10 -4 Wb is associated with every 10 turns of a 500 turns coil. The electric current flowing through the wire is 5 A. What is the self-inductance of the coil?
  386. A rectangular loop of sides a and b is placed in xy plane. A very long wire is also placed in xy plane such that side of length a of the loop is parallel to the wire. The distance between the wire and the nearest edge of the loop is d. The mutual inductance of this system is proportional to
  387. A small coil of radius r is placed at the center of a large coil of radius R, where R >> r. The two coils are coplanar. The mutual inductance between the coils is proportional to
  388. A mutual inductor consists of two coils X and las shown in figure in which one quarter of the magnetic flux produced by X links with Y, giving a mutual inductance M. What will be the mutual inductance when Y is used as the primary?
  389. The coefficient of mutual inductance of two circuits A and B is 3 mH and their respective resistances are 10 Ω and 4 Ω . How much current should change in 0.02 s in circuit A, so that the induced current in B should be 0.0060 A?
  390. A circuit contains two inductors of self-inductance L 1 and L 2 in series (figure). If M is the mutual inductance, then the effective inductance of the circuit shown will be
  391. A long solenoid of length L, cross section A having N 1 turns has wound about its center a small coil of N 2 turns as shown in figure. The mutual inductance of two circuits is
  392. A bar magnet was pulled away from a hollow coil A as shown in figure. As the south pole came out of the coil, the bar magnet next to hollow coil B experienced a magnetic force
  393. As shown in the figure, P and Q are two coaxial conducting loops separated by some distance. When the switch S is closed, a clockwise current I P flows in P (as seen by E) and an induced current l Q1 flows in Q. The switch remains closed for a long time. When S is opened, a current I Q2 flows in Q. Then the directions of I Q1 and I Q2 (as seen by E) are
  394. Plane figures made of thin wires of resistance R = 50 milli ohm/meter are located in a uniform magnetic field perpendicular to the plane of the figures and which decrease at the rate dB/dt = 0.1 mT/s. Then currents in the inner and outer boundary are (The inner radius a = 10 cm and outer radius b = 20 cm)
  395. Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be
  396. A short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be,
  397. Shown in the figure is a circular loop of radius r and resistance R. A variable magnetic field of induction B = B 0 e -t is established inside the coil. If the key (K) is closed, the electrical power developed right after closing the switch is equal to
  398. A coil of wire having finite inductance and resistance has a conducting ring placed coaxially within it. The coil is connected to a battery at time t=0, so that a time dependent current I 1 (t) starts flowing through the coil. If l 2 (t) is the current induced in the ring and B(t) is the magnetic field at the axis of the coil due to l 1 (t), then as a function of time (t > 0), the product I 2 (t) B(t)
  399. The figure shows three circuits with identical batteries, inductors, and resistors. Rank the circuits according to the current (i 1 in circuit 1, i 2 in circuit 2, i 3 in circuit 3) through the battery (i) just after the switch is closed and (ii) a long time later, greatest first
  400. In Figures (a) and (b), two air-cored solenoids P and Q have been shown. They are placed near each other. In Figure (a), when I P , the current in P, changes at the rate of 5 A s -1 , an emf of 2 mV is induced in Q. The current in P is then switched off, and the current changing at 2A s -1 is fed through Q as shown in the figure. What emf will be induced in P?
  401. A simple pendulum with bob of mass m and conducting wire of length L swings under gravity through an angle 2 θ .The earth’s magnetic field component in the direction perpendicular to swing is, B. Maximum potential difference induced across the pendulum is
  402. A rectangular loop of wire with dimensions shown in figure is coplanar with a long wire carrying current I. The distance bet-ween the wire and the left side of the loop is r. The loop is pulled to the right as indicated. What are the directions of the induced current in the loop and the magnetic forces on the left and the right sides of the loop when the loop is pulled?
  403. A copper rod AB of length l is made to move with constant velocity v in a uniform magnetic field of induction B as shown in the figure. Then
  404. If the number of turns in a coil is doubled, Then self inductance will be
  405. A uniform but time varying magnetic field exists in cylindrical region and directed into the paper. If field increases with time and a positive charge placed at any point inside the region, then it moves
  406. A rectangular coil of 20 turns and area of cross-section 25 cm 2 has a resistance of 10 ohm. If a magnetic field which is perpendicular to the plane of the coil changes at a rate of 1000 tesla per sec, the current in the coil is :
  407. A coil having 500 square loops each of side 10 cm is placed normal to a magnetic field which increases at a rate of 1 T/s. The induced emf in volt is :
  408. A conducting square loop of side L and resistance R moves in its plane with a uniform velocity v perpendicular to one of its sides. A magnetic induction B, constant in time and space pointing perpendicular and into the plane of the loop exists everywhere. The current induced in the loop is :
  409. Magnetic flux through a circuit of resistance R changes by an amount ∆ ϕ in a time ∆ t . Total quantity of electric charge Q that passes any point in the circuit during the time ∆ t is represented by :
  410. If a coil of 40 turns and area 4.0 cm 2 is suddenly removed from a magnetic field, it is observed that a charge of 2.0 x 10 -4 C .flows into the coil. If the resistance of the coil is 80 Ω , the magnetic flux density in Wb/m 2 is …….
  411. A conducting square loop of side L and resistance R moves in its plane with a uniform velocity u perpendicular to one of its sides. A magnetic induction B constant in time and space, pointing perpendicular and into the plane at the loop exists everywhere with half the loop outside the field, as shown in Fig. The induced emf is :
  412. A coil having n turns and resistance R Ω is connected with a galvanometer of resistance 4R Ω . This combination is moved in time t seconds from a magnetic field W 1 weber to W 2 weber. The induced current in the circuit is :
  413. A rectangular loop has a sliding connector PQ of length l and resistance R Ω and it is moving with a speed v as shown. The setup is placed in a uniform magnetic field going into the plane of the paper. The three currents I 1 , I 2 and I are :
  414. In a coil of resistance 10 Ω , the induced current developed by changing magnetic flux through it, is shown in Fig. as a function of time. The magnitude of change in flux through the coil in weber is :
  415. A small coil of 10 turns is placed inside a solenoid of length 20 cm and 240 turns carry a current of 10 π A The area of small coil is 2.5 cm 2 and resistance 4.8 Ω then the current reduces to zero in 25 ms, the value of average induced current is :
  416. Eddy currents can be used to heat localized tissues of the human body. What is this branch of science referred to as?
  417. A wire is sliding on two parallel conducting rails placed at a separation of 1 m as shown in figure. Magnetic field 2 T exists in a direction perpendicular to rails. What force is necessary to keep the wire moving with a constant velocity of I cm/sec?
  418. A rod of length 50 cm moves with a speed of 10 cm/s, in a uniform magnetic field of strength 10 G at an angle of 30° with the field. The emf induced across the ends of the rod is :
  419. current of SA. A coil of radius· 1 cm having 100 turns and a total resistance of 20 Ω is placed inside the solenoid co-axially. The coil is connected to galvanometer. If current in the solenoid is reversed in direction. Find the charge flown through the galvanometer.
