NCERT Solutions for Class 12 Physics Chapter 8 Electromagnetic Waves

The speed of light (3 × 108 m/s) in a vacuum is the same for all wavelengths. It is independent of the wavelength in the vacuum.

The frequency of an electromagnetic wave produced by the oscillator is the same as that of a charged particle oscillating about its mean position i.e., 109 Hz.

Amplitude of magnetic field of an electromagnetic wave in a vacuum, B₀ = 510 nT = 510 × 10⁻⁹ T Speed of light in a vacuum, c = 3 × 10⁸ m/s Amplitude of electric field of the electromagnetic wave is given by the relation, E = cB₀ = 3 × 10⁸ × 510 × 10⁻⁹ = 153 N/C Therefore, the electric field part of the wave is 153 N/C.

From the given electric field vector, it can be inferred that the electric field is directed along the negative x direction. Hence, the direction of motion is along the negative y direction i.e. -j ̂.

Radio waves; it belongs to the short wavelength end of the electromagnetic spectrum.

Long distance radio broadcasts use shortwave bands because only these bands can be refracted by the ionosphere.

It is necessary to use satellites for long distance TV transmissions because television signals are of high frequencies and high energies. Thus, these signals are not reflected by the ionosphere. Hence, satellites are helpful in reflecting TV signals. Also, they help in long distance TV transmissions.

With reference to X-ray astronomy, X-rays are absorbed by the atmosphere. However, visible and radio waves can penetrate it. Hence, optical and radio telescopes are built on the ground, while X-ray astronomy is possible only with the help of satellites orbiting the Earth. (d) The small ozone layer on the top of the atmosphere is crucial for human survival because it absorbs harmful ultraviolet radiations present in sunlight and prevents it from reaching the Earth’s surface.

In the absence of an atmosphere, there would be no greenhouse effect on the surface of the Earth. As a result, the temperature of the Earth would decrease rapidly, making it chilly and difficult for human survival.

A global nuclear war on the surface of the Earth would have disastrous consequences. Post-nuclear war, the Earth will experience severe winter as the war will produce clouds of smoke that would cover maximum parts of the sky, thereby preventing solar light form reaching the atmosphere. Also, it will lead to the depletion of the ozone layer.