Important Questions for CBSE Class 12 Physics Electromagnetic Waves

# Important Questions for CBSE Class 12 Physics Electromagnetic Waves

Important questions for CBSE Class 12 Physics Chapter 8 – Electromagnetic Waves Chapter 8 is crucial in the CBSE Class 12 Physics syllabus, so we’ve provided these questions and answers to help students prepare effectively. Use this study material to excel in your Class 12 Physics exam.

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Expert Physics teachers have prepared the Important Questions with answers for CBSE Class 12 Physics Chapter 8 – Electromagnetic Waves from the latest edition of CBSE NCERT books. You can download more Important Questions Class 12 Physics Chapter 12 PDF for free from Infinity Learn -Learning App.

 CBSE Class 12 Physics Important Questions S.No Chapter No Chapter Name 1 Chapter 1 Electric Charges and Fields 2 Chapter 2 Electrostatic Potential and Capacitance 3 Chapter 3 4 Chapter 4 Moving Charges and Magnetism 5 Chapter 5 Magnetism And Matter 6 Chapter 6 Electromagnetic Induction 7 Chapter 7 Alternating Current 8 Chapter 8 Electromagnetic Waves 9 Chapter 9 Ray Optics and Optical Instruments 10 Chapter 10 Wave Optics 11 Chapter 11 Dual Nature of Radiation and Matter 12 Chapter 12 Atoms 13 Chapter 13 Nuclei 14 Chapter 14 Semiconductor Electronic: Material, Devices And Simple Circuits 15 Chapter 15 Communication System

## Important Questions for CBSE Class 12 Physics Electromagnetic Waves

1.Displacement Current The current which comes into play m the region in which the electric field and the electric flux is changing with time. It is given by

2.Need for Displacement Current Ampere’s circuital law for conduction current during charging of a capacitor was found inconsistent. Therefore, Maxwell modified Ampere’s circuital law.

3.The displacement current produces in space due to change of electric flux linked with the surface. This reveals that, varying electric field is the source of magnetic field.

4.Maxwell’s Equations of Electromagnetic Waves Maxwell’s equations are the basic laws of electricity and magnetism. These equations give complete description of ail electromagnetic interactions.

5. Electromagnetic Waves An electromagnetic wave is a wave radiated by an accelerated or oscillatory charge in which varying magnetic field is the source of electric field and varying electric field is the source of magnetic field. Thus two fields becomes source of each other and the wave propagates in a direction perpendicular to both the fields.

6. Electromagnetic waves are transverse in nature, i.e. electric and magnetic fields are perpendicular to each other and to the direction of wave propagation. Electromagne­tic waves are not. deflected by electric and magnetic fields.

7. E (electric field) and B (magnetic field) in electromagnetic waves are in same phase.

8. Speed of electromagnetic wave

9. The energy in electromagnetic wave is divided on average equally between electric and magnetic fields.

10. Energy associated with an electromagnetic wave is

11. Linear momentum delivered to the surface p= U/c

where, U = total energy transmitted by electromagnetic waves and c = speed of electromagnetic wave

12. Electromagnetic Spectrum The systematic sequential distribution of electromagnetic waves in ascending or descending order of frequency or wavelength is known as electromagnetic spectrum. The range varies from 10-12 m, to 104 m, i.e. from y-rays to radio waves.

13. Elementary facts about the uses of electromagnetic waves

• In radio and TV communication.
• In astronomical field.

Microwaves

• In analysis of molecular and atomic structure.
• For cooking purpose.

Infrared waves

• In knowing molecular structure.
• In remote control of TV VCR, etc. Ultraviolet rays

Ultraviolet rays

• Used in burglar alarm.
• To kill germs in minerals.

X-rays

• In medical diagnosis as they pass through the muscles not through the bones.
• In detecting faults, cracks, etc., in metal products,

14. The optical effect is produced by electric field vector of the electromagnetic waves.

## Previous Years’ Examination Questions

### 1 Mark Questions

1.To which part of the electromagnetic spectrum does a wave of frequency 5 x 1019 Hz belong? [All India 2014]

Ans

2. To which part of the electromagnetic spectrum does a wave of frequency 3 x 1013 Hz belong? [All India 2014]

Ans

3. Write the condition under which an electron will move undeflected in the presence of crossed electric and magnetic fields. [All India 2014c]

Ans

4.Welders wear special goggles or face masks with glass windows to protect their eyes from electromagnetic radiation. Name the radiations and write the range of their frequency. [All India 2013]

Ans

5.What are the directions of electric and magnetic field vectors relative to each other and relative to the direction of propagation of electromagnetic waves? [All India 2012]