  420. A long solenoid has 500 turns. When a current of 2 ampere is passed through it, the resulting magnetic flux linked with each tum of the solenoid is 4 x 10 -3 Wb. The self-inductance of the solenoid is
  421. An inductor (L = 100 mH) a resistor (R = 100 Ω )and a battery (E = 100 V) are initially connected in series as shown in the Fig. 9.89. After a long time the battery is disconnected after short circuiting the points A and B. The current in the circuit 1 ms after the short circuit is :
  422. A coil of 40 henry inductance is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is :
  423. For a coil having L = 2 mH, current flow through it is given by l = t 2 e – 1 , then the time at which emf becomes zero, is :
  424. A solenoid having 500 turns and length 2 m has radius of 2 cm, then self inductance of solenoid is :
  425. A long solenoid has 1000 turns . When a current of 4 A flows through it, the magnetic flux linked with each turn of the solenoid is 4 x 10 -3 Wb .The self inductance of the solenoid is :
  426. Figure shows a circuit that contains three identical resistors with resistance R = 9.0 Ω each, two identical inductors with inductance L = 2.0 mH each, and an ideal battery with emf ε = 18 V The current ‘i’ through the battery just after the switch closed is :
  427. The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux ϕ linked with the primary coil is given by ϕ = ϕ 0 + 4 t , where ϕ is in weber, t is time in second and ϕ 0 is a constant, the output voltage across the secondary coil is :
  428. A square of side L meters lies in the x-y plane in a region, where the magnetic field is given by B = B 0 ( 2 i ^ + 3 j ^ + 4 k ^ ) T , where B 0 is constant. The magnitude of flux (in Wb) passing through the square is :
  429. The radius of a coil decreases steadily at the rate of 10 -2 m/s. A constant and uniform magnetic field of induction 10 -3 Wb/m 2 acts perpendicular to the plane of the coil. The radius of the coil when the induced emf in the coil is 1μV is :
  430. A student peddles a stationary bicycle. The pedals of the bicycle are attached to a 100 tum coil of area 0.10 m 2 . The coil rotates at half a revolution per second and it is placed in a uniform magnetic field of 0.10 T perpendicular to the axis of rotation of the coil. What is the maximum voltage generated in the coil?
  431. Magnetic field B in a cylindrical region of radius r varies according to the law B = B o t as shown in the figure. A fixed conducting loop ABCDA of resistance R is lying in the region as shown. The current flowing through the loop is
  432. The mutual inductance of the system of long straight conductor and the rectangular loop is
  433. A capacitor of capacitance C = 0.015 F is connected to parallel conducting rail and a conducting rod of mass m = 100 g and length 1m start to fall under gravity in vertical plane. A uniform magnetic field of 2T exist in space directed perpendicular to rod as shown in figure. Find acceleration of rod (m/s 2 ). (use g=10m/s 2 )
  434. Two coils have their mutual inductance 0.005 H. The current changes in the first coil according to equation i = 10 sin 100 π t A. The maximum value of emf in the second coil in volt, is
  435. A circular disc of radius 0.2 m is placed in a uniform magnetic field of induction 1 π    Wb m 2 in such a way that its axis makes an angle of 60 0 with B . The magnetic flux linked with the disc is
  436. The metallic ring shown in figure is suspended by an insulated thread and a bar magnet is held stationary inside the ring. If the magnet is quickly taken out of the ring to the right, then
  437. A copper rod AB of length 2m is moving in a uniform magnetic field of 1.5 T with a velocity of 3 m/s. The induced potential difference between ends A and B is
  438. A small bar magnet is allowed to fall vertically towards a copper ring which is held stationary with its plane horizontal. The axis of the ring passes through the mid-point of the bar magnet. If ‘a’ be the acceleration of the ring, then
  439. A small metallic ring of radius r (r <<< d) is made to move with velocity V towards an infinitely long current carrying conductor AB and the current induced in the ring is found to be 2 mA. If the same ring is made to move towards the same current carrying conductor AB with velocity 2V as shown in figure – (2), then induced current in the ring is Figure (1) and (2)
  440. A metallic ring is attached with the wall of a room. When the north pole of a magnet is brought near to it, the induced current in the ring will be (see from magnet side)
  441. An electron moves along the line AB, which lies in the same plane as a circular loop of conducting wires as shown in the diagram. What will be the direction of current induced, in the loop?
  442. A wire is bent to form the double loop shown in figure. There is a uniform magnetic field directed into the plane of the loop. If the magnitude of this field is decreasing, current will flow from
  443. Current flowing through a copper ring changes with time according to the graph shown in figure. If self inductance of the coil is 8 mH, the emf induced in the ring is
  444. A magnet is brought towards a coil speedily in the first case and slowly in the second case. Then the induced e.m.f./induced charge will be respectively
  445. A conducting ring is placed around the core of an electromagnet as shown in figure. When key K is pressed, the ring
  446. If a copper ring is moved quickly towards south pole of a powerful stationary bar magnet, then
  447. In the following figure, the magnet is moved towards the coil with a speed v and induced emf is e. If magnet and coil recede away from one another each moving with speed v, the induced emf in the coil will be
  448. An Aluminium ring B faces an electromagnet A. The current I through A can be altered. Then
  449. In the circuit shown, when a soft iron bar is quickly inserted into the inductor, the brightness of the bulb,
  450. The magnetic flux linked with a circuit of resistance 100 Ω increases from 10 wb to 60 wb. The amount of induced charge that flows in the circuit is (in coulombs)
  451. A circular coil of 500 turns of wire has an enclosed area of 0.1 m 2 per turn. It is kept pe{perpendicular to a magnetic field of induction 0.2 T and rotated by 180 0 about a diameter perpendicular to the field in 0.1 s. How much charge will pass when the coil is connected to a galvanometer with a combined resistance of 50 ohms?
  452. The total charge induced in a conducting loop when it is moved in magnetic field depends on
  453. In a magnetic field of 0.05 T, area of a coil changes from 101 cm 2 to 100 cm 2 without changing the resistance which is 2 Ω . The amount of charge that flow during this period is
  454. A thin circular ring of area A is perpendicular to uniform magnetic field of induction B. A small cut is made in the ring and a galvanometer is connected across the ends such that the total resistance of circuit is R. When the ring is suddenly squeezed to zero area, the charge flowing through galvanometer is
  455. In electromagnetic induction, the induced charge in a coil is independent of
  456. A flat circular coil of 10 cm radius has 200 turns of wire. The coil is connected to a capacitor of 20 μ F placed in a uniform magnetic field whose induction decreases at a rate of 0 .01 T s − 1 . Find the charge on capacitor.
  457. Magnetic flux ϕ (in weber) linked with a closed circuit of resistance 10 ohm varies with time / (in seconds) as ϕ = 5 t 2 − 4 t + 1 The induced electromotive force in the circuit at t = 0.2s is
  458. A loop, having area 20cm 2 , is made of thin copper wire. If is placed in a uniform magnetic field of induction 1.5 Tesla with its plane perpendicular to the field. If area of the loop increases to 30 cm 2 in 0.5 second, average emf induced in the loop is
  459. The magnetic flux linked with coil, in weber, is given by the equation, ϕ = 5 t 2 + 3 t + 16 The induced emf in the coil in the fourth second is
  460. A conducting wire frame is placed in a magnetic field which is directed into the paper. The magnetic field is increasing at a constant rate. The directions of induced current in wires AB and CD are
  461. A coil having an area A 0 is placed in a magnetic field which changes from B 0 to 4B 0 in a time interval t. The e.m.f. induced in the coil will be
  462. A circular ring, made of copper wire, has area of 30 cm 2 and resistance of 10 Ω . It is placed in a uniform magnetic field of induction 2 tesla with its plane perpendicular to the field. When the loop is rotated through an angle of θ about its diameter, 3 x 10 – 4 coulomb of charge flows through it. Then θ is
  463. In a coil of area 10 cm 2 and 10 turns, a magnetic field directed perpendicular to its plane and is changing at the rate of 10 8 gauss/second. The resistance of the coil is 20 ohm. The current in the coil will be
  464. A coil having 500 square loops each of side 10 cm is placed normal to a magnetic flux which increases at the rate of 1.0 tesla/second. The induced e.m.f. in volts is
  465. A square frame ABCD, made of copper wire is made to move with a velocity V parallel to the diagonal DB in a uniform magnetic field of induction ‘B’ as shown in figure. Induced potential difference between points A and D is 2 volt. Then select the correct option.
