A solid object of mass M is made from a material of specific heat capacity C and specific latent heat of fusion L and of very high thermal conductivity enters the atmosphere from outer space, its temperature being below its melting point by !:!T. Because of atmospheric friction it absorbs energy at a constant rate R. The time before the solid becomes completely molten is given by:
A black body is at a temperature 300 K. It emits energy at a rate, which is proportional to:
A pan filled with hot food cools from 94 0 C to 86 0 C in 2 min. When the room temperature is at 20 0 C, the time taken to cool from 71 0 C to 69 0 C is
Two slabs A and B of different materials but of the same thickness are joined end- to-end to form a composite slab. The thermal conductivities of A and B are K 1 and K 2 , respectively. A steady temperature difference of 12 0 C is maintained across the composite slab. If K 1 = K 2 2 the temperature difference across slab A is
The rectangular surface of area 8cm x 4cmof a black body at a temperature of 127 0 C emits energy at the rate of E per second. If the length and breadth of the surface are each reduced to half of the initial value and the temperature is raised to 327 0 C, the rate of emission of energy will become:
A body cools from 60 0 C to 50 0 C in 10 min. If room temperature is 25 0 C. Temperature of body at the end of next 10 min, will be [UP CPMT 2012]
A piece of iron is heated in a flame It first becomes dull red then becomes reddish yelJow and finally turns to white hot. The correct explanation for the above observation is possible by using
An object kept in a large room having air temperature of 25°C takes 12 minutes to cool from 80°C to 70°C. The time taken to cool for the same object from 70°C to 60°C would be nearly,
On observing light from three different stars P, Q and R. It was found that intensity of violet colour is maximum in the spectrum of P, the intensity of green colour is maximum in the spectrum of R and the intensity of red colour is maximum in the spectrum of Q. If T p , T Q and T R are the respective absolute temperature of P, Q and R, then it can be concluded from the above observations that
A body which is initially at 80 0 C cools to 64 0 C in 5 min and to 52 0 C in 10 min . The temperature of the surrounding should be
A black body is heated from 27 0 C to 127 0 C . The ratio of their energies of radiation emitted will be
A spherical black body with a radius of 12 cm radiates 440 W power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be
Certain quantity of water cools from 70 0 C to 60 0 C in the first 5 minutes and to 54 0 C in the next 5 minutes. The temperature of the surroundings is
What is the approximate surface temperature of a Yellow star? Wiens’s constant = 0.288 cmK
Two ends of rods of length L and radius r of the same material are kept at the same temperature. Which of the following rods conducts most heat ?
Which of the following circular rods (given : radius rand length l) each made of the same material and whose ends are maintained at the same temperature will conduct most heat ?
A slab of ice is one half covered with black cloth and the other half with white cloth. This is then placed in sunlight. After some time the pieces of cloth are removed. Which of the following statements is correct ?
A spherical black body with a radius of 12 cm radiates 450 W power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be:
If the temperature of the sun is doubled, the rate of energy received on earth will be increased by a factor of:
A black body radiates 20 W temperature 227°C. If temperature of the black body is changed to 727°C then its radiating power will be:
Assuming the sun to be a spherical body of radius R at a temperature of T K, evaluate the total radiant power, incident on earth, at a distance r from the sun: Radius of earth is r 0 .
If the radius of a star is R and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is Q ?
A sphere and a cube of same material and same total surface area are placed in the same evacuated space turn by turn after they are heated to the same temperature. Find the ratio of their initial rates of cooling in the enclosure.
The total radiant energy per unit area, normal to the direction of incidence, received at a distance R from the centre of a star of radius r, whose outer surface radiates as a black body at a temperature T K is given by :
If temperature of a black body increases from -73°C to 327°C, then ratio of emissive power at these two temperatures is:
Four spheres P, Q, R and ,S are of same radius but made of different metals. Their densities are in the ratio 3 : 4 :6 : 5 and specific heats are in the ratio 2 : 5 : 3 : 6. These are initially kept at same temperature and placed in the same surroundings. The sphere which has the slowest rate of cooling is:
A sphere maintained at temperature 600 K, has cooling rate R in an external environment of 200 K temperature. If its temperature falls to 400 K, the cooling rate will be:
A body in a room cools from 90 o C to 80 o C in 5 minute. The time taken to cool from 70 o C to 60 o C is ?
A sphere and cube made of same material and having same surface area are heated to the same temperature and kept in the same surroundings. The ratio of their initial rates of cooling will be:
Three objects coloured black, gray and white can withstand hostile conditions up to 2800°C. These objects are thrown into a furnace where each of them attains a temperature of 2000°C. Which object will glow brightest ?
The Wien’s displacement law express relation between:
The graphs shown in the figure represent energy density E λ versus λ for three A sources sun, welding arc and tungsten filament. For λ max , correct combination will be :
Which of the following curves represents spectral distribution of energy of black body radiation?
Consider the following statements. (A) It is hotter over the top of a fire than at the same distance on the sides. (B) Air surrounding the fire conducts more heat upwards. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Infrared radiation is detected by:
Consider the following statements. (A) All black coloured objects are considered black bodies. (B) Black colour is a good reflector of heat. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Perspiration from human body helps in cooling the body. (B) A thin layer of water on the skin enhances its emissivity. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Blue star is at high temperature than red star. (B) According to Wien’s displacement law λ m = b T , where symbols have their usual meanings. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Two spheres of same material have radii r 1 and r 2 respectively and temperatures 4000 K and 2000 K respectively. The energy radiated per second by first sphere is more than second sphere. (B) In thermal conduction, energy is transferred by transference of particles of conducting body. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
The emission spectrum of a black body at two different temperatures are shown by curyes P and Q (as shown in figure). The ratio of the areas under the two curves P and Q will be
Consider the following statements. (A) A body that is a good radiator is also a good absorber of radiation at a given wavelength. (B) According to Kirchhoff’s law the absorptivity of a body is equal to its emissivity at a given wavelength. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Woolen cloth keep the body warm in winter. (B) Air is a bad conductor of heat. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Conduction usually takes place in solids, convection in liquids and gases and no medium is required for radiation. (B) In conduction and convection, heat is transferred from one place to other by actual motion of heated material. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
A slab of stone of area 0.36 m 2 and thickness 0.1 m is exposed on the lower surface to steam at 100°C. A block of ice at 0°C rests on the upper surface of the slab. In 56 minutes 4.8 kg of ice is melted. The thermal conductivity of slab is: (Given latent heat of fusion of ice= 3.36 x 10 5 J kg -1 )
A black body has maximum wavelength λ m at 2000 K. Its corresponding wavelength at 3000 K will be
In a composite rod, when two rods of different lengths and of the same area of cross-section are joined end to end, then if K is the effective coefficient of thermal conductivity I 1 + I 2 k is equal to
Same quantity of ice is filled in each of the two metal containers P and Q having the same size, shape and wall thickness but made of different materials. The containers are kept in identical surroundings. The ice in P melts completely in time t 1 , whereas in Q takes a time t 2 . The ratio of thermal conductivities of the materials of P and Q is
The black body spectrum of an object O 1 is such that its radiant intensity (i.e. intensity per unit wavelength interval) is maximum at a wavelength of 200 nm. Another object O 2 has the maximum radiant intensity at 600nm. The ratio of power emitted per unit area by source O 1 to that of source O 2 is
The temperature at the two ends A and B of a rod of length 25 cm and circular cross-section are 100 0 C and 0 0 C, respectively. In the steady state, the temperature at a point 10 cm from the end B is (Ignore loss of heat from curved surface of the rod)
The unit of thermal conductivity is
A black body radiates power P and maximum energy is radiated by it around a wavelength λ 0 . The temperature of the black body is now changed such that it radiates maximum energy around the wavelength 3 λ 0 4 The power radiated by it now is :
A room at 20 0 C C is heated by a heater of resistance 20 ohms connected to 200 V mains. The temperature is uniform throughout the room and heat is transmitted through a glass window of area 1 m 2 and thickness 0.2 cm. Calculate the temperature outside [K for glass is 0.2 cal/ m / 0 C and J = 4.2 J/cal]
Two rods with the same dimensions have thermal conductivities in the ratio 1:2. They are arranged between heat reservoirs with the same temperature difference, in two different configurations A and B. The rates of heat flow in A and B are I A and I B respectively. The ratio I A I B is equal to
Four identical pieces of copper are painted with different types of paints. Which one would you expect to lose heat most rapidly if they are all heated to the same temperature and allowed to coal in vaccum
When temperature of air goes below the freezing point of water a layer of ice is formed on the surface of water in a lake. If at time t thickness of ice layer is x, Then which of the following graphs correctly shows the variation of x with time t?