Ans

6.Name the electromagnetic waves which
(i) maintain the earth’s warmth and
(ii) are used in aircraft navigation. [Foreign 2012]
Ans

7.A plane electromagnetic wave travels in vacuum along Z- direction. What can you say about the direction of electric and magnetic field vectors? [Delhi 2011]

Ans

8.Write two uses of microwaves. [Foreign 2011]
Ans

9. Write two uses of infrared rays. [Foreign 2011]

Ans

10.Write two uses of X-rays. [Foreign 2011]

Ans

11.What is the frequency of electromagnetic waves produced by oscillating charge of frequency V=105Hz? [Delhi 2011C]

Ans

12.How are infrared waves produced? What is the range of their wavelength? [Delhi 2010c]

Ans

13.Which of the following has the shortest wavelength? Microwaves, ultraviolet rays, X-rays. [All India 2010]

Ans

14. Arrange the following in descending order of wavelength. X-rays, radiowaves, blue light, infrared light. [All India 2010]

Ans

15. Which part of electromagnetic spectrum has largest penetrating power? [Delhi 2010]

Ans

16. Which part of electromagnetic spectrum is absorbed from sunlight by ozone layer? [Delhi 2010]
Ans

Also Check: CBSE Class 12 Physics Answer Key 2024 | CBSE CBSE Class 12 Physics Paper Analysis 2024

17. Which part of electromagnetic spectrum is used in RADAR systems? [Delhi 2010]

Ans Micro Waves

18.Name the electromagnetic radiation used to destroy cancer cells and write its frequency range. [Foreign 2010]

Ans

19.In what way, are the directions of the electric and magnetic field vectors representing an electromagnetic wave related to each other? [Delhi 2010c]\

Ans

20.Express the velocity of propagation of an electromagnetic waves in terms of the peak value of the electric and magnetic fields. [All India 2010C]

Ans

21. A capacitor has been charged by a dc source. What are the magnitudes of conduction and displacement currents, when it is fully charged? (Delhi 2013)

Ans. After being fully charged, the source will maintain the potential across the plates, resulting in zero magnitudes of displacement current and conduction current.

22.Write the following radiations in ascending order in respect of their frequencies X-rays, microwaves, ultraviolet rays and radiowaves. [Delhi 2009]

Ans

23. Name the electromagnetic radiation to which waves of wavelength in the range of 10-2 m belongs. Give one use of this part of electromagnetic spectrum. [Delhi 2009, 2008]

Ans

24. Name the electromagnetic radiation which can be produced by a klystron or a magnetron valve. [Foreign 2009]

Ans

25. Why is ozone layer on top of the stratosphere crucial for human survival? [All India 2009C]

Ans

26. State the reason why microwaves are best suited for long distance transmission of signals. [Foreign 2008]

Ans

27.Special devices like the klystron valve or the magnetron valve, are used for production of electromagnetic waves. Name these waves and also write one of their applications. [Delhi 2008C]

### 2 Marks Questions

28.

(a) How does oscillating charge produce electromagnetic waves?

(b) Sketch a schematic diagram depicting oscillating electric and magnetic fields of an EM wave propagating along positive Z-direction. [Foreign 2014]

Ans

29.

(i) How are electromagnetic waves produced?

(ii) How do you convince yourself that electromagnetic waves carry energy and momentum? [Delhi 2013c]

Ans

30.(i) Arrange the following electromagnetic waves in the descending order of their wavelengths.

• Microwaves
• Infrared rays
• y-rays

(ii) Write one use each of any two of them. [Delhi 2013C]

Ans

31.

(i) An electromagnetic wave is travelling in a medium, with a velocity v = vi. Draw a sketch showing the propagation of the electromagnetic wave, indicating the direction of the oscillating electric and magnetic fields.

(ii) How are the magnitudes of the electric and magnetic fields related to velocity of the electromagnetic wave? [HOTS; Delhi 2013; All India 2008C]
Ans

32. A capacitor of capacitance C is being charged by connecting it across a DC source along with an ammeter. Will the ammeter show a momentary deflection during the process of charging? If so, how would you explain this momentary deflection and the resulting continuty of current in the circuit? Write the expression for the current inside the capacitor. [All India 2012]

Ans.

33. Arrange the following electromagnetic radiations in ascending order of their frequencies:

(i) Microwave

(iii) X-rays

(iv) Gamma rays

Write two uses of any one of these. (Delhi 2009)

Ans. In ascending order of their frequencies :

Radiowave < Microwave < X-rays < Gamma rays.