  466. A 50 turns circular coil has a radius of 3 cm. It is kept in a magnetic field acting normal to the area of the coil. The magnetic field B increases from 0.10 tesla to 0.35 tesla in 2 milliseconds. The average induced e.m.f. in the coil is
  467. A coil has 2000 turns and area of 70 cm 2 . The magnetic field perpendicular to the plane of the coil is 0.3 Wb/m 2 and takes 0.1 s to rotate through 180 0 . The value of the induced e.m.f. will be
  468. The magnetic field in a coil of 100 turns and 40 square cm area is increased from 1 T to 6 T in 2 s. The magnetic field is perpendicular to the coil. The e.m.f. generated in it is
  469. A coil having an area 2 m 2 is placed in a magnetic field which changes from 1Wb/m 2 to 4Wb/m 2 in a interval of 2 s. The e.m.f. induced in the coil will be
  470. A coil has 1000 turns and 500 cm 2 as its area. The plane of the coil is placed at right angles to a magnetic induction field of 2 × 10 − 4 Wb / m 2 . The coil is rotated through 180 0 in 0.2 s. The average e.m.f. induced in the coil, in millivolts, is
  471. A rectangular coil of 20 turns and area of cross-section 25 cm 2 has a resistance of 100 ohm. If a magnetic field which is perpendicular to the plane of the coil changes at the rate of 1000 tesla per second, the current in the coil is
  472. The coil of area 0.1 m 2 has 500 turns. After placing the coil in a magnetic field of strength 4 × 10 − 4 Wb / m 2 , if it is rotated through 90 0 in 0.1 s, the average emf induced in the coil is
  473. A conducting circular loop is placed in a uniform magnetic field of induction B tesla with its plane normal to the field. Now, radius of the loop starts shrinking at the rate (dr/dt). Then the induced e.m.f at the instant when the radius is r, is
  474. A conducting wire is moving towards right in a magnetic field B. The direction of induced current , in the wire is shown in the figure. The direction of magnetic field B will be
  475. The magnitude of the earth’s magnetic field at a place is B 0 and the angle of dip is δ . A horizontal conductor of length l lying along the magnetic north-south moves eastwards with a velocity v. The emf induced across the conductor is
  476. A long horizontal metallic rod with length along the east-west direction is falling under gravity. The potential difference between its two ends will
  477. A 10 metre long wire, kept in east-west direction, is falling with velocity 5 m/s pe{perpendicular to the field 0 . 3 × 10 – 4 Wb/m 2 . The induced e.m.f. across the terminal will be
  478. An aeroplane in which the distance between the tips of wings is 50 m is flying horizontally with a speed of 360 km/h over a place where the vertical components of earth magnetic field is 2 . 0 × 10 – 4 Wb / m 2 The potential difference between the tips of wings would be
  479. A copper disc of radius 0.1 m is rotated about its centre with 10 revolutions per second in a uniform magnetic field of 0.1 T with its plane perpendicular to the field. The e.m.f. induced across the radius of disc is
  480. A coil of area 80 square cm and 50 turns is rotating with 2000 revolutions per minute about an axis perpendicular to a magnetic field of 0.05 T. The maximum value of the e.m.f. developed in it is
  481. A wheel with ten metallic spokes each 0.50 m long is rotated with a speed of 120 rev/min in a plane normal to the earth’s magnetic field at the place. If the magnitude of the field is 0.4 gauss, the induced e.m.f. between the axle and the rim of the wheel is equal to
  482. A metal rod of length 2 m is rotating with an angular velocity of 100 rad/s in a plane perpendicular to a uniform magnetic field of 0.3 T. The potential difference between the ends of the rod is
  483. A rod of length 20 cm is rotating with angular speed of 100 rps in a magnetic field of strength 0.5 T about its one end. What is the potential difference between two ends of the rod?
  484. A rectangular coil of 300 turns has an average area of average area of 25 cm × 10 cm . The coil rotates with a speed of 50 cps in a uniform magnetic field of strength 4 × 10 – 2 T about an axis perpendicular of the field. The peak value of the induced e.m.f. is (in volt)
  485. A conducting rod of length 2 l is rotating with constant angular speed ω about its perpendicular bisector. A uniform magnetic field B exists parallel to the axis of rotation. The e.m.f. induced between two ends of the rod is
  486. As shown in the figure, a metal rod makes contact and complete the circuit. The circuit is perpendicular to the magnetic field with B = 0.15 T. If the resistance is 3 Ω force needed to move the rod as indicated with a constant speed of 2 m/s is
  487. Consider the situation shown in the figure. The wire AB is sliding on the fixed rails with a constant velocity V. lf the wire AB is replaced by semicircular wire, the magnitude of the induced current will
  488. One conducting U tube can slide inside another as shown in figure, maintaining electrical contacts between the tubes. The magnetic field B is perpendicular to the plane of the figure. If each tube moves towards the other at a constant sped v, then the emf induced in the circuit in terms of B, l and v, where I is the width of each tube, will be
  489. A square metallic wire loop of side 0.1 m and resistance of 1 Ω is moved with a constant velocity in a magnetic field of 2 Wb/m 2 as shown in figure. The magnetic field B is perpendicular to the plane of the loop. This loop is connected to a network of resistances. What should be the velocity of loop so as to have a steady current of 1 mA in loop?
  490. A wire cd of length l and mass m is sliding without friction on conducting rails ax and by as shown. The vertical rails are connected to each other with a resistance R between a and b. A uniform magnetic field B is applied perpendicular to the plane abcd such that cd moves with a constant velocity of
  491. A conductor ABOCD moves along its bisector with a velocity of 1 m/s through a perpendicular magnetic field of 1 Wb/m 2 , as shown in fig. If all the four sides are of 1 m length each, then the induced emf between points A and D is
  492. Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be
  493. The back e.m.f. induced in a coil, when current changes from 1 ampere to zero in one millisecond, is 4 volts. The self-inductance of the coil is
  494. A copper rod of length l is rotated about one end perpendicular to the magnetic field B with constant angular velocity ω . The induced e.m.f. between the two ends is
  495. An e.m.f. of 5 V is produced by a self-inductance, when the current changes at a steady rate from 3 A to 2 A in 1 millisecond. The value of self-inductance is
  496. Average energy stored in a pure inductance L when a current i flows through it, is
  497. A 50 mH coil carries a current of 2 A. The energy stored, in joules, is
  498. The coefficient of self-inductance of a solenoid is 0.18 mH. If a core of soft iron of relative permeability 900 is inserted, then the coefficient of self-inductance will become nearly
  499. A coil of wire of a certain radius has 600 turns and a self-inductance of 108 mH. The self-inductance of a 2 nd similar coil of 500 turns will be
  500. When the number of turns in a coil is doubled without any change in the length of the coil, its self-inductance
  501. An e.m.f. of 12 volts is induced in a given coil when the current in it changes at the rate of 48 amperes per minute. The self-inductance of the coil is
  502. An e.m.f. of 100 millivolts is induced in a coil when the current in another nearby coil becomes 10 ampere from zero in 0.1 second. The coefficient of mutual induction between the two coils will be
  503. In a coil of self-inductance 0.5 henry, the current varies at a constant rate from zero to 10 amperes in 2 seconds. The e.m.f. generated in the coil is
  504. The energy stored in a 50 mH inductor carrying a current of 4 A will be
  505. The mutual inductance between a primary and secondary circuits is 0.5 H. The resistances of the primary and the secondary circuits are 20 ohms and 5 ohms, respectively. To generate a current of 0.4 A in the secondary, current in the primary must be changed at the rate of
  506. A varying current in a coil changes from 10 A to zero in 0.5 s. If average e.m.f. induced in the coil is 220 volts, the self-inductance of coil is
  507. A 100 mH coil carries a current of 1 A. Energy stored in its magnetic field is
  508. A varying current at the rate of 3 A/s in a coil generates an e.m.f. of 8 mV in a nearby coil. The mutual inductance of the two coils is
  509. The self-inductance of a straight conductor is
  510. If a current of 10 A flows in one second through a coil, and the induced e.m.f. is 10 V, then the self-inductance of the coil is
  511. An e.m.f. of 12 V is produced in a coil when the current in it changes at the rate of 45 A/min. The inductance of the coil is
  512. If a change in current of 0.01 A in one coil produces a change in magnetic flux of 1 . 2 × 10 – 2 Wb in the other coil, then the mutual inductance of the two coils, in henry is
  513. The coefficient of mutual inductance of two coils is 6 mH. If the current flowing in one is 2 A, then the induced e.m.f. in the second coil will be
  514. An air core solenoid has 1000 turns and is one metre long. Its cross-sectional area is 10 cm 2 . Its self-inductance is
  515. A coil of 100 turns carries a current of 5 A and creates a magnetic flux of 10 – 5 T m – 2 per turn. The value of its inductance Z will be
  516. Two identical induction coils each of inductance L joined in series are placed very close to each other such that the winding direction of one is exactly opposite to that of the other. What is the net inductance?