Two spherical bodies A and B of diameter d = 0.0344 m m are heated to the same temperature and allowed to coal in the same ambient temperature. Ratio of emissivities of their surfaces is 1 : 2, ratio of their specific heats is 2 : 3, ratio of their radii is 2 : 1 and ratio of their densities is 1 : 3. Then ratio of their initial rate of cooling is
Ratio of radii of two cylinders is 1 : 2 and that of their lengths is 2 : 3. The cylinders are heated to the same temperature and allowed to cool in the same surrounding. Then the ratio of their initial rate of cooling is
A black body radiates maximum energy at wavelength λ when its temperature is T. Now temperate of the black body is increased by 50%. Then the percentage change in wavelength at which the black body will radiate maximum energy is
A spherical object cools from 80 0 C t o 64 0 C i n 5 min . The same body cools from 80 0 C t o 52 0 C i n 10 min . Then temperature of the surrounding is
Temperature of a body ( θ ) is slightly more than the temperature of the surrounding ( θ 0 ) . Its rate of cooling (R) versus temperature of body ( θ ) is plotted. Its shape would be
For water at 0ºC it takes one hour for first 3 mm of ice layer formation. How much time will it take for next 6 mm of ice formation?
Which of the following combination of properties would be most desirable for a cooking pot :
If the distance between a point source & absorber is halved then Intensity of radiant energy will be
A Block of Ice
Of the following the fastest process of heat transfer is
A) A hot hollow sphere in vacuum cools by convection B) A hot solid sphere in vacuum cools by radiation
Variation of radiant energy emitted by sun, filament of tungsten lamp and welding arc as a function of its wavelength is shown in figure. Which of the following option is the correct match ?
A) A body of low Thermal capacity gets heated or cooled quickly B) Good emitters are bad reflectors
S.I. Unit of temperature gradient is
The unit of thermal conductivity is
If the radius of a star is R and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is Q?
A body cools from a temperature 3T to a temperature 2T in 10 minutes. The room temperature is T. Assume that Newton’s law of cooling is applicable. The temperature of the body at the end of next 10 minutes will be
A body is heated to 327 o C and then allowed to cool in air which is at 27 o C . Initial rate of cooling of the body is R. What will be the rate of cooling of the body when its temperature falls to 227 o C ?
Heat is flowing through two cylindrical rods of the same material. The diameters of the rods are in the ratio 1 : 2 and their lengths are in the ratio 2 : 1. If the temperature difference between their ends is the same, then the ratio of the amounts of heat conducted through them per unit time will be:
Two conducting slabs having same shape and size of heat conductivities k 1 and k 2 joined as shown in figure. The temperature at ends of the slabs are θ 1 and θ 2 ( θ 1 > θ 2 ). The final temperature of junction ( θ m ) is:
Two identical rods AC and CB made of two different metals having thermal conductivities in the ratio 2 : 3 are kept in contact with each other at the end C.as shown in the Fig. A is at 100°C and B is at 25°C. Then the junction C is at :
Two rods of same length and areas of cross-section A 1 and A 2 have their ends maintained at same temperature. If K 1 and K 2 are their thermal conductivities, C 1 and C 2 are the specific heats of their material and ρ 1 , ρ 2 their densities, then for the rate of flow by conduction through them to be equal:
Which of the following statements is wrong ?
In natural convection, a heated portion of a liquid moves because:
A black body at a high temperature T K radiates energy at the rate E watt /m 2 ; when the temperature falls to (T/2) K the radiated energy will be:
The unit of Stefan’s constt. is:
A black body is heated from27° to 127°C. The ratio of their energies of radiation emitted will be
A sphere, a cube and a thin circular plate all made of the same mass and finish are heated to a temperature of 200 o C; which of these objects will cool slowest when left in air at room temperature ?
According to Newton’s law of cooling, the rate of cooling of a body is proportional to (A0)”, where A0 is the difference of the temperature of the body and the surroundings, and n is equal to:
A solid sphere and a hollow sphere of same material and size are heated to same temperature and allowed to cool in the same surroundings. If the temperature difference between each sphere and its surroundings is T, then:
A sphere, a cube and a thin circular plate, all of same material and same mass are initially heated i.e.,same high temperature; then:
A black body is at 727°C. It emits energy at a rate which is proportional to :
A black body at 227°C radiate heat at the rate of 7 cal/cm 2 s. At a temperature 727°C, the rate of heat radiated in the same unit will be :
In a room where the temperature is 30 o C a body cools from 61 o C to 59 o C in 4 minute. The time taken by the body to cool from 51 o C to 49 o C will be:
Shown below are the black body radiation curves at temperatures T 1 and T 2 ( T 2 > T 1 ) . Which of the following plots is correct?
body cools from 50°C to 49°C in 5 s. How long will it take to cool from 40°C to 39°C? Assume temperature of surroundings to be 30°C and Newton’s law of cooling is valid:
The intensity of radiation emitted by the Sun has its maximum value at a wavelength of 510 nm and that emitted by the North Star has the maximum value at 350 nm. If these stars behave like black bodies, then the ratio of the surface temperatures of the Sun and the North Star is:
If a solid sphere and a hollow sphere of the same material and radius are heated to the same temperature: (i) both will emit equal amount of radiation per sec in the beginning (ii) both will absorb equal amount of radiation per sec in the beginning (iii) the initial rate of cooling will be same for both the spheres (iv) the two spheres will have same temperature at any instant
A body cool from 90°C to 70°C in 10 minutes if temperature of surrounding is 20°C find the time taken by body to cool from 60 °C to 30 °C. Assuming Newton’s law of cooling is valid:
We consider the radiation emitted by the human body. Which of the following statements is true ?
Three discs A, B and C having radii 2 m, 4 m and 6 m respectively are coated with carbon black on their outer surfaces. – The wavelengths corresponding to maximum intensity are 300 nm, 400 nm and 500 nm respectively. The power radiated by them are Q A , Q B and Q C respectively:
Consider the following statements. (A) The colour of a star is an indication of its size. (B) Rate of cooling is proportional to temperature difference between body and its surrounding. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Two thin blankets put together are warmer than a single blanket of double the thickness. (B) Thickness of blanket increases because of air layer enclosed between the two blankets. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Variation of radiant energv emitted by sun. filament of tungsten lamp and welding arc as a function of its wavelength is shown in figure. Which of the following option is the correct match?
Consider the following statements. (A) Bodies radiate heat at all temperatures. (B) Rate of radiation of heat is proportional to the fourth power of absolute temperature.
Two circular discs A and ,B with equal radii are blackened. They are heated to same temperature and are cooled under identical conditions. What inference do your draw from their cooling curves?
Consider the following statements. (A) Coolness is felt in summer when we enter in an air conditioned room. (B) At every possible temperature there is a continuous heat energy exchange between a body and its surrounding. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) A good absorber is a good emitter. (B) For a substance, absorbtance is equal to emissivity. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Two stars A and B radiate maximum energy at 360 nm and 4800 A respectively. Ratio of their absolute temperature is 4:3. (B) According to Wien’s displacement law λ m T = b , where symbols have their usual meaning. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) A hot body is kept in some surrounding. As it cools, its temperature falls from 80°C to 78°C in a time duration t 1 and from 50°C to 48°C in time duration t 2 . The temperature of surrounding is constantly 20°C, then t 1 > t 2 . (B) According to Newton’s law of cooling; rate of cooling depends only on the difference of temperatures of the body and the surrounding. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at wavelength 250 nm is U 1 , at wavelength 500 nm is U 2 and that at 1000 nm is U 3 . Wien’s constant, b = 2.88 x 10 6 nmK. Which of the following is correct?
A cylindrical rod having temperatures T 1 and T 2 at its ends. The rate of flow of heat is Q 1 cal/sec. If all the dimensions are doubled keeping T 1 and T 2 constant, then rate of flow of heat Q 2 will be:
Two rods are of same material and have same length and area. Heat ∆ Q flows through them in 12 minutes, when they are joined side by side. If now both the rods are joined in parallel, then the same amount of heat ∆ Q will flow in:
Water can be heated in a cup of paper because:
Two identical plates of metal are welded end to end as shown in Fig. (A) 20 cal of heat flows through it in 4 minute. If the plates are welded as shown in Fig. (B) the same amount of heat will flow through the plates in.
