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Chapter: 12th Physics : Electromagnetic Waves

Electromagnetic Waves: Questions and Answers

Physics : Electromagnetic Waves: Important Questions, Short answer questions , Long answer questions

Short answer questions

1. What is displacement current?

The displacement current can be defined as the current which comes into play in the region in which the electric field or the electric flux is changing with time

id = ε0  [/dt]

2. What are electromagnetic waves?

Electro magnetic waves are non - mechanical waves which move with speed equals to the speed of light (in vacuum). It is a transverse wave.

3. Write down the integral form of modified Ampere’s circuital law.

The modified Ampere's circuital law is also known as Ampere -Maxwell's law.

This law relates the magnetic field around any closed path to the conduction current and displacement current through that path.

4. Write notes on Gauss's law in magnetism.

Gauss's law in magnetism is the surface integral of magnetic field over a closed surface is zero.


5. Give two uses each of (i) IR radiation,

(ii) Microwaves and (iii) UV radiation.

i) Uses of IR radiation: (any Two)

 It provides electrical energy to satellites by means of solar cells.

 It is used to produce dehydrated fruits.

Heat therapy for muscular pain or sprain.

 In TV remote as a signal carrier

To look through haze fog or mist.

In night vision or infrared photography

ii) Uses of Microwaves: (Any Two)

❖ In RADAR system for aircraft navigation.

 To find speed of the vehicle.

❖ In microwave oven for cooking.

❖ In very long distance wireless communication through satellites.

iii) Uses of UV radiation: (Any two)

 To destroy bacteria in sterilizing the surgical instruments.

In burglar alarm

To detect the invisible writing, finger prints

In the study of atomic structure.


6. What is meant by Fraunhofer lines? How are they useful in the identification of elements present in the Sun?

When the spectrum obtained from the sun is examined, it consists of large number of dark lines. These dark lines in the solar spectrum are known as Fraunhofer lines.

The absorption spectra for various materials are compared with the Fraunhofer lines in the solar spectrum, which helps in identifying elements present in the sun's atmosphere.


7. Write notes on Ampere-Maxwell law.

Maxwell modified Ampere's law as

 Where the total current enclosed by the surface becomes the sum of conduction current and displacement current, ie, i = ic + id.

The above equation (1) is known as Ampere- Maxwell law.


8. Why are electromagnetic waves are called non-mechanical waves?

According to Maxwell, the variation in electric and magnetic fields perpendicular to each other, produces electromagnetic disturbances in space. These disturbances have the properties of a wave ie, electromagnetic waves and propagate through space without any material medium. So electromagnetic wave is a non-mechanical wave.

Long answer questions

1. Write down Maxwell equations in integral form.

2. Write short notes on (a) microwave (b) X-ray (c) radio waves (d) visible spectrum

3. Discuss the Hertz experiment.


Discuss briefly the experiment conducted by Hertz to produce and detect electromagnetic spectrum.

4. Explain the Maxwell’s modification of Ampere’s circuital law.

5. Explain the importance of Maxwell's correction.

6. Write down the properties of electromagnetic waves.

7. Discuss the source of electromagnetic waves.

8. Explain the types of emission spectra.

9. Explain the types of absorption spectra.

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