  517. A coil resistance 20 Ω and inductance 5 H is connected with a 100 V battery. Energy stored in the coil will be
  518. The current in a coil decreases from 1 A to 0.2 A in 10 s. Calculate the coefficient of self-inductance, if induced emf is 0.4 volt.
  519. Two inductors L 1 and L 2 are connected in parallel and a time varying current flows as shown. The ratio of currents i 1 /i 2 at any time / is
  520. An ideal coil of 10 H is joined in series with a resistance of 5 Ω and a battery of 5 V. 2 s after joining, the current flowing in ampere in the circuit will be
  521. A coil has an inductance of 2.5 H and a resistance of 0 . 5 Ω If the coil is suddenly connected across a 6.0 V battery then the time required for the current to rise 0.63 of its final value is
  522. The equivalent inductance of two inductances is 2.4 H when connected in parallel and 10 H when connected in series. The difference between the two inductances is
  523. The resistance in the following circuit is increased at a particular instant. At this instant the value of resistance is 10 Ω . The current in the circuit will be now
  524. The current in an LR circuit builds up to 3 th 4 of its steady state value in 4 s. The time constant of this circuit is
  525. In series with 20 Ω resistor, & 5 H inductor is placed. To the combination an e.m.f. of 5 V is applied. What will be the rate of increase of current at t = 0.25 s?
  526. In the circuit shown, X is joined to Y for a long time and then X is joined to Z. The total heat produced in R 2 is
  527. In which of the following circuits is the current maximum just after the switch S is closed?
  528. In the circuit shown, sliding contact is moving with uniform velocity towards right. Its value at some instance is 12 Ω . The current in the circuit at this instant of time will be
  529. Two coils of self-inductances 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is
  530. As a result of change in the magnetic flux linked to the closed loop shown in the figure, an emf V volt is induced in the loop. The work done (joules) in taking a charge Q coulomb once along the loop is
  531. A coil is wound on a transformer of rectangular cross-section. If all the linear dimensions of the transformer are increased by a factor 2 and the number of turns per unit length of the coil remain the same, the self-inductance is increased by a factor of
  532. A coil of self-inductance 50 henry is joined to the terminals of a battery of e.m.f. 2 volts through a resistance of 10 ohm and a steady current is flowing through the circuit. If the battery is now disconnected, the time in which the current will decay to 1/e of its steady value is
  533. The coefficients of mutual inductance when magnetic flux changes by 2 × 10 − 2 Wb and current changes by 0.01 A, will be
  534. A metal rod of resistance 20 Ω is fixed along a diameter of a conducting ring of radius 0.1 m and lies in an x-y plane. There is a magnetic field B = ( 50 T ) k ^ . The ring rotates with an angular velocity ω = 20 rad / s about its axis. An external resistance of 10 Ω is connected across the centre of the ring and rim. The current through external resistance is
  535. A current of 2A is increasing at a rate of 4 A/s through a coil of inductance 2H. The energy stored in the inductor per unit time is
  536. An inductor of 2H and a resistance of 10 Ω are connected in series with a battery of 5 V. The initial rate of change of current is
  537. A coil of inductance 8.4 mH and resistance 6 Ω is connected to a 12 V battery. The current in the coil is 1.0 A at approximately the time
  538. The magnetic field in the cylindrical region shown in figure increases at a constant rate of 20 mT/s. Each side of the square loop ABCD has a length of 1 cm and resistance of 4 Ω . Find the current in the wire AB if the switch S is closed
  539. How much length of a very thin wire is required to obtain a solenoid of length l 0 and inductance L?
  540. what is the mutual inductance of a two-loop system as shown with centre separation l ?
  541. A conducting ring of radius 1 m is placed in an uniform magnetic field B of 0.01 T oscillating with frequency 100 Hz with its plane at right angles to B. What will be the induced electric field?
  542. Statement 1: Self-inductance is called the inertia of electricity. Statement 2: Self-inductance is the phenomenon, according to which an opposing induced e.m.f. is produced in a coil as a result of change in current or magnetic flux linked in the coil.
  543. A uniform but time-varying magnetic field B(t) exists in a circular region of radius a and is directed into the plane of the paper, as shown. The magnitude of the induced electric field at point P at a distance r from the centre of the circular region
  544. Statement 1: When two coils are wound on each other, the mutual induction between the coils is maximum. Statement 2: Mutual induction does not depend on the orientation of the coils.
  545. Statement 1: The self-inductance (L) is equal to ϕ (magnetic flux) / i (current). Statement 2: When current increases, self-inductance increases.
  546. The current flowing in a coil of self-inductance 0.4 mH is increased by 250 mA in 0.1 s. The e.m.f. induced will be
  547. Two pure inductors each of self-inductance L are connected in parallel but are well separated from each other. The total inductance is
  548. A coil and a bulb are connected in series with a dc source. When an external agent is inserting a soft iron core in the coil ,
  549. 5 cm long solenoid having 10 ohm resistance and 5 mH inductance is joined to a 10 volt battery. At steady state the current through the solenoid in ampere will be
  550. A coil of 100 turns carries a current of 5 mA and creates a magnetic flux of 10 − 5 weber. The inductance is
  551. If the current 30 A flowing in the primary coil is made zero in 0.1 s, the emf induced in the secondary coil is 1.5 V. The mutual inductance between the coils is
  552. In circular coil, when no. of turns is doubled and resistance becomes 1 4 th of initial, then inductance becomes
  553. Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon
  554. when the current change from + 2 A to − 2 A 2 A in 0.05 s, an e.m.f. of 8 V is induced in a coil. The coefficient of self-induction of the coil is
  555. A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 radians per second. If the horizontal component of earth’s magnetic field is 0.2 × 10 − 4 T then the e.m.f. developed between the two ends of the conductor is
  556. A small square loop of wire of side l is placed inside a large square loop of wire of side L ( L > > l ) . The loops are coplanar and their centre coincide. The mutual inductance of the system is proportional to
  557. PQ is an infinite current carrying conductor. AB and CD are smooth conducting rods on which a conductor EF moves with constant velocity v as shown. The force needed to maintain constant speed of EF is(neglect the weight of conductor)
  558. In the given figure two concentric cylindrical region in which time varying magnetic field is present as shown. From the center to radius R magnetic field is perpendicular into the plane varying as dB/dt = 2k 0 and in a region from R to 2R magnetic field is perpendicular out of the plane varying as dB/dt = 4k 0 .Find the induced emf across an arc AB of radius 3R.
  559. The diagram shows a solenoid carrying time varying current l = l 0 t. On the axis of the solenoid, a ring has been placed. The mutual inductance of the ring and the solenoid is M and the self-inductance of the ring is L. If the resistance of the ring is R then maximum current which can flow through the ring is
  560. An inductor coil stores 32 J of magnetic field energy and dissipates energy as heat at the rate of 320 W when a current of 4 amp is passed through it. Find the time constant of the circuit when it is formed across an ideal battery.
