CBSE Class 12-science Answered

As electromagnetic waves, and in this case, radio signals travel, they interact with objects and the media in which they travel. As they do this the radio signals can be reflected, refracted or diffracted. These interactions cause the radio signals to change direction, and to reach areas which would not be possible if the radio signals travelled in a direct line.

Polarisation

The polarisation of an electromagnetic wave indicates the plane in which it is vibrating. As electromagnetic waves consist of an electric and a magnetic field vibrating at right angles to each other it is necessary to adopt a convention to determine the polarisation of the signal. For this purpose the plane of the electric field is used.

Reflection

Reflection of light is an everyday occurrence. Mirrors are commonplace and can be seen in houses and many other places. Shop windows also provide another illustration for this phenomenon, as do many other areas. Radio waves are similarly reflected by many surfaces.

Refraction

It is also possible for radio waves to be refracted. The concept of light waves being refracted is very familiar, especially as it can be easily demonstrated by placing a part of stick or pole in water and leaving the remaining section in air. It is possible to see the apparent change or bend as the stick enters the water.

Diffraction

Radio signals may also undergo diffraction. It is found that when signals encounter an obstacle they tend to travel around them. This can mean that a signal may be received from a transmitter even though it may be "shaded" by a large object between them. This is particularly noticeable on some long wave broadcast transmissions