A black body at a temperature of 1640 K has the wavelength corresponding to maximum emission equal to 1.75 μ. Assuming the moon to be a perfectly black body, the temperature of the moon, if the wavelength corresponding to maximum emission is 14.35 μ is:
The power radiated by a black body is P and it radiates maximum energy around the wavelength λ o – Now the temperature of the black body is changed so that it radiates maximum energy around wavelength λ 0 / 2 . The power radiated by it will now increase by a factor of:
A sphere of density p, specific heat capacity c and radius r is hung by a thermally insulating thread in an enclosure which is kept at a lower temperature than the sphere. The temperature of the sphere starts to drop at a rate which depends upon the temperature difference between the sphere and the enclosure and the nature of the surface of sphere and is proportional to:
One end of a copper rod of length 1 .0 m and area of cross-section 10 -3 m 2 is immersed in boiling water and the other end in ice. If the coefficient of thermal conductivity of copper is 92 cal/m/s/°C and the latent heat of ice is 8 x 10 4 cal /kg, then the amount of ice which will melt in one minute is
The ends of two rods of different materials having thermal conductivities, radii of cross-section and Iengths in the ratio 1 : 2, arc maintained at the same temperature difference. If the rate of flow of heat in the larger rod is 4 cal/s, then in shorter rod in cal/s will be
Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in 20 minutes and 35 minutes respectively. The ratio of thermal conductivities of the metal is
A solid copper sphere (density p and specific heat c) of radius .r at an initial temperature 200 K is suspended inside a chamber whose walls are at almost O K. The time required for the temperature of the sphere to drop to 100 K is
A cylinder of radius R made of a material of thermal conductivity & is surrounded by a cylindrical shell of inner radius .E and outer radius 2 .R made of a material of thermal conductivity K 2 . The two ends of the combined system are maintained at two different temperatures. There is no loss of heat across the cylindrical surface and the systems in steady state. The effective thermal conductivity of the system is
Two slabs A and B of different materials but of the same thickness are joined as shown in fig. (2). The thermal conductivities of A and B are K 1 and K 2 respectively. The thermal conductivity of the composite slab is
The light from the sun is found to have a maximum intensity near 470 nm. Assuming the surface of the sun behaves as a black body. the temperature of sun will be
The graph shown in fig. represents energy density E λ versus λ for three sources : sun, welding arc and tungsten filament. For λ max , correct combination will be
The earth receives at its surface radiation from the sun at the rate of 1400 W/m2. The distance of the centre of the sun from the surface of the earth is 1.5 x 10 11 m and the radius of the sun is 7.0 x 10 8 m. Treating the sun as a black body it follows from the above data that its surface temperature is
Two spheres P and Q, of same colour having radii B cm and 2 cm are maintained at temperature 127°C and 527°C respectively. The ratio of energy radiated by P and Q is
Which of the following curves . is a cooling curve ?
Two metallic spheres S 1 and S 2 are made of the same material and have got identical surface finish. The mass of S 1 is thrice that of S 2 . Both the spheres are heated to the same high temperature and placed in the same room having lower temperature but are thermally insulated from each other. The ratio of initial rate of cooling of S 1 to that of S 2 is
A hot liquid takes 5 minutes to cool from 70°C to 60°C. How long will it take to cool from 60°C to 50°C ?
The maximum energy in the thermal radiation from a hot source occurs at a wavelength of 11 x 10 -5 cm. According to Wien’s law, the temperature of the source (on Kelvin scale) will be n times the temperature of another source (on Kelvin’s scale) for which the wavelength at maximum energy is 5.5 x 10 -5 cm. The value of n is
A body cools from 50.0°C to 49.9°C in 5 s. How long will it take to cool from 40.0°C to 39.9°C ? Assume the temperature of surroundings to be 30.0°C and Newton’s law of cooling to be valid
One end of a thermally insulated rod is kept at a temperature T 1 and the other at T 2 . The rod is composed of two sections of lengths l 1 and l 2 and thermal conductivities k 1 and k 2 respectively. The temperature at the interface of the two sections is
For most practical temperature we may take it that all bodies radiate heat in proportion to the fourth power of temperature T. If a body (coated black) at 400 K surrounded by atmosphere at 300 Khas cooling rate r 0 , the same body at 900 K, surrounded by the same atmosphere, will have cooling rate closer to
The maximum energy in the thermal radiation hot a hot source occurs at a wavelength of 11×10 -5 cm. According to Wien’s law, the temperature of the source (on Kelvin scale) will be n times the temperature of another source (on Kelvin scale) for which the wavelength at maximum energy is 5.5 x 10 -5 cm. The value on of n is
A black body is at a temperature of 2880 K. The energy of radiation emitted by this body with wavelength 499 nm and 500 nm is U 1 , between 999 nm and 1000 nm is U 2 and between 1499 nm and 1500 nm is U 3 . The Wien’s constant b = 2.88 x 10 6 nm K. Then
A spherical black body with a radius of 12 cm radiates 450 W power of 500 K. If the radius were half and temperature doubled, the power radiated in watt would be
A sphere, a cube and a thin circular plate are heated to the same temperature. If they are made of same material and have equal masses then which one of the three objects cools faster
The earth radiates in the infra-red region of the spectrum. The spectrum is correctly given by
A black body is at a temperature of 2800 K. The energy of radiation emitted by this object with wavelength between 499 nm and 500 nm is U 1 and between 999 nm and 1000 nm is U 2 . The Wien constant, b = 2.80 x 10 6 nmK. Then
A liquid cools from 50°C to 45°C in 5 minutes and from 45 to 41.5°C in the next 5 minutes. The temperature of the surrounding is
The maximum energy in the thermal radiation hot a hot source occurs at a wavelength of 11 x 10 -5 cm. According to Wien s law, the temperature of the source [on Kelvin scale) will be n times the temperature of another source (on Kelvin’s scale) for which the wavelength at maximum energy is 5.5 x 10 -5 cm. The value of n is
Two identical conducting rods AB and CD are connected to a circular conducting ring at two diametrically opposite points B and C . The radius of the ring is equal to the length of rods AB and CD . The area of cross-section, thermal conductivity of the rod and ring are equal. Points A and D are maintained at temperatures of 100 0 C and 0 0 C. Temperature at point C will be
Consider the following statements. (A) Water cannot be boiled inside a satellite by convection. (B) In weightlessness conditions, natural movement of heated fluid is not possible.
The surface temperature of the sun which has maximum energy emission at 500 nm is 6000 K. The temperature of a star which has maximum energy emission at 400 nm will be:
Two spheres of the same material have radii 1 m and 4 m and temperatures 4000 K and 2000 K respectively. The energy radiated per second by the first sphere is
A metal piece is heated up to T K; the temperature of the surrounding is t K. The heat loss to the surrounding due to radiation is proportional to:
Consider the following statements. (A) For higher temperature, the peak emission wavelength of a black body shifts to lower wavelengths. (B) Peak emission wavelength of a black body is proportional to the forth power of its absolute temperature.
Three rods made of the same material and having the same cross-section have been joined as shown in the figure. Each rod is of the same length. The left and right ends are kept at 0°C and 90°C respectively. The temperature of the junction of the three rods will be
A cylinder of radius R made of a material of thermal conductivity K 1 is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a material of thermal conductivity K 2 . The two ends of the combined system are maintained at two different temperatures. There is no loss of heat across the cylindrical surface and the system is in steady state. The effective thermal conductivity of the system is
Two plates of same area are placed in contact. Their thickness as well as thermal conductivities are in the ratio 2:3. The outer surface of one plate is maintained at 10°C and that of the other at 0 DC. What is the temperature at the common surface?
In a room, where the temperature is 30 0 C, a body cools from 61 0 C to 59 0 C in 4 min. The time taken by the body to cool from 51 0 C to 49 0 C will be [MP PMT 2013)
If the radius of a star is R and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is Q ?
For maximum radiant energy from the moon, the corresponding wavelength is 14 micron. If Wien’s constant is b = 2892 X 10 – 6 mK, then temperature of the moon is
Two stars A and B radiate maximum energy at the wavelength of 360 nm and 480 nm, respectively. Then, the ratio of the surface temperatures of A and B is
The two ends of a metal rod are maintained at temperatures 100 0 C and 110 0 C. The rate of heat flow in the rod is found to be 4 Js − 1 . If the ends are maintained at temperatures 200 0 C and 210 0 C, the rate of heat flow will be
Two identical black bodies are maintained at 500 K and 1000 K respectively. The ratio of their maximum spectral emission densities is
The coefficient of thermal conductivity of copper is 9 times that of steel. In the composite cylindrical bar shown in the figure. What will be the temperature at the junction of the copper and steel.
In solar radiation, the intensity of radiation is maximum around the wavelength λ . If R is the radius of the sun and c is the velocity of light, the mass lost by the sun per second is proportional to
The adjoining diagram shows the spectral energy density distribution E λ of a black body at two different temperatures. If the areas under the curves are in the ratio 256 : 1, the value of temperature T is
The power radiated by a black body is P and it radiates maximum energy at wavelength, λ 0 . If the temperature of the black body is now changed so that it radiates maximum energy at wavelength 3 4 λ 0 the power radiated by it becomes nP . The value of n is
Certain quantity of water cools from 70°C to 60°C in the first 5 minutes and to 54°C in the next 5 minutes. The temperature of the surroundings is
A black body is at a temperature of 5760 K . The energy of radiation emitted by the body at wavelength 250 n m is U 1 , at wavelength 500 n m is U 2 and that at 1000 n m is U 3 . Wien’s constant, b = 2 . 88 × 10 6 n m K . Which of the following is correct?