  561. Four different uniform and constant magnetic fields B 1 = B 0 k ^ , B 2 = 2 B 0 k ^ , B 3 = 3 B 0 k ^ and B 4 = 4 B 0 k ^ exist in first, second, third and fourth quadrant respectively of x-y plane as shown in figure. A square wireframe PQRS of one side I and total resistance R lying in x-y plane is moving with velocity v = v 0 i ^ such that its centre lies on x-axis and side PQ is parallel to x-axis. B 0 and v 0 are positive constants. Then the magnitude of current induced in the square loop at the instant its centre lies of origin is
  562. In the circuit shown, sliding contact is moving with uniform velocity towards right. Its value at some instance is 12 Ω . The current in the circuit at this instant of time will be
  563. A square wire loop of 10.0 cm side lies at right angles to a uniform magnetic field of 7T. A 10 V light bulb is in a series with the loop as shown in the figure. The magnetic field is decreasing steadily to zero over a time interval ∆ t . For what value of Δ t in × 10 – 3 sec , the bulb will shine with fuIl brightness?
  564. Two long, horizontal pair of rails shown in the figure is connected using resistance R. The distance between the rails is l, the electrical resistance of the rails is negligible. A conducting wire of mass m and length l can slide without friction on the pair of rails, in a vertical, homogeneous magnetic field of induction B. A force of magnitude F 0 is exerted for sufficiently long time onto the conducting wire, so that the speed of the wire becomes nearly constant. The force F 0 is now removed at a certain point P. What distance (in x 10 2 m) does the conducting wire cover on rails from point P before stopping? (Given: F 0 = 20 N , m = 1.0 gm , R = 0.01 Ω , l = 10 cm , B=0.1T)
  565. A circular coil of wire consists of exactly 100 turns with a total resistance of 0.20 Ω . The area of the coils is 100 cm 2 . The coil is kept in a uniform magnetic field B as shown in the figure. The magnetic field is increased at a constant rate of 2 T/s. The induced current in the coil in A is .
  566. A pair of parallel horizontal conducting rails of negligible resistance shorted at one end is fixed on a table. The distance between the rails is l. A conducting massless rod of resistance R can slide on the rails frictionlessly. The rod is tied to a massless string which passes over a pulley fixed to the edge of the table. A mass m, tied to the other end of the string, hangs vertically. A constant magnetic field B exists perpendicular to the table. If the system is released from rest, calculate the acceleration of the mass at the instant when the velocity of the rod is half the terminal velocity (in m/s 2 ).
  567. A uniforrn magnetic field B = 0.5 T exists in a circular region of radius R=5m.A loop of radius R = 5 m encloses the magnetic field at t = 0 and then pulled at uniform speed v = 2 m/s in the plane of the paper. The induced emf in the loop at time t = 3 sec (in V) is
  568. A coil of mean area 500 cm 2 and having 1000 turns is held perpendicular to a uniform field of 0.4 gauss. the coil is turned through 180 o in 1/10 second. The average induced emf (in V) is
  569. A circular copper disc 10 cm in radius rotates at 20 π rads − 1 about an axis through its centre and perpendicular to the disc. A uniform magnetic field of 0.2 T acts perpendicular to the disc. What is the induced current (in A), if the resistance of 2 Ω is connected in between axis and rim of the disc.
  570. A closed coil having 20 turns, area of cross-section 1 cm 2 and negligible resistance are connected to a ballistic galvanometer of resistance 30 ohms. If the normal of the coil is inclined at 60 o to the direction of a magnetic field of intensity 1.5 Wb/m 2 , the coil is quickly pulled out of the field to a region of zero magnetic field, the charge (in μ C) passed through the galvanometer is .
  571. A square wire loop with side L = 1 .0 m sides is perpendicular to a uniform magnetic field, with half the area of the loop in the field as shown in figure. The resistance of the loop is 35 Ω and the loop contains an ideal battery with emf ε = 6.0 V. If the magnitude of the field varies with time according to B = 5.0 – 2.0t, with B in tesla and t in seconds, what is current (in A) around the loop?
  572. Identify the factor on which self-inductance of a coil does not depend.
  573. An induced emf is produced when a magnet is plunged into a coil. The strength of the induced emf is independent of
  574. Coefficient of mutual induction between 2 coils is 0.4 H. If a current of 4A in the primary is cut off in 1/15000 second, the emf induced in the secondary is
  575. Find the average induced voltage in a coil of an area 500 cm 2 and having 1000 turns, when it is turned through 180 0 in 0. 1 s. It is also given that the coil is initially placed perpendicularly to a uniform field of 0.4 gauss.
  576. On what factors does the coefficient of mutual inductance of two coils depends?
  577. In electromagnetic induction, the induced e.m.f. in a coil is independent of
  578. Lenz’s law is consequence of the law of conservation of
  579. The magnetic flux through a circuit of resistance R changes by an amount Δϕ in time Δt , Then the total quantity of electric charge Q, which passing during this time through any point of the circuit is given by
  580. In electromagnetic induction, the induced charge in a coil is independent of
  581. A metallic ring is attached with the wall of a room. When the north pole of a magnet is brought near to it, the induced current in the ring will be
  582. The magnetic flux linked with a coil is given by an equation ϕ (in webers) = 8 t 2 + 3 t + 5 . The induced e.m.f. in the coil at the four seconds will be
  583. A coil having an area A 0 is placed in a magnetic field which changes from B 0 to 4B 0 in a time interval t. The e.m.f. induced in the coil will be
  584. The current flowing in two coaxial coils in the same direction. On increasing the distance between the two, the electric current will
  585. A copper ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet while it is passing through the ring is
  586. A magnet is brought towards a coil (i) speedly (ii) slowly then the induced e.m.f./induced charge will be respectively
  587. The direction of induced e.m.f. during electromagnetic induction is given by
  588. A coil having 500 square loops each of side 10 cm is placed normal to a magnetic flux which increases at the rate of 1.0 tesla/second. The induced e.m.f. in volts is
  589. A coil has 2000 turns and area of 70cm 2 . The magnetic field perpendicular to the plane of the coil is 0.3 Wb/m 2 and takes 0.1sec to rotate through 180 o . The value of the induced e.m.f. will be
  590. Two different loops are concentric and lie in the same plane. The current in the outer loop is clockwise and increasing with time. The induced current in the inner loop then, is
  591. According to Faraday’s law of electromagnetic induction
  592. The unit of magnetic flux is
  593. Lenz’s law gives
  594. The direction of induced current is such that it opposes the very cause that has produced it. This is the law of
  595. In a circuit with a coil of resistance 2 ohms, the magnetic flux changes from 2.0 Wb to 10.0 Wb in 0.2 second. The charge that flows in the coil during this time is
  596. A circular coil of 500 turns of wire has an enclosed area of 0.1 m 2 per turn. It is kept perpendicular to a magnetic field of induction 0.2 T and rotated by 180° about a diameter perpendicular to the field in 0.1 sec. How much charge will pass when the coil is connected to a galvanometer with a combined resistance of 50 ohms
  597. A metallic ring connected to a rod oscillates freely like a pendulum. If now a magnetic field is applied in horizontal direction so that the pendulum now swings through the field, the pendulum will
  598. To induce an e.m.f. in a coil, the linking magnetic flux
  599. A coil of 40 Ω resistance has 100 turns and radius 6 mm is connected to ammeter of resistance of 160 ohms. Coil is placed perpendicular to the magnetic field. When coil is taken out of the field, 32 μ C charge flows through it. The intensity of magnetic field will be
  600. Faraday’s laws are consequence of conservation of
  601. The magnetic flux linked with a coil, in webers, is given by the equations ϕ = 3 t 2 + 4 t + 9 . Then the magnitude of induced e.m.f. at t = 2 second will be
  602. If a coil of metal wire is kept stationary in a non-uniform magnetic field, then
  603. In the diagram shown if a bar magnet is moved along the common axis of two single turn coils A and B in the direction of arrow
  604. The formula for induced e.m.f. in a coil due to change in magnetic flux through the coil is (here A = area of the coil, B = magnetic field)
  605. A magnet is dropped down an infinitely long vertical copper tube
  606. The magnetic flux linked with a coil at any instant ‘t’ is given by ϕ = 5t 3 – 100t + 300, the e.m.f. induced in the coil at t = 2 second is