Two uses of microwaves are-

1. In microwave ovens

34.Explain briefly how electromagnetic waves are produced by an oscillating charge? How is the frequency of the electromagnetic waves produced related to that of the oscillating charge? [Foreign 2012]

Ans

35. Name the constituent radiation of electromagnetic spectrum which is used for

• studying the crystal structure Write the frequency range for each. [Delhi 2011C]

Ans

36.Draw a sketch of a plane electromagnetic wave propagating along the Z-direction. Depict clearly the directions of electric and magnetic fields varying sinusoidally with Z. [All India 2011]

37. Arrange the following electromag­netic radiations in ascending order of their frequencies.

• Microwaves
• X-rays
• y-rays

Write two uses of any one of these. [Delhi 2010]

Ans.

38. How are X-rays produced? Write their two important uses. [Foreign 2010;Delhi 2010]

Ans

39. How are infrared rays produced? Write their two important uses. [Foreign 2010; All India 2010 C]

Ans.

40.How are microwaves produced? Write their two important uses. [Foreign 2010]

Ans

• Optical and radio telescopes are built on the ground while X-ray astronomy is possible only from satellites orbiting the earth. Why?
• The small ozone layer on top of the stratosphere is crucial for human survival. Why? [All India 2009]

Ans

42. How does a charge, q oscillating at certain frequency produce electromagnetic waves? Sketch a schematic diagram depicting electric and magnetic fields for an electromagnetic wave propagating along the Z- direction. [Delhi 2009]

Ans

43.Name the electromagnetic radiations having the wavelength range from 1 mm to 700 nm. Give its two important applications. [Foreign 2009]

Ans.

44.Name the electromagnetic radiation having the wavelength range from 10-1 m to 10~3 Give its two important applications. [Foreign 2009]

Ans.

45.Name the electromagnetic radiations having the wavelength range from 1 nm to 10~3 Give its two important applications. [Foreign 2009]
Ans

46.Identify the different types of electromagnetic radiations, which are used

• to kill germs,
• for physical therapy. [All India 2009c]

Ans

47. In an electromagnetic wave, the oscillating electric field having a frequency of 3 x 1010 Hz and an amplitude of 30 V/m propagates in the positive X-direction.

• What is the wavelength of the electromagnetic wave?
• Write down the expression to represent the corresponding magnetic field. [Foreign 2008]

Ans

48. The following table gives the wavelength range of some constituents of the electromagnetic spectrum.

 S. No. Wavelength range 1. 1 nm to 700 nm 2. 400 nm to 1 nm 3. 1 nm to10-3 nm 4. <10“3 nm

Select the wavelength range and name of the electromagnetic waves that are

• widely used in the remote switches and household electronic devices.
• produced in nuclear reactions. [Delhi 2008C]

Ans

### 3 Marks Questions

• Name the waves which are produced during radioactive decay of a nucleus. Write their frequency range.
• Welders wear special glass goggles while working. Why? Explain.
• Why are infrared waves often called as heat waves? Give their one application. [Delhi 2014]

Ans.

(i) Name the EM waves which s suitable for radar systems used in aircraft navigation. Write the range of frequency of these waves.

(ii) If the earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now? Explain.

(iii) An EM wave exerts pressure on the surface on which it is incident. Justify. [Delhi 2014]

Ans

• Name the EM waves which are used for the treatment of certain forms of cancer. Write their frequency range.
• Thin ozone layer on top of stratosphere is crucial for human survival. Why?
• Why is the amount of the momentum transferred by the EM waves incident on the surface so small? [Delhi 2014]

Ans

• Show, by giving a simple example, how EM waves carry energy and momentum.
• How are microwaves produced? Why is it necessary in microwaves ovens to select the frequency of microwaves to match the resonant frequency of water molecules?
• Write two important uses of infrared waves. [Delhi 2014 c]

Ans.

53. (i) Describe briefly how electromagnetic waves are produced by oscillating charges? (ii) Give one use of each of the following.

• Microwaves
• Ultraviolet rays
• Infrared rays
• y-rays [HOTS; All India 2011c]

Ans.

54.How are electromagnetic waves produced by oscillating charges? Why is it not possible to produce electromagnetic waves in the visible region with modern electronic circuits in the laboratory? What is the method of production of X-rays? [Delhi 2009C]

Ans.

55. Identify the following electromagnetic radiations as per the wavelengths given below. Write one application of each.

• 10-3 nm
• 10-3 m
• 1 nm [All India 2008]

Ans

56. Identify the following electromagnetic radiations as per the frequencies given below. Write one application of each.

• 1020 Hz
• 1012 Hz
• 10n Hz [All India 2008]

Ans.

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