Rate of cooling dθ dt of a body depends upon
Two bulbs have filaments of lengths, Emissivities and diameters in the ratio of 2 :1. If ratio of their powers is 1 : 2 then, ratio of their temperature is
An ideal black body at room temperature is thrown into a furnace. It is observed that
The two ends of a metal rod are maintained at temperatures 100°C and 110° C. The rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures 200°C and 210°C, the rate of heat flow will be
A body cools from a temperature 3T to 2T in 10 minutes. The room temperature is T. Assume that Newton’s law of cooling is applicable. The temperature of the body at the end of next 10 minutes will be
On observing light from three different stars P, Q and R, it was found that intensity of violet colour is maximum in the spectrum of P, the intensity of green colour is maximum in the spectrum of R and the intensity of red colour is maximum in the spectrum of Q. If T P , T Q and T R are the respective absolute temperatures of P, Q and R, then it can be concluded from the above observations that
Two metal rods 1 and 2 of same lengths have same temperature difference between their ends. Their thermal conductivities are K 1 a n d K 2 and cross sectional areas A 1 a n d A 2 , respectively. If the rate of heat conduction in 1 is four times that in 2 , then
The opposite faces of a cubical block of iron of cross section 4 square cm are kept in contact with steam and melting ice. Calculate the quantity of ice melted at the end of 10 minutes, k for iron = 0.2 cgs units.
Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K 1 a n d K 2 . The thermal conductivity of the composite rod will be
A spherical black body with a radius of 12cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be
Three stars A, B, C have surface temperatures T A , T B , T C respectively. Star A appears bluish, star B appears reddish and star C yellowish. Hence,
A and B are two points on a uniform metal ring whose centre is C. The angle A C B = θ . A and B are maintained at two different constant temperatures. When θ = 180 0 , the rate of total heat flow from A to B is 1.2 W. When θ = 90 0 , this rate will be
Two circular discs A and B with equal radii and mass are blackened. They are heated to same temperature and are cooled under identical conditions. What inference can be drawn from their cooling curves?
In a certain planetary system, it is observed that one of the celestial bodies having a surface temperature of 200 K, emits radiation of maximum intensity near the wavelength 12 μ m . The surface temperature of a nearby star which emits light of maximum intensity at a wavelength λ = 4800 A o ,is :
A wall consists of alternating blocks of length ‘d’ and coefficient of thermal conductivity k 1 a n d k 2 respectively as shown in figure. The cross sectional area of the blocks are the same. The equivalent coefficient of thermal conductivity of the wall between left and right is :
The plots of spectral radiancy R λ versus wave length λ for three black bodies at temperatures T 1 , T 2 a n d T 3 respectively are shown. Their temperatures are such that
A metallic sphere having inner and outer radii ‘a’ and ‘b’ respectively has thermal conductivity K = K 0 / r 2 a ≤ r ≤ b where K 0 is a constant. The thermal resistance between inner and outer surface is
A surface at temperature T 0 Kelvin receives power P by radiation from a small sphere at temperature T > > T 0 and at a distance d. If both T and d are doubled, the power received by the surface will become approximately
A composite rod ABC is made of two rods AB and BC of same cross-sectional area. Material of AB has coefficient of thermal conductivity K and that of rod BC is k 2 . In steady state , temperature of junction B is
Two metallic spheres P and Q are of same surface finish and same density. Weight of P is twice that of Q. Both spheres are heated to same temperature and are left in room to cool by radiation. The ratio of initial rate of cooling of P to that of Q is
If a liquid is heated in weightlessness. The heat is transmitted through
Power radiated by a black body is P 0 and the wavelength corresponding to maximum energy is around λ 0 . On changing the temperature of the black body, it was observed that the power radiated becomes 256 81 P 0 . The shift in wavelength corresponding to the maximum energy will be
A steam chamber is connected to an ice block at 0 0 C , by means of two two identical rod in series . It is observed that 100 gm of ice is melted in 10 minutes. If they are connected in parallel amount ice melt in 5 minutes in gm is
The maximum energy in thermal radiations from a blackbody occurs at wavelength 4000 Å. The effective temperature of the source is :
A spherical body of area A and emissivity e = 0.6 is kept inside a perfectly black body. Energy radiated per second by the body at temperature T is
Two rods 1 and 2 have cross sectional areas A and 2A. Ratio of their length is 1 : 2, ratio of their coefficient of thermal conductivities is 4 : x. When the ends of the rods are maintained at temperatures θ 1 o C and θ 2 o C ( θ 1 > θ 2 ) , they conduct heat at the same rate. Then the value of x is
1 cm thick layer of ice is formed on a lake. Temperature of air is − 10 0 C . Coefficient of heat conduction of ice is 4 × 10 − 4 k c a l m − 1 s − 1 , density of ice = 9 × 10 3 k g / m 3 and Latent heat of ice = 80 k cal / kg. Then the rate of conduction of heat through unit area of ice layer is
What is the approximate surface temperature of red star?
Two rods AB and BC of same cross sectional area but of length l and 2 l are joined end to end as shown in figure. The coefficients of thermal conductivity of the rods are 2K and 3K respectively. Then in steady state temperature of junction B is
Which of the following cylindrical rods will conduct most heat when their ends are maintained at steady temperatures θ 1 o C and θ 2 o C ? The rods are made of same material.
Intensity of the radiation from the surface of a black body is maximum at a wavelength of 5760 A 0 . If Wien’s constant is 0.288 kelvin-cm. Then the power radiated per unit area of the surface of a black body is
Two spheres, one solid and another hollow are made up of same material and are of some radius. Both the spheres are heated to same temperature To. Now both spheres are left to cool in an atmosphere having temperature T A T A < < T 0 After time t, the temperature of solid sphere becomes T 1 and that of hollow sphere becomes T 2 . Then
A rod of length 1 m having cross-sectional area 0.75 m 2 conducts heat at 6000 Js –1 . Then the temperature difference acorss the rod is, if K = 200 Wm –1 K –1
In steady state condition, the temperatures at the two ends of a metal rod of length 25 cm are 100°C and 0°C. Then temperature at a point 8cm from the hot end is
The ratio of radii of two cylindrical rods of same material is 2 :1 and ratio of their lengths is 2 : 3. Their ends are maintained at same temperature difference. If rate of flow of heat in the longer rod is 2 Cal s -1 , then that in the shorter rod will be
One end of a cylindrical rod is kept in steam chamber and the other end in melting Ice. Now 0.5 gm of ice melts in 1 sec. If the rod is replaced by another rod of same length, half the diameter and double the conductivity of the first rod, then rate of melting of ice will be
Two vessels made of different materials are identical in all respects. The same quantity of Ice filled in them gets melted in 27 min. and 45 min. when placed in same surroundings. If thermal conductivity of material of 1st vessel is 180 wm -1 k -1 , then Thermal conductivity of material of second vessel will be
Equal temperature difference exists between the ends of two metallic rods 1 and 2 of equal length. Their thermal conductivities are K 1 and K 2 and cross sectional areas are resepctively A 1 and A 2 . The condition for equal rate of heat transfer will be
If reflecting and transmitting powers of a body are 0.2 and 0.3 units, then its Absorptive power will be
The rate of emission of radiation of a black body at temperature 27 o C is E 1 . If its temperature is increased to 327 o C the rate of emission of radiation is E 2 . The relation between E 1 and E 2 is
The radiation emitted by a star "A" per second is 10,000 times that of the sun. If the surface temperatures of the sun and the star A are 6000K and 2000K respectively, the ratio of the radii of the star A and the sun is
The wavelength of maximum emitted energy of a body at 700K is 4.08µm. If the temper-ature of the body is raised to 1400 K, the wavelength of maximum emitted energy will be
The rectangular surface of area 8cm × 4cm of a black body at a temperature of 127 0 C emits energy at rate of E per second. If the length and breadth are reduced to half of its initial value and the temperature is raised to 327 0 C, the rate of emission of energy will be
Two objects A and B have same shape and area. The Emissivity of A is 0.2 and that of B is 0.8. Each radiates same power. The ratio of their absolute temperatures is
If the maximum intensity of radiation for a black body is found at 2.65µm, the tempera-ture of the surface of radiating body is (Wien’s constant = 2.9×10 –3 mK)
A Black metal foil receives radiation of power P from a hot sphere at absolute temperature T, kept at a distance d. If the temperature is doubled and distance is halved, then Power will be
A body cools from 70 0 C to 50 0 C in 5 minutes. Temperature of surroundings is 20 0 C. Its temperature after next 10 minutes is
Certain quantity of water cools from 70 0 C to 60 0 C in the first 5 minutes and to 54 0 C in the next 5 minutes. The temperature of the surroundings is
If wavelengths of maximum intensity of radiations emitted by the sun and the moon are 0.5 ×10 –6 m and 10 –4 m respectively, the ratio of their temperatures is
A body at 50 0 C cools in a surroundings maintained at 30 0 C. The temperature at which the rate of cooling is half that of the begining is
A hot body is placed in cooler surroundings. When the body temperature is 75°C, the rate of cooling is 4°C/ min. When it is 55°C, the rate of cooling is 2°C/ min. The temperature of the surroundings is
The wavelength of maximum energy released during an atomic explosion was 2.93 × 10 –10 m. Given that Wein’s constant is 2.9×10 –3 m–K, the maximum temperature attained must be of the order of
A deep rectangular pond of surface area A,containing water (density = ρ, specific heat capacity=s), is located in a region where the outside air temperature is at a steady value of –26°C. The thickness of the frozen ice layer in this pond, at a certain instant is x. Taking the thermal conductivity of ice as K, and its specific latent heat of fusion as L, the rate of increase of the thickness of ice layer, at this instant would be given by :
Two rods A and B of same length and radius are joined together end to end. The thermal conductivity of A and B are 2K and K. Under steady state conditions, if temperature difference between the open ends of A and B is 36 0 C, the temperature difference across 'A' is
It is hotter over top of the fire than at same distance on the sides due to
Thermal radiation falls in
A cup of hot tea on a metal table in a room loses heat by
In summer, a mild wind is often found on the shore of a calm river. This is accused due to
In which of the following process, convection does not take place primarily ?