  607. An aluminium ring B faces an electromagnet A. The current I through A can be altered
  608. A coil has 1,000 turns and 500 cm 2 as its area. The plane of the coil is placed at right angles to a magnetic induction field of 2 × 10 − 5 Wb / m 2 . The coil is rotated through 180 o in 0.2 seconds. The average e.m.f. induced in the coil, in milli-volts, is
  609. A magnet NS is suspended from a spring and while it oscillates, the magnet moves in and out of the coil C. The coil is connected to a galvanometer G. Then as the magnet oscillates,
  610. A coil having n turns and resistance RΩ is connected with a galvanometer of resistance 4 RΩ . This combination is moved in time t seconds from a magnetic field W 1 weber to W 2 weber. The induced current in the circuit is
  611. If a copper ring is moved quickly towards south pole of a powerful stationary bar magnet, then
  612. The coil of area 0.1 m 2 has 500 turns. After placing the coil in a magnetic field of strength 4 × 10 − 4 Wb / m 2 , if rotated through 90 o in 0.1 s, the average emf induced in the coil is
  613. The magnetic flux linked with coil, in weber is given by the equation, ϕ = 5 t 2 + 3 t + 16 . The induced emf in the coil in the fourth second is
  614. Magnetic flux in a circuit containing a coil of resistance 2 Ω changes from 2.0 Wb to 10 Wb in 0.2 sec. The charge passed through the coil in this time is
  615. The diagram below shows two coils A and B placed parallel to each other at a very small distance. Coil A is connected to an ac supply. G is a very sensitive galvanometer. When the key is closed
  616. A rectangular coil ABCD is rotated anticlockwise with a uniform angular velocity about the axis shown in diagram below. The axis of rotation of the coil as well as the magnetic field B are horizontal. The induced e.m.f. in the coil would be maximum when
  617. Two rails of a railway track insulated from each other and the ground are connected to a milli voltmeter. What is the reading of voltmeter, when a train travels with a speed of 180 km/hr along the track. Given that the vertical component of earth’s magnetic field is 0.2 × 10 − 4 weber / m 2 and the rails are separated by 1 metre
  618. A conductor of 3 m in length is moving perpendicularly to magnetic field of 10 -3 tesla with the speed of 10 2 m/s, then the e.m.f. produced across the ends of conductor will be
  619. When a wire loop is rotated in a magnetic field, the direction of induced e.m.f. changes once in each
  620. A metal conductor of length 1m rotates vertically about one of its ends at angular velocity 5 radians per second. If the horizontal component of earth’s magnetic field is 0 .2 × 10 − 4 T , then the e.m.f. developed between the two ends of the conductor is
  621. A player with 3 m long iron rod runs towards east with a speed of 30 km/hr. Horizontal component of earth’s magnetic field is 4 × 10 − 5 Wb / m 2 . If he is running with rod in horizontal and vertical positions, then the potential difference induced between the two ends of the rod in two cases will be
  622. A coil of area 80 square cm and 50 turns is rotating with 2000 revolutions per minute about an axis perpendicular to a magnetic field of 0.05 Tesla. The maximum value of the e.m.f. developed in it is
  623. A conducting rod of length l is falling with a velocity v perpendicular to a uniform horizontal magnetic field B. The potential difference between its two ends will be
  624. A conducting wire is moving towards right in a magnetic field B. The direction of induced current in the wire is shown in the figure. The direction of magnetic field will be
  625. The current carrying wire and the rod AB are in the same plane. The rod moves parallel to the wire with a velocity v. Which one of the following statements is true about induced emf in the rod
  626. A two metre wire is moving with a velocity of 1 m/sec perpendicular to a magnetic field of 0.5 weber/m 2 . The e.m.f. induced in it will be
  627. A long horizontal metallic rod with length along the east-west direction is falling under gravity. The potential difference between its two ends will
  628. A conducting wire is dropped along east-west direction, then
  629. The magnetic induction in the region between the pole faces of an electromagnet is 0.7 weber/m 2 . The induced e.m.f. in a straight conductor 10 cm long, perpendicular to B and moving perpendicular both to magnetic induction and its own length with a velocity 2 m/sec is
  630. A straight conductor of length 0.4 m is moved with a speed of 7 m/s perpendicular to the magnetic field of intensity of 0.9 Wb/m 2 . The induced e.m.f. across the conductor will be
  631. A conducting square loop of side l and resistance R moves in its plane with a uniform velocity v perpendicular to one of its sides. A magnetic induction B constant in time and space, pointing perpendicular and into the plane at the loop exists everywhere with half the loop outside the field, as shown in figure. The induced e.m.f. is
  632. A coil of N turns and mean cross-sectional area A is rotating with uniform angular velocity ω about an axis at right angle to uniform magnetic field B. The induced e.m.f. E in the coil will be
  633. A wheel with ten metallic spokes each 0.50 m long is rotated with a speed of 120 rev/min in a plane normal to the earth’s magnetic field at the place. If the magnitude of the field is 0.4 Gauss, the induced e.m.f. between the axle and the rim of the wheel is equal to
  634. A metal rod of length 2 m is rotating with an angular velocity of 100 rad/sec in a plane perpendicular to a uniform magnetic field of 0.3 T. The potential difference between the ends of the rod is
  635. The wing span of an aeroplane is 20 metre. It is flying in a field, where the vertical component of magnetic field of earth is 5 × 10 –5 tesla, with velocity 360 km/h. The potential difference produced between the blades will be
  636. A horizontal straight conductor kept in north-south direction falls under gravity, then
  637. A rectangular coil of 300 turns has an average area of average area of 25   c m × 10   c m . The coil rotates with a speed of 50 cps in a uniform magnetic field of strength 4 × 10 − 2 T about an axis perpendicular of the field. The peak value of the induced e.m.f. is (in volt)
  638. A rod of length 20 cm is rotating with angular speed of 100 rps in a magnetic field of strength 0.5 T about it’s one end. What is the potential difference between two ends of the rod
  639. A circular metal plate of radius R is rotating with a uniform ω angular velocity with its plane perpendicular to a uniform magnetic field B. Then the emf developed between the centre and the rim of the plate is
  640. A circular coil of mean radius of 7 cm and having 4000 turns is rotated at the rate of 1800 revolutions per minute in the earth’s magnetic field (B = 0.5 gauss), the maximum e.m.f. induced in coil will be
  641. The magnitude of the earth’s magnetic field at a place is B 0 and the angle of dip is δ . A horizontal conductor of length l lying along the magnetic north-south moves eastwards with a velocity v. The emf induced across the conductor is
  642. A 50 mH coil carries a current of 2 ampere. The energy stored in joules is
  643. An e.m.f. of 5 volt is produced by a self inductance, when the current changes at a steady rate from 3 A to 2 A in 1 millisecond. The value of self inductance is
  644. A coil is wound as a transformer of rectangular cross-section. If all the linear dimensions of the transformer are increased by a factor 2 and the number of turns per unit length of the coil remain the same, the self inductance increased by a factor of
  645. A solenoid has 2000 turns wound over a length of 0.30 metre. The area of its cross-section is 1 .2 × 10 − 3 m 2 . Around its central section, a coil of 300 turns is wound. If an initial current of 2 A in the solenoid is reversed in 0.25 sec, then the e.m.f. induced in the coil is
  646. The equivalent quantity of mass in electricity is
  647. In what form is the energy stored in an inductor or A coil of inductance L is carrying a steady current i. What is the nature of its stored energy
  648. The coefficient of self inductance of a solenoid is 0.18 mH. If a crode of soft iron of relative permeability 900 is inserted, then the coefficient of self inductance will become nearly
  649. In a transformer, the coefficient of mutual inductance between the primary and the secondary coil is 0.2 henry. When the current changes by 5 ampere/second in the primary, the induced e.m.f. in the secondary will be
  650. The mutual inductance between two coils is 1.25 henry. If the current in the primary changes at the rate of 80 ampere/second, then the induced e.m.f. in the secondary is
  651. When the number of turns in a coil is doubled without any change in the length of the coil, its self inductance becomes
  652. The average e.m.f. induced in a coil in which the current changes from 2 ampere to 4 ampere in 0.05 second is 8 volt. What is the self inductance of the coil ?
