 # Characteristics of EM Waves Questions

## What are Electromagnetic Waves?

When an electric field comes in contact with the magnetic field, electromagnetic waves are produced, and these electromagnetic waves are also known as EM waves. Electromagnetic radiations are composed of electromagnetic waves. Also, one more phenomenon that is responsible for the formation of electromagnetic waves is the oscillating electric and magnetic fields. Electromagnetic waves are fundamental equations of electrodynamics and a solution of Maxwell’s equations.

### Formation of Electromagnetic Waves

When an electric field comes in contact with a magnetic field, then electromagnetic waves are formed. The electric field and magnetic field of an electromagnetic wave are perpendicular to the direction of the EM and are also at right angles to each other, that is, perpendicular to each other.

In vacuum, EM waves travel with a constant velocity, that is, 3.00 x 108 ms-1. EM waves have the capability to show interference or diffraction, and also, they are neither deflected by the electric field nor by the magnetic field. An electromagnetic wave can travel through any medium air, solid or vacuum basically, and it does not need a medium to propagate from one place to another. Sound waves or water waves (mechanical waves), on the other hand, require a medium to travel. EM waves are measured by their amplitude and wavelength; this means that they are. ‘transverse’ waves.

Electromagnetic waves can be divided into a range of frequencies where the highest point of a wave is termed as ‘crest’, whereas the lowest point is termed as ‘trough’. This is known as the electromagnetic spectrum. Some examples of EM waves are X-rays, radio waves, gamma rays, etc.

### Characteristics of Electromagnetic Waves

Some important characteristics and properties of electromagnetic waves are listed below –

• As the EM waves propagate by fluctuating the electric and magnetic fields such that the two fields are perpendicular to each other, this means that the Electromagnetic waves are transverse in nature.
• The reason behind the production of electromagnetic waves is the accelerating charged particle.
• Electromagnetic waves possess a constant velocity nearly equal to 3×108ms−1 in vacuum, and it is denoted by C = 1/√μoϵo.
• The propagation of electromagnetic waves does not require any material medium to travel.
• Frequency is the most essential characteristic of an electromagnetic wave. When a wave travels from one medium to another, its frequency remains unchanged, but its wavelength changes.
• The refractive index of a material can be written as n = √μrϵr
• The principle of superposition is followed by electromagnetic waves.
• The optical effects due to an electromagnetic wave happen because of the light vector.
• The velocity of the electromagnetic wave can be determined as the ratio of the amplitudes of electric and magnetic fields, that is, C = E0/B0; also in an electromagnetic wave, the magnetic and electric fields with their magnitudes having constant ratio are in the same phase.
• The electric energy (uE) and the magnetic energy (uM) carried by the electric and magnetic fields of electromagnetic waves are equal, that is; uE = uM.
• The vector S, which represents the energy transferred by electromagnetic waves per second per unit area, is given by S→ = 1/μ (E→ x B→)

### Important Questions on Characteristics of EM Waves

(a) Since the wavelength is given by λ= c/v

## (b) Bo = Eo /c = 51/3×108 = 17×10-8 T

2) Calculate the wavelength of electromagnetic waves of frequency 8×102Hz in free space. Also, give two applications of the type of wave.

It is given that,

V= 8×1012Hz

Using λ=c/v

λ=3×108/8×1012

λ= 0.37×10-4 m

These are infra-red radiations, and their uses are –

(1) It keeps the Earth warm.

(2) Infra-red lamps are used to treat muscular strains.

3) Write any 2 applications of Infra-red radiations?

The application of infra-red radiations are-

• Infrared radiations are also used in spectroscopy and astronomy.

4) Which component radiation of the electromagnetic spectrum is used to photograph interior organs of the human body and air aircraft navigation?

To photograph internal parts of the Human body X – Rays are used, and microwaves are used for air aircraft navigation.

### 5) Write a few properties of infrared radiation.

Following are a few properties of infrared radiation:

1. Infrared radiation travels at a speed of 299,792,458 meters per second.
2. Infrared radiation increases the thermal energy in particles.
3. Infrared light can exhibit both wave and particle nature at the same time.
4. Infrared radiations can be absorbed or reflected depending on the nature of the material that it strikes.

6) What are Electromagnetic Waves?

When an electric field comes in contact with the magnetic field, electromagnetic waves are produced, and these electromagnetic waves are also known as EM waves. Electromagnetic radiations are composed of electromagnetic waves. We can also say that oscillating electric and magnetic fields are also responsible for the formation of electromagnetic waves.

7) Write any 4 characteristics of EM waves.

• As the EM waves propagate by fluctuating the electric and magnetic fields such that the two fields are perpendicular to each other, this means that the Electromagnetic waves are transverse in nature.
• The reason behind the production of electromagnetic waves is the accelerating charged particle.
• Electromagnetic waves possess a constant velocity nearly equal to 3×108ms−1 in vacuum, and it is denoted by C = 1/√μoϵo. The propagation of electromagnetic waves does not require any material medium to travel.

8) A plane EM wave travels in vacuum along the z-direction. If the frequency of the wave is 40MHz, what can you say about the directions of its electric and magnetic field vectors? Also, what will be its wavelength?

The EM wave travels in the z-direction in vacuum, and the electric field (E) and magnetic fields (M) are in the x y plane, perpendicular to each other.

Frequency of the wave, v = 40MHz = 40×106s−1

Speed of light in a vacuum, c=3×108m/s

Wavelength of a wave is given as: λ=c/v = 3×108/ 40×106 = 7.5m

It is given that, a radio can tune to,

Minimum frequency, ν1 = 8.5 MHz= 8.5 × 106 Hz

Maximum frequency, ν2 = 14 MHz = 14 × 106 Hz

Speed of light, c = 3 × 108 m/s

Corresponding wavelength for ν1 can be calculated as:

λ1= c/ ν1 = 3×108/ 8.5×106 = 35.29m

Corresponding wavelength for ν2 can be calculated as:

λ2= c/ ν2 = 3×108/ 14×106 = 21.42m

Thus, the wavelength band of the radio is 39.5 m to 21.42 m.

### 10) What are the Applications of Electromagnetic Waves?

Few applications of electromagnetic waves are listed below-

• EM radiations are helpful in transmitting energy in vacuum or no medium at all.
• EM waves play a vital role in communication technology.
• EM waves are used in RADARS.
• UV rays are very helpful in detecting fake bank notes.
• Infrared radiations are used in security cameras and are also used for night vision.

### Practice Questions

1. Write down the sequence of propagation of EM waves.
2. Explain what EM waves are and write down their characteristics.
3. What are the applications of EM waves?
4. Why can photons travel at the speed of light while other particles cannot?
5. Explain the formation of EM waves.

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