A) Natural convection can take place in gravity free region B) Forced convection is the principle in maintaining constant temperature of our body.
A body is allowed to cool in still air. Its temperature falls from 70 o C to 64 o C in 5 minutes and then from 64 o C to 60 o in another 5 minutes. Assuming Newton’s Law of cooling is valid, find the temperature of air.
When a spherical black body of radius r, having surface temperature 127 o C is allowed to cool in still air at 27 o C , its initial rate of cooling is ‘R’. What will be the initial rate of cooling of a black body having surface temperature 227 o C and radius 2r when allowed to cool in the same environment?
Fraunhofer line of the solar system is an example of
The colour of a star indicates its
An ideal black body at room temperature is thrown into a furnace. It is observed that
Assertion : If the temperature of a star is doubled then the rate of loss of heat from it becomes 16 times. Reason : Specific heat varies with temperature.
Assertion: Water kept in an open vessel will quickly evaporate on the surface of the moon. Reason: The temperature at the surface of the moon is much higher than boiling point of the water.
According to Newton’s law of cooling, the rate of cooling of a body is proportional to ( ∆ θ ) n , where ∆ θ is the difference of the temperature of the body and the surroundings, and n is equal to
Statement I : Coefficient of absorption of radiation of an ideal black body is 1. Statement II : An ideal black body emits radiation of all wavelength
Statement I : According to Newton’s law of cooling, the rate of loss of heat, – dQ dt of the body is directly proportional to the difference of temperature. Statement II : This law holds for all type of temperature differences.
A black body is at a temperature 300 K. It emits energy at a rate, which is proportional to
Two metallic spheres S 1 and S 2 are made of the same material and have identical surface finish. The mass of S 1 is three times that of S 2 . Both the spheres are heated to the same high temperature and placed in the same room having lower temperature but are thermally insulated from each other. The ratio of the initial rate of cooling of S 1 to that of S 2 is
A sphere, a cube and a thin circular plate, all made of the same material and having the same mass are initially heated to a temperature of 1000 0 C. Which one of these will cool first?
If the temperature of the sun were to be increased from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on the earth to what it was previously will be
The coefficients of thermal conductivity of copper, mercury and glass are respectively K c , K m and K g such that K c > K m > K g . If the same quantity of heat is to flow per second per unit area of each and corresponding temperature gradients are X c , X m and X g , then
The power radiated by a black body is P and it radiates maximum energy at wavelength, λ 0 . If the temperature of the black body is now changed so that it radiates maximum energy at wavelength 3 4 λ 0 , the power radiated by it becomes nP. The value of n is
If the temperature of the sun(black body) is doubled, the rate of energy received on earth will be increased by a factor of
Which of the following is the example of ideal black body?
Newton’s law of cooling is used in laboratory for the determination of the
Consider a compound slab consisting of two different materials having equal thickness and thermal conductivities K and 2K respectively. The equivalent thermal conductivity of the slab is
The temperature of the body is increased from – 73 0 C to 327 0 C , the ratio of energy emitted per second is
A black body has maximum wavelength λ m at temperature. 2000 K. Its corresponding wavelength at temperature 3000 K will be
The energy supply being cut-off, an electric heater element cools down to the temperature of its surroundings, but it will not cool further because
A body cools from 50 0 C to 49 o C in 5 sec . How long will it take to cool 40 0 C to 39 . 0 0 C ? Assume the temperature of surroundings to be 30 0 C and Newton ‘ s law of cooling to be valid :
A body of length 1 m having cross sectional area 0 . 75 m 2 has heat flow through it at the rate of 6000 Joule/sec. Then find the temperature difference if K = 200 J m – 1 K – 1
A solid cube and a solid sphere of the same material have equal surface area. Both are at the same temperature 120 0 C , then
The rate of cooling at 600 K, if surrounding temperature is 300 K is H. The rate of cooling at 900 K is
The maximum energy in the thermal radiation from a hot source occurs at a wavelength of 11 × 10 – 5 cm and temperature T 1. According to Wien’s law, the temperature of the source (on Kelvin scale) nT 1 for which the wavelength at maximum energy is 5 . 5 × 10 – 5 cm . The value of n is:
It takes 10 minutes to cool a liquid from 61 0 C to 59 0 C . If room temperature is 30 0 C then find the time taken in coolking from 51 0 C to 49 0 C
A calorimeter of mass 0.2 kg and specific heat 900 J / kg / K . Containing 0.5 kg of a liquid of specific heat 2400J/kg/K. Its temperature falls from 60 0 C to 55 0 C in one minute . Find the rate of cooling .
The intensity of radiation emitted by the sun has its maximum value at a wavelength of 510 nm and that emitted by the north star has the maximum value at 350 nm. If these stars behave like black bodies, then the ratio of the surface temperature of the sun and north star is
A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be
A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using
The total radiant energy per unit area, normal to the direction of incidence, received at a distance R from the centre of a star of radius r, whose outer surface radiates as a black body at a temperature TK is given by
A black body at 227 0 C radiates heat at the rate of 7 cal cm – 2 s – 1 . At a temperature of 727 0 C , the rate of heat radiated in the same units will be
A black body radiates 20 W at temperature 227 0 C . If temperature of the black body is changed o 727 0 C , then its radiating power will be:
Two identical metal balls at temperature 200 0 C and 400 0 C kept in air at 27 0 C . The ratio of net heat loss by these bodies
A body of length 1 m having cross sectional area 0.75 m 2 has heat flow through it at the rate of 6000 Joule/sec. Then find the temperature difference across it if K = 200 Jm – 1 K – 1
A solid cube and a solid sphere of the same material have equal surface area. Both are at the same temperature 120 0 C , then
The thermal emissivities of two bodies A and B are in the ratio of 1 e . The outer surface area of the bodies are same and they radiate energy at the same rate. Find the ratio of the wavelengths corresponding to the maximum spectral radiancy in the radiation from A to maximum spectral radiancy in the radiation from B:
A black body radiated maximum energy around a particular wavelength at a given temperature. If the temperature of the black body is now changed so that it radiates maximum energy around a wavelength n time the original wavelength (n<1) then power radiate by it will increases by a factor of
A body cools from 50 0 C to 49 0 C in 5 sec. How long will it take to cool from 40 0 C to 39 0 C ? Assume the temperature of surroundings to be 30 0 C and Newton’s law of cooling to be valid.
When the temperature of a black body increases, it is observed that the wavelength corresponding to maximum energy changes from 0.13 μ m to 0.26 μm . The ratio of the emissive powers of the body at the respective temperature is:
The radiation emitted by a star A is 1000 times that of the sun. If the surface temperatures of the sun and star A are 6000 K and 2000 K respectively, the ratio of the radii of the star A and the sun is:
The initial temperature of a body is 80 0 C . If its temperature falls to 64 0 C in 5 minutes and in n e x t 10 minutes to 52 0 . Find the temperature of surrounding.
A sphere and a cube of same material and same total surface area are placed in the same evacuated space turn by turn after they are heated to the same temperature. Find the ratio of their initial rates of cooling in the enclosure.
A spherical body of 2.0 cm diameter is maintained at 597 0 C . Assume that it radiates as if it were a blackbody, at what rate (in watts) is energy radiated from the sphere (approx)?