  653. If a current of 3.0 amperes flowing in the primary coil is reduced to zero in 0.001 second, then the induced e.m.f. in the secondary coil is 15000 volts. The mutual inductance between the two coils is
  654. An e.m.f. of 12 volts is induced in a given coil when the current in it changes at the rate of 48 amperes per minute. The self inductance of the coil is
  655. A closely wound coil of 100 turns and area of cross-section 1 cm 2 has a coefficient of self-induction 1 mH. The magnetic induction in the centre of the core of the coil when a current of 2A flows in it, will be
  656. Two circuits have coefficient of mutual induction of 0.09 henry. Average e.m.f. induced in the secondary by a change of current from 0 to 20 ampere in 0.006 second in the primary will be
  657. In the following circuit, the bulb will become suddenly bright if
  658. Two pure inductors each of self inductance L are connected in parallel but are well separated from each other. The total inductance is
  659. A coil and a bulb are connected in series with a dc source, a soft iron core is then inserted in the coil. Then
  660. Self induction of a solenoid is
  661. Mutual inductance of two coils can be increased by
  662. The unit of inductance is
  663. The self inductance of a coil is 5 henry, a current of 1 amp change to 2 amp within 5 second through the coil. The value of induced e.m.f. will be
  664. The current flowing in a coil of self inductance 0.4 mH is increased by 250 mA in 0.1 sec. The e.m.f. induced will be
  665. 5 cm long solenoid having 10 ohm resistance and 5 mH inductance is joined to a 10 volt battery. At steady state the current through the solenoid in ampere will be
  666. When current in a coil changes to 2 ampere from 8 ampere in 3 × 10 − 3   second , the e.m.f. induced in the coil is 2 volt. The self inductance of the coil in millihenry is
  667. An ideal coil of 10 henry is joined in series with a resistance of 5 ohm and a battery of 5 volt. 2 second after joining, the current flowing in ampere in the circuit will be
  668. The number of turns of primary and secondary coils of a transformer are 5 and 10 respectively and the mutual inductance of the transformer is 25 henry. Now the number of turns in the primary and secondary of the transformer are made 10 and 5 respectively. The mutual inductance of the transformer in henry will be
  669. The inductance of a coil is 60   μH . A current in this coil increases from 1.0 A to 1.5 A in 0.1 second. The magnitude of the induced e.m.f. is
  670. An e.m.f. of 100 millivolts is induced in a coil when the current in another nearby coil becomes 10 ampere from zero in 0.1 second. The coefficient of mutual induction between the two coils will be
  671. A circular coil of radius 5 cm has 500 turns of a wire. The approximate value of the coefficient of self induction of the coil will be
  672. The self inductance of a coil is L. Keeping the length and area same, the number of turns in the coil is increased to four times. The self inductance of the coil will now be
  673. In a coil of self inductance 0.5 henry, the current varies at a constant rate from zero to 10 amperes in 2 seconds. The e.m.f. generated in the coil is
  674. The mutual inductance between a primary and secondary circuits is 0.5 H. The resistances of the primary and the secondary circuits are 20 ohms and 5 ohms respectively. To generate a current of 0.4 A in the secondary, current in the primary must be changed at the rate of
  675. The average e.m.f. induced in a coil in which a current changes from 0 to 2 A in 0.05 s is 8 V. The self inductance of the coil is
  676. If the current is halved in a coil, then the energy stored is how much times the previous value
  677. Which of the following is wrong statement
  678. A 100 mH coil carries a current of 1 ampere. Energy stored in its magnetic field is
  679. A varying current in a coil changes from 10 amp to zero in 0.5 sec. If average EMF is induced in the coil is 220 volts, the self inductance of coil is
  680. When the number of turns and the length of the solenoid are doubled keeping the area of cross-section same, the inductance
  681. The mutual inductance of an induction coil is 5H. In the primary coil, the current reduces from 5A to zero in 10 -3 s. What is the induced emf in the secondary coil
  682. What is the coefficient of mutual inductance when the magnetic flux changes by 2 × 10 − 2 Wb and change in current is 0.01A
  683. Pure inductance of 3.0 H is connected as shown below. The equivalent inductance of the circuit is
  684. When the current through a solenoid increases at a constant rate, the induced current
  685. The inductance of a solenoid 0.5 m long of cross-sectional area 20 cm 2 and with 500 turns is
  686. An average induced e.m.f. of 1V appears in a coil when the current in it is changed from 10A in one direction to 10 A in opposite direction in 0.5 sec. Self-inductance of the coil is
  687. Energy stored in a coil of self inductance 40mH carrying a steady current of 2 A is
  688. Two coils A and B having turns 300 and 600 respectively are placed near each other, on passing a current of 3.0 ampere in A, the flux linked with A is 1 .2 × 10 − 4   weber and with B it is 9 .0 × 10 − 5   weber . The mutual inductance of the system is
  689. Find out the e.m.f. produced when the current changes from 0 to 1 A in 10 second, given L = 10 μ H
  690. The current in a coil of inductance 5 H decreases at the rate of 2 A/s. The induced e.m.f. is
  691. Two circuits have mutual inductance of 0.1 H. What average e.m.f. is induced in one circuit when the current in the other circuit changes from 0 to 20 A in 0.02 s
  692. The coefficient of mutual inductance of two coils is 6 mH. If the current flowing in one is 2 ampere, then the induced e.m.f. in the second coil will be
  693. Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon
  694. When the current change from + 2A to – 2A in 0.05 second, an e.m.f. of 8 V is induced in a coil. The coefficient of self-induction of the coil is
  695. A coil of N = 100 turns carries a current I = 5 A and creates a magnetic flux ϕ = 10 − 5 Tm − 2 per turn. The value of its inductance L will be
  696. Eddy currents are used in
  697. The adjoining figure shows two bulbs B 1 and B 2 resistor R and an inductor L. When the switch S is turned off
  698. Plane of eddy currents makes an angle with the plane of magnetic lines of force equal to
  699. A transformer is based on the principle of
  700. The pointer of a dead-beat galvanometer gives a steady deflection because
  701. Which of the following is not an application of eddy currents
  702. The working of dynamo is based on principle of
  703. When the speed of a dc motor increases the armature current
  704. The coil of dynamo is rotating in a magnetic field. The developed induced e.m.f. changes and the number of magnetic lines of force also changes. Which of the following condition is correct
  705. Which of the following statement is incorrect
  706. Armature current in dc motor will be maximum when
  707. In an induction coil with resistance, the induced emf will be maximum when
  708. Work of electric motor is
  709. A device which converts electrical energy into mechanical energy is
  710. An electric motor operating on a 60 V dc supply draws a current of 10 A. If the efficiency of the motor is 50%, the resistance of its winding is
  711. In a region of uniform magnetic induction B=10 -2 tesla, a circular coil of radius 30 cm and resistance π 2 ohm is rotated about an axis which is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is
  712. An electron moves along the line AB, which lies in the same plane as a circular loop of conducting wires as shown in the diagram. What will be the direction of current induced if any, in the loop
  713. Two different coils have self-inductance L 1 = 8 mH, L 2 = 2 mH . The current in one coil is increased at a constant rate. The current in the second coil is also increased at the same rate. At a certain instant of time, the power given to the two coils is the same. At that time the current, the induced voltage and the energy stored in the first coil are i 1 ,   V 1 and W 1 respectively. Corresponding values for the second coil at the same instant are i 2 ,   V 2 and W 2 respectively. Then
  714. A physicist works in a laboratory where the magnetic field is 2 T. She wears a necklace enclosing area 0.01 m 2 in such a way that the plane of the necklace is normal to the field and is having a resistance R = 0.01 Ω . Because of power failure, the field decays to 1 T in time 10 –3 seconds. Then what is the total heat produced in her necklace ? (T = Tesla)
  715. Two identical coaxial circular loops carry current i each circulating in the clockwise direction. If the loops are approaching each other, then
  716. A conductor ABOCD moves along its bisector with a velocity of 1 m/s through a perpendicular magnetic field of 1 wb/m 2 , as shown in fig. If all the four sides are of 1m length each, then the induced emf between points A and D is
  717. A conducting rod PQ of length L = 1.0 m is moving with a uniform speed v = 2 m/s in a uniform magnetic field B = 4.0 T directed into the paper. A capacitor of capacity C = 10 μ F is connected as shown in figure. Then
  718. Shown in the figure is a circular loop of radius r and resistance R. A variable magnetic field of induction B = B 0 e − t is established inside the coil. If the key (K) is closed, the electrical power developed right after closing the switch is equal to
  719. Plane figures made of thin wires of resistance R = 50 milli ohm/metre are located in a uniform magnetic field perpendicular into the plane of the figures and which decrease at the rate dB/dt = 0.1 m T/s. Then currents in the inner and outer boundary are. (The inner radius a = 10 cm and outer radius b = 20 cm)
  720. A wire cd of length l and mass m is sliding without friction on conducting rails ax and by as shown. The vertical rails are connected to each other with a resistance R between a and b. A uniform magnetic field B is applied perpendicular to the plane abcd such that cd moves with a constant velocity of
  721. A conducting rod AC of length 4l is rotated about a point O in a uniform magnetic field B directed into the paper. AO = l and OC = 3l. Then
  722. How much length of a very thin wire is required to obtain a solenoid of length l 0 and inductance L
  723. What is the mutual inductance of a two-loop system as shown with centre separation l
  724. A coil having n turns and resistance R Ω is connected with a galvanometer of resistance 4 R Ω . This combination is moved in time t seconds from a magnetic field B 1 weber to B 2 weber. The induced current in the-circuit is
  725. A square loop of side 1 m is placed in a perpendicular magnetic field. Half of the area of the loop lies inside the magnetic field. A battery of e.m.l 10 V and negligible internal resistance is connected in the loop. [Fig. (3)]. The magnetic field changes with time according to the relation B = (0.01 – 2 t) tesla. The total e.m.f. of the battery will be
  726. A uniform horizontal magnetic field B exists in the region A B C D. A rectangular loop of mass m and horizontal side / and resistance R is placed in the magnetic field as shown in fig.(4). With what velocity should it be pushed down so that it continues to fall without acceleration ?
  727. A square loop of side 4 cm is lying on a horizontal table. A uniform magnetic field of 0.5 T is directed towards at an angle of 60 o to the vertical as shown in fig. If the field increases from zero to its final value in 0.2 s, the e.m.f. induced in the loop will be
  728. A straight conductor carrying current i and a loop closed by a sliding connector of resistance ,R lie in the same plane as shown in fig. (8). The connector slides towards right with a uniform velocity v. The induced current generated in the loop in terms of distance r of the connector from the straight conductor will be
  729. A square frame ABCD of side o and a long current carrying conductor PQ arc arranged as shown in fig.(7). If the frame moves towards right with a velocity ‘v’, the resultant induced e.m.f. in the loop will be
  730. Two loops with sides L and l (L>>l) are placed concentrically and coplanar as shown in fig. (9). The mutual inductance of the system is proportional to
  731. The length of each side of a square coil of 10 turns is 12 cm. This coil rotates in a magnetic field of flux density 0.025 tesla. If the maximum induced e.m.f. is 20 mV then angular velocity of the coil will be
  732. A rectangular coil of 20 turns and area of cross-section 25 sq. cm has a resistance of 100 Ω . If a magnetic field which is perpendicular to the plane of the coil changes at a rate of 1000 tesla per second, the current in the coil is
  733. The current in self-inductance L = 40 mH is to be increased uniformly from 1 amp to 11 amp in 4 milliseconds. The e.m.f. induced in inductor during process is
  734. Two coils are made of copper wires of same length. In the first coil the number of turns is 3 n and radius is r. In the second coil number of turns is n and the radius is 3r. The ratio of self-inductances of the coils will be
  735. An e.m.f. of 2 volt is produced in a coil when the current changes at a steady rate from 3 to 2 amperes in 1 milli-second. The value of self-inductance is
  736. Two pure inductors, each of self-inductance L are connected in parallel but are well separated from each other, then the total inductance is
  737. A long solenoid having 200 turns per cm caries a current of 1.5 amp. At the centre of it is placed a coil of 100 turns of cross-sectional area 3.14 x 10 -4 m 2 having its axis parallel to the field produced by the solenoid. When the direction of current in the solenoid is reversed within 0.05 sec., the induced e.m.f. in the coil is
  738. The inductance between A and D in fig.(11) is
  739. A circular coil of n t urns and radius r is placed in a uniform magnetic field B. Initially the plane of the coil is perpendicular to the field. The coil is rotated through 90 o . The resistance of the coil is ONE OHM. The quantity of charge passing through the coil is
  740. An ideal coil of 10 H is connected in series with a resistance of 5 Ω and a battery of 5V. 2 second after the connection is made, the current flowing in ampere in the circuit is
  741. A coil of 10 cm x 10 cm having 50 turns is making 50 r.p.s. in a mag1etic field of induction 2 tesla, The peak value of induced e.m.f. is approximately
  742. When the current changes from + 2 A to – 2 A in 0.05 second, an e.m.f. of 8 V is induced in a coil. The coefficient of self-induction of the coil is
  743. A galvanometer is connected to the secondary coil. The galvanometer shows an instantaneous maximum deflection of 7 divisions when current is started in the primary coil of the solenoid. Now if the primary coil is rotated though 180 o , then the new instantaneous maximum deflection will be
  744. A coil of area 100cm 2 having 50 turns is perpendicular to a magnetic field of intensity 0.02 weber/m 2 . The resistance of the coil is 2 Ω . If it is removed in 1 sec. from the magnetic field, the induced charge produced is
  745. A circular ring of diameter 20 cm has a resistance 0.01 ohm. How much charge will flow through the ring if it is rotated from position perpendicular to the uniform magnetic field of B = 2T to a position parallel to field
  746. The magnetic flux through a stationary loop with resistance R varies during interval of time ? as Φ = at ( T − t ) . The heat generated during this time neglecting the inductance of loop will be
  747. Switch S of the circuit shown in fig is closed at t = 0. If e denotes the induced e.m.f. in L and i, the current flowing through the circuit at time t, then which of the following graphs fig shows the variation of e with i
  748. Fig shows L-shaped rod rotating about its end O in a plane perpendicular to the magnetic field B. The part OA of the rod is non-conducting while the part AB is conducting. The induced e.m.f. between the ends A and B is
  749. Two circular coils can be arranged in any of the three situations shown in fig.. Their mutual inductance will be
  750. As shown in fig. (10), P and Q are two coaxial conducting loops separated by some distance. When the switch S is closed, a clockwise current I p flows in P (as seen by E) and an induced current I Q 1 , flows in Q. The switch remains closed for a long time. when S is opened, a current I Q 2 flows in Q. Then the directions of I Q 1 and I Q 2 (as seen by E) are:
  751. The magnetic flux ϕ through a coil varies with time t as shown in Fig. Which graph shown in Fig. best represents the variation of induced emf e in the coil with time t.
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