When two ends of a metal rod is kept at different temperatures, heat is conducted from hot end to cold end due to
A black body is at 727 0 C . It emits energy at a rate which is proportional to
A black body at 1227 0 C emits radiation with maximum intensity at a wavelength of 5000 A 0 . If the temperatures of the body is increased by 1000 0 c , the maximum intensity will be observed at
The surface temperature of the sun is T 0 and it is at average distance d from a planet. The radius of the sun is R. The temperature at which planet radiates the energy is
If λ m denotes the wavelength at which the radiative emission from a black body at a temperature T K is maximum, then
Equal volumes of water and alcohol when put in similar calorimeters take 100 sec and 74 sec respectively to cool from 50 0 C to 40 0 C . The thermal capacity of each calorimeter is numberically equal to the volume of either liquid. The specific gravity of alcohol is 0.8. If the specific heat capacity of water is 1 cal/gm, the specific heat capacity of alcohol will be
Three discs A, B and C having radii 2m, 4m, and 6 m respectively are coated with carbon black on their other surfaces. The wavelengths corresponding to maximum intensity are 300 nm, 400 nm and 500 nm, respectively. The power radiated by them are Q a , Q b and Q c respectively
A sphere of 3 cm radius acts like a black body. If it is in equilibrium with its surroundings and absorb 30 k watt of energy radiated to it from the surrounding. Then the temperature of the sphere will be
The rate of cooling at 600 K is H, if surrounding temperature is 300 K is H. The rate of cooling at 900 K is
A planet radiates heat at a rate proportional to the fourth power of its surface temperature T. If such a steady temperature of the planet is due to the exactly equal amount of heat received from the sun then which of the following statement is true?
A black body is heated from 7 0 C to 287 0 C . The ratio of radiation emitted is
The temperature of a body is increased by 50%. The amount of radiation emitted by it would be nearly
The rate of dissipation of heat by a black body at temperature T is Q. What will be the rate of dissipation of heat by another body at temperature 2T and emissivity 0.25?
A black body at high temperature T K radiates energy at the rate of EW / m 2 . When the temperature falls to ( T 2 ) K , the radiated energy will be:
Two spheres of the same material have radii 1 m and 4 m and temperature 4000 K and 2000 K respectively. The energy radiated per second by the first sphere is
A body is heated to a temperature of 227 o C and allowed to coal in air at 27 o C . Initial rate of cooling of the body is 1 o C / min what will be the rate of cooling of the body when its surface temperature is 127 o C ?
A metal rod AB of uniform cross sectional area is conducting heat from end A to end B and temperature difference between ends A and B is 100 o C . Mid point of the rod is C. Coefficient of thermal conductivity of the rod linearly increases from K C at end A to 2 K C at end B. Then temperature difference between A and C is
Two perfectly black spheres A and B having radii 8 cm and 2 cm are maintained at temperatures 127 o C and 527 o C respectively. The ratio of the energy radiated by A to that by B is
The high thermal conductivity of metal is due to free electrons. The relevant electron property is:
Under steady state the temperature of a body:
In which case does the thermal conductivity increases from left to right?
During severe winter in the low temperature zones of the world, the superficial parts of the lakes are frozen, leaving water below. The freezing at the bottom is prevented because:
A metallic rod is continuously heated at its two ends, the flow of heat through the rod does not depend upon:
Which of the following combinations of properties would.be most desirable for a cooking pot ?
If the temperature difference on the two sides of a wall increases from 100°C to 200°C, its thermal conductivity:
If equal quantities of ice melt completely in two identical containers in 30 and 20 minutes respectively, the thermal conductivities of the material of the two containers are in the ratio:
Two cylinders of the same diameter, one. of iron and the other of silver, are placed in. close contact as shown in Fig. If the thermal conductivity of silver is 11 times that of iron the temperature of the interface A is approximately:
A cylinder of radius R made of a material of thermal conductivity K 1 is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a material of thermal conductivity K 2 . The two ends of the combined system are maintained at two different temperatures. There is no loss of heat across the cylindrical surface and the system is in steady state. The effective thermal conductivity of the system is:
Three rods made of the same material and having the same cross-section have joined as shown in the Fig. Each rod is of same length. The left and right ends are kept at 0°C and 90°C respectively. The temperature of the junction of the three rods will be:
Fig. shows a conduction rod of non uniform cross-section. The ends of the rod are maintained at constant temperatures 100°C and 0°C respectively. At steady state, temperatures of P, Q, R and S are T p , T Q , T R and T s respectively, then:
A long metallic bar is carrying heat from one of its ends to the other end under steady state. The variation of temperature θ along the length x of the bar from its hot end is best described by which of the following figure?
Consider the rods of same length and different specific heats (s 1 ,s 2 ), conductivities ( k 1 ,k 2 ) and areas of cross-sections ( A 1 ,A 2 ) and both having temperature T 1 and T 2 at their ends. If the rate of loss of heat due to conduction is equal, then:
Consider a compound slab consisting of two different materials having equal thickness and thermal conductivities K and 2K, respectively. The equivalent thermal conductivity of the slab is:
A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. What is the amount of heat conducted by the new rod, when placed in thermal contact with the reservoirs in time t?
The two ends of a rod of length L and a uniform cross-sectional area A are kept at two temperatures T 1 and T 2 (T 1 > T 2 ). The rate of heat transfer, dQ dt through the rod in a steady state is given by:
A composite slab consists of two plates of thicknesses L 1 and L 2 and thermal conductivities K 1 and K 2 . The cross-sectional areas are equal. The equivalent thermal conductivity is:
A slab of stone of area 0.36 m 2 and thickness 0.1 m is exposed on the lower surface to steam at 100°C. A block of ice at 0°C rests on the upper surface of the slab. In 56 minutes 4.8 kg of ice is melted. The thermal conductivity of slab is: (Given latent heat of fusion of ice= 3.36 x 10 5 J kg -1 )
In steady state: (i) temperature does not change with time (ii) all parts of the body are at same temperature (iii) there is no flow of heat (iv) there is no absorption of heat
Two conductors having thicknesses d 1 and d 2 , thermal conductivities K 1 and K 2 are placed one above the other. The equivalent thermal conductance is:
The two ends of a metal rod are maintained at temperatures 100°C and 110°C The rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures 200°C and 210°C, the rate of heat flow will be :
Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K 1 and K 2 . The thermal conductivity of the composite rod will be
One end of a conducting rod is maintained at temperature 50 o C and at the other end ice is melting at 0 o C. The rate of melting of ice is doubled if
Water is usually heated by:
Ventilators are provided at the top of room:
Sun’s heat reaches us by:
A calorimeter full of hot water is hung in vacuum. It will:
The total radiation emitted by a perfectly black body is proportional to:
Energy E radiated per sec per unit area of a black body is given as E = σT 4 , σ is:
A metal piece is heated up to T K; the temperature of the surrounding is t K. The heat loss to the surrounding due to radiation is proportional to:
Two spherical black bodies of radii R 1 and R 2 having surface temperatures T 1 and T 2 respectively radiate the same powers; then R 1 /R 2 is equal to:
Two spheres of the same material have radii 1 m and 4 m and temperatures 4000 K and 2000 K respectively. The ratio of the energy radiated per second by the first sphere to that by the second is:
The temperature of a body is increased from 27°C to 127°C.The radiation emitted by it increases by a factor of:
A spherical body of emissivity e = 0.6 and area A and placed inside a perfectly black body is maintained at temperature T, then energy radiated per second will be:
Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t° C, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is:
A planet having average surface temperature T 0 at an average distance d from the sun. Assuming that the planet receives radiant energy from the sun only and it loses radiant energy only from the surface and neglecting all other atmospheric effects we conclude:
The amount of heat energy radiated by a metal at temperature T is E. When the temperature is increased to 3 T, energy radiated is:
If the temperature of the sun were to increases from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on earth to what it was previously, will be :
The energy radiated by a body depends on: (i) area of body (ii)m ass of body (iii) nature of surface (iv) temperature of body
Two identical objects A and B are at temperatures T A and T B respectively. Both objects are placed in a room with perfectly absorbing walls maintained at a temperature T (T A > T > T B ). The objects A and B attain the temperature T eventually. Select the correct statements from the following: (i) A only emits radiation, while B only absorbs it until both attain the temperature T (ii)A loses more heat by radiation than it absorbs, while B absorbs more radiation than it emits, until they attain the temperature T (iii) Both A and B only absorb radiation, but do not emit it,until they attain the temperature T (iv) Each object continues to emit and absorb radiation even after attaining the temperature T
For a black body at temperature 727°C, its radiating power is 60W and temperature of surrounding is 227° C. If temperature of black body is changed to 1227°C, then its radiating power will be :
A ball of surface temperature T is in thermal equilibrium with its environment . Which of the curve gives the energy E radiated by the sphere as a function of time ‘t’?
Newton’s law of cooling is used in the laboratory for determining:
A bucket fulI of hot water is kept in a room and it cools from 75 o C to 70 o in T 1 minute, from 70 o C to 65 o C in T 2 minute and from 65″C to 60″C in T 3 minute; then
A pan filled with hot food cools from 50.0 o C to 49.9 o C in 5 sec. How long with it take to cool from 40.0 o C to 39.9 o C if the room temperature is 30 o C?
A sphere, a cube and a disc all of the same material and of same volume are heated to 600 o C and left in air. Which of these will have the lowest rate of cooling?
Two circular discs A and B of same material with equal radii are blackened. They are heated to same temperature and are cooled under identical conditions. What inference do you draw from their cooling curves?
The rate of cooling of a body by radiation depends on: (i) area of body (ii) mass of body (iii) specific heat of body (iv) temperature of body and surroundings
A body cools from 80°C to 64°C in 5 min and same body cools from 80°C to 52°C in 10 min. What is the temperature of the surrounding?
Certain quantity of water cools from 70°C to 60°C in the first 5 minutes and to 54 °C in the next 5 minutes. The temperature of the surroundings is:
If there are two bodies at different temperatures, the wavelength of radiation (in which maximum radiation energy is distributed):
As the temperature of a black body increases, the wavelength of the emitted radiations of maximum intensity:
According to Wien’s displacement law:
black body has wavelength λ m corresponding to maximum energy at 2000 K. Its wavelength corresponding to maximum energy at 3000 K will be:
black body is at a temperature of 2880 K. The energy of radiation emitted by this object with wavelength between 499 nm and 500 nm is U 1 , between 999 nm and 1000 nm is U 2 and between 1499 nm and 1500 nm is U 3 . The Wien’s constant b = 2.88 x 10 6 nm K. Then:
Cloudy nights are warmer than starry ones because:
The colour of a star is an indication of its:
The temperature of the surface of the sun can be inferred from a study of the:
The spectral energy distribution of the sun (temperature 6050 K) has a maximum at 4 753 A. The temperature of a star for which this maximum is at 9506 A, is:
The surface temperature of the sun which has maximum energy emission at 500 nm is 6000 K. The temperature of a star which has maximum energy emission at 400 nm will be:
Shown below are the black body radiation curves at temperature T 1 and T 2 (T 2 > T 1 ) Which of the following plots is correct ?
Consider the following statements. (A) Water cannot be boiled inside a satellite by convection. (B) In weightlessness conditions, natural movement of heated fluid is not possible.
Consider the following statements. (A) Snow is better insulator than ice. (B) Snow contain air packets and air is a bad conductor of heat. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Animals curl into a ball, when they feel very cold. (B) Animals by curling their body reduces the surface area of the body. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Heat radiations and light have identical properties. (B) A cold body does not radiate heat to the hotter surroundings. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) For an ideal black body, both absorption coefficient and reflection coefficient are one. (B) Perfect absorbers are perfect reflectors. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) sphere, a cube and a thin circular plate made of same material and of same mass are initially heated to 200° C, the plate will cool at fastest rate. (B) Rate of cooling = eAσ ms ( T 4 – T 0 4 ) ∞ surface area Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Thermal radiation is the fastest mode of heat transfer. (B) Thermal radiation is always transmitted in straight line path.· Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Water cannot be boiled inside a satellite by convection. (B) In weightlessness conditions, natural movement of heated fluid is not possible. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) A brass tumbler feels much colder than a wooden tray on a chilly day. (B) The thermal conductivity of brass is more than that of wood. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) A body with large reflectivity is a poor emitter of heat radiations. (B) A body with large reflectivity is a poor absorber of heat. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) For higher temperature, the peak emission wavelength of a black body shifts to lower wavelengths. (B) Peak emission wavelength of a black body is proportional to the forth power of its absolute temperature.
Consider the following statements. (A) If temperature of any body is increased by 10%, then there will be 40% increase in amount of radiation from its surface. (B) Equation ∆ E E = 4 ∆ T T also true for large percentage increase where E ∞ T 4 . Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) The equivalent thermal conductivity of two plates of same thickness in contact (series) is less than the smaller value of thermal conductivity. (B) For two plates of equal thickness in contact (series), the equivalent thermal conductivity is given by 1 K = 1 K 1 + 1 K 2 Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Greater the coefficient of thermal conductivity of a material, smaller is the thermal resistance of a rod of that material. (B) Thermal resistance of a body is the ratio of temperature difference between the ends of the body and rate of flow of heat. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
The spectrum of a black body at two temperatures 27°C and 327°C is shown in the figure. Let A 1 and A 2 be the areas under the two curves respectively. Find the value of A 2 A 1 .
Consider the following statements. (A) A man would feel iron or wooden balls equally hot at 37.4°C. (B) At 37.4°C both iron and wood have same thermal conductivity. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) The bulb of one thermometer is spherical while that of the other is cylindrical. Both have equal amount of mercury. The response of the cylindrical bulb thermometer will be quicker. (B) Heat conduction in body is directly proportional to cross-sectional area. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Coolant coils are fitted at the top of a refrigerator, for formation of convection current. (B) Air becomes denser on cooling. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) When temperature difference across the two sides of a wall is increased, its thermal conductivity increases. (B) Thermal conductivity depends upon the temperature difference across the two sides of a wall. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
Consider the following statements. (A) Metals have high thermal conductivity. (B) Metals have free electrons. Select the correct option. (a) (A) is false but (B) is true. (b) Both (A) and (B) are true. (c) (A) is true but (B) is false. (d) Both (A) and (B) are false.
The quantity of heat which crosses-unit area of a metal plate during conduction depends upon:
According to Ingen Hauz’s experiment the thermal conductivity 1 and length L of the metal rod up to which the wax melts are ·related as:
In the Ingen Hauz’s experiment the wax melts up to lengths 10 and 25 cm on two identical rods of different materials. The ratio of thermal conductivities of the two materials is:
A 2 cm thick slab of commercial thermocole, 100 cm 2 in cross-section and having thermal conductivity 2 x 10 -4 cal sec -1 cm -1 (C o ) -1 has insulating regions differing by 100°C. The quantity of heat flowing through it in a day will be:
One end of a copper rod of length 1.0 m and area of cross-section 10 -3 m 2 is immersed in boiling water and the other end in ice. If the coefficient of thermal conductivity of copper is 92 cal/m-s-C 0 and the latent heat of ice is 8 x 10 4 cal/kg, then the amount of ice which will melt in one minute is:
A metal bar of length / is covered with some non-conducting material to prevent heat losses from its surface and the two ends are maintained at steady temperatures θ 1 and θ 2 ( < θ 1 ) . In the steady state, the temperature θ of the bar above the surrounding at distance x from the hot end varies as shown in the graph:
Two walls of thicknesses d 1 and d 2 and thermal conductivities K 1 and K 2 are in contact. In the steady state, if the temperatures at the outer surface are T 1 and T 2 , the temperature at the common wall is:
A solid sphere and a hollow sphere of the same material and of equal radii are heated to the same temperature. Then select the wrong statement.
Suppose the sun expands so that its radius becomes 100 times its present radius and its surface temperature becomes half of its present value. The total energy emitted by it then will increase by a factor of :
If the temperature and radius of Sun are doubled and the average distance of earth from the sun is also doubled then power received by earth will be
Three rods each of same length and cross section are joined in series. The thermal conductivity of the materials are k, 2k and 3k respectively. If one end is kept at 300 0 C and the other at 100 0 C. What would be the temperature of the junction which comes before the end at 100 0 C in the steady state. Thermal conductivity of copper is 400 WmK -1 .
Two spheres, A & B, are made up of the same material. The radius of A is twice that of B, while the temperature of A is half that of B. What is their ratio of energy emitted per unit time (E A : E B )?
An ice cube is kept on the surface of an aluminium block and another ice cube on the surface of a plastic block. Both blocks have the same temperature . Select the correct statement.
The temperature of the two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity k and 2 K and thickness x and 4 x respectively are T 2 and T 1 (T 2 > T 1 ). The rate of heat transfer through the slab, in a steady-state is A T 2 − T 1 K x f with f equal to:
Equal temperature difference exists between the ends of two metallic rods 1 and 2 of equal length. Their thermal conductivities are K 1 and K 2 and cross-sectional areas are respectively A 1 and A 2 The condition for equal rate of heat transfer will be
Two metallic rods are connected in series. Both are of same material, of same length and same area of cross-section. If the conductivity of each rod be K, then what will be the conductivity of the combination ?
Heat is flowing through two cylindrical rods of the same material. The diameters of the rods are in the ratio 1 : 2 and the lengths in the ratio 2 : 1. If the temperature difference between the ends is same, then ratio of the rate of flow of heat through them will be
Two rods of same material, cross-section and length are welded end to end. The temperature difference across the ends of the composite rod is 100°C. 1o cal. of heat flows through the combination in 10 min. If the rods are welded side by side, how much time will 10 cal heat take to go across the combination ?
Two walls of thickness d 1 and d 2 and thermal conductivities K 1 and K 2 are in contact. In the steady state, if the temperatures at the outer surfaces are T 1 and T 2 the temperatures at the common wall is
A rod CD of thermal resistance 5.0 K/W is joined at the middle of an identical rod AB as shown in fig. The ends A, B and D are maintained at 100°C, 0°C and 25°C respectively. The temperature of junction C will be
The temperature of the two outer surfaces of a composite slab consisting of two materials having coefficients of thermal conductivity K and 2K and thickness x and 4x, respectively are T 2 and T 1 (T 2 >T 1 ). The rate of heat transfer through the slab, in steady state is KA T 2 − T 1 X f with f equal to
A body initially at 60°C cools to 50°C in 10 min. What will be its temperature at the end of next 10 min. if the room temperature is 25°C. Assume Newton’s law of cooling
Three discs A, B and C having radii 2 m, 4 m and 6 m respectively are coated with carbon black on their outer surfaces. The wavelengths corresponding to maximum intensity are 300 nm, 400 nm and 500 nm respectively. The power radiated by them are Q A ,Q B and Q C respectively.
According to Newton’s law of cooling, the rate of cooling of a body is proportional to ( Δθ ) n , where ∆ θ is the difference of temperature of the body and the surroundings and n is equal to
Two bodies A and B have thermal emissivities of 0.01 and 0.81 respectively. The outer surface areas of the two bodies are the same. The two bodies emit total radiant power at the same rate. The wavelength λ B corresponding to maximum spectral radiancy in the radiation from B is greater than the wavelength I, corresponding to maximum spectral radiancy in the radiation from A by 1.00 μ m. If the temperature of A is 5802 K
A point source of heat of power P is placed at the centre of a spherical shell of mean radius fi. The material of the shell has thermal conductivity K. If the temperature difference between the outer and inner surface of the shell is not to exceed L the thickness of the shell should not be less than
Three stars A, B and C appear as green, red and blue respectively. The star having minimum temperature is
The tungsten filament of an electric lamp has a surface area A and a power rating P. If the emissivity of the filament is e and σ is Stefan’s constant, the steady temperature of the filament will be
Two spheres of the same material have radii 1 m and 4 m and temperatures 4000 K and 2000 K respectively. The energy radiated per second by the first sphere is
All bodies radiate heat in proportion to the fourth power of temperature T. If a body (coated black) at 400 K surrounded by atmosphere at 300 K has cooling rate r 0 , the same body at 900 K, surrounded by the same atmosphere, will have cooling rate closest to
A black body of surface area 10 cm 2 is heated to 127°C and is suspended in a room at temperature 27°C. The rate of loss of heat is
The rate of heat radiation from two patches of skin each of area S, on a patient’s chest differ by 2%. lf the patch of the lower temperature is at 300 K and the emissivity of both the patches is assumed to be unity, the temperature of the other patch is closest to
Three discs A, B and C having radii 2 m, 4 m and 6 m respectively are coated with carbon black on their outer surfaces. The wavelengths corresponding to maximum intensity are 300 nm, 400 nm and 500 nm respectively. The power radiated by them are Q A ,Q B and Q C respectively.
A spherical body of area A and emissivity e = 0 .6 is placed inside a perfectly black body’ The heat radiated by the body at temperature T is
Two spheres of the same material have radii 1 m and 4 m and temperatures 4000 K and 2000 K respectively. The energy radiated per second by the first sphere is
Two rods (one semi-circular and other straight) of same material and of same cross-sectional area are joined as shown in fig. The point A and B are maintained at different temperatures. The ratio of the heat transferred through a cross-section of a semicircular rod to the heat transferred through a cross-section of the straight rod in a given time is
Fig. shows a system of two concentric spheres of radii r 1 and r 2 kept at temperatures T 1 and T 2 respectively. The radial rate of flow of heat in a substance between the two concentric spheres is proportional to
A body takes t minutes to cool from 62°C to 61°C when the surrounding temperature is 30°C. The time taken by the body to cool from 46°C to 45.5°C is
A perfect black body emits radiation at temperature T 1 K. If it is to radiate 16 times this power, its temperature T 2 will be
A metal piece is heated to T 1 K. The temperature of the surroundings is T 2 K. The heat in the surroundings due to radiation is proportional to
If the temperature of the sun is doubled, the rate of energy received on earth will be increased by a factor
Two spheres P and Q of same colour having radii 8 cm and 2 cm are maintained at temperature 727°C and 527°C respectively. The ratio of energy radiated by P and Q is
Two rods of same material, cross-section and length are welded end to end. The temperature difference across the ends of the composite rod is 100°C. 10 cal of heat flows through tie combination in 10 minutes. lf the rods are welded side by side how much time will 10 cal heat take to go across the combination ?
The maximum wavelength of radiation emitted at 2000 K is 4 μ m. What will be the maximum wavelength of radiation emitted at 2400 K
The plots of intensity versus wavelength for three black bodies at temperature T 1 , T 2 and T 3 respectively are as shown. Their temperatures are such that
An ideal black-body at room temperature is thrown into a furnace. It is observed that
The graph shown in fig. represents the variation of temperature 7 of two bodies x and y having same surface area with time t due to the emission of radiation. The correct relation between the emissivity and absorptivity power of two bodies is
A heated body emits radiation which has maximum intensity at frequency v m . If the temperature of the body is doubled,
The energy spectrum of a black body exihibits maximum around a wavelength λ o . The temperature of the black body is now changed such that the energy is maximum around a wavelength 3 λ o / 4 . The power radiated by the black body will now increase by a factor of
If the temperature of the sun were to increase from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on earth to what it was previously will be
Fig. shows a conduction rod of non uniform cross-section. The ends of the rod are maintained at constant temperatures 100°C and 0°C respectively. At steady state, temperatures of P, Q, R and S are T p , T Q , T R and T s respectively, then:
A piece of iron is heated in a flame. If at first it becomes dull red, then becomes reddish, yellow and finally turns to white hot. The correct explanation for the above observation is possible by using
The thickness of a metallic plate is 0.4 cm. The temperature between its two surfaces is 20 0 C. The quantity of heat flowing per second is 50 cal from 5 cm 2 area. The coefficient of thermal conductivity (in CGS system) will be
On observing light from three different stars P , Q and R, it was found that intensity of violet color is maximum in the spectrum of P , the intensity of green color is maximum in the spectrum of Rand the intensity of red color is maximum in the spectrum of Q . If T P , T Q and T R are the respective absolute temperatures of P , Q and R , then it can be concluded from the above observations that
A liquid cools from 50 0 C to 45 0 C in 5 min and from 45 0 C to 41.5 0 C in the next 5 min. The temperature of the surrounding is
A body cools from 50 0 C to 40 0 C in 5 min. The surrounding temperature is 20 0 C. In what further time (in minute) will it cool to 30 0 C?
A cylinder of radius R made of a material of thermal conductivity K 1 is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a material of thermal conductivity K 2 . The two ends of the combined system are maintained at two different temperatures. There is no loss of heat across the cylindrical surface and the system is in steady state. The effective thermal conductivity of the system is
A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at wavelength 250 nm is U 1 , at wavelength 500 nm is U 2 and that at 1000 nm is U 3 . Wien’s constant, b = 2.88 X 10 6 nmK. Which of the following is correct?
A black body with surface area 0.001 m 2 is heated up to a temperature 400 K and is suspended in a room temperature 300 K .The initial rate of loss of heat from the body to room is
Certain quantity of water cools from 70 0 C to 60 0 C in the first 5 min and to 54°C in the next 5 min. The temperature of the surrounding is
A body cools from 80°C to 64°C in 5 min and same body cools from 80°C to 52°C in 10 min. What is the temperature of the surrounding?
A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t . The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. What is the amount of heat conducted by the new rod when placed in thermal contact with the two reservoirs in time t?
A cylindrical rod having temperatures T 1 and T 2 at its ends. The rate of flow of heat is Q 1 cal/sec. If all the dimensions are doubled keeping T 1 and T 2 constant, then rate of flow of heat Q 2 will be:
Two identical rods AC and CB made of two different metals having thermal conductivities in the ratio 2 : 3 are kept in contact with each other at the end C.as shown in the Fig. A is at 100°C and B is at 25°C. Then the junction C is at :
Two identical conducting rods are first connected independently to two vessels, one containing water at 100 0 C and the other containing ice at 0 0 C. In the second case, the rods are joined end-to-end and connected to the same vessels. Let q 1 and q 2 gs -1 be the rate of melting of ice in two cases, respectively. The ratio of q 1 q 2 is
Two identical plates of metal are welded end to end as shown in figure (A); 20 cal of heat flows through it in 4 minutes. If the plates are welded as shown in figure (B), the same amount of heat will flow through the plates in
A black body has maximum wavelength λ m at 2000 K. Its corresponding wavelength at 3000 K will be
Three rods made of the same material and having the same cross-section have been joined as shown in the figure. Each rod is of the same length. The left and right ends are kept at respectively. The temperature of the junction of the three rods will be
In a composite rod, when two rods of different lengths and of the same area of cross-section are joined end to end, then if K is the effective coefficient of thermal conductivity, I 1 + I 2 K is equal to
