Question

Which of the following cannot be polarised?
(A) Radio waves
(B) $\beta$ rays
(C) Infrared rays
(D) $\gamma$ rays

Answer 1

Hint The term ‘Polarisation’ of a wave can be defined as the vibration of the wave in only one direction, i.e., perpendicular to the direction of propagation of the wave. All types of electromagnetic waves can be polarised easily.

Complete step-by-step answer:
All the transverse waves like electromagnetic waves can be polarised while the longitudinal waves cannot be polarised because the motion of the wave particles is already in one direction, i.e., the direction of propagation of the wave.

1. Radio waves
The radio waves are a part of the electromagnetic spectrum.
In other words, radio waves are electromagnetic waves.
So they are transverse waves.
Hence, they can be polarised.

2. $\beta$ rays
The $\beta$ rays are not a part of the electromagnetic spectrum.
In fact, they are considered as a stream of electrons.
So they are a type of longitudinal waves.
Hence, they cannot be polarised as they are unidirectional.

3. Infrared Rays
The infrared waves are also a part of the electromagnetic spectrum.
In other words, these rays are also electromagnetic waves.
So they fall under the category of transverse waves.
Hence, they can be polarised.

4. $\gamma$ Rays
The $\gamma$ rays are also a part of the electromagnetic spectrum.
In other words, $\gamma$ rays are high energy electromagnetic waves.
So they also come under the category of transverse waves.
Hence, they can also be polarised.

The correct answer is (B) $\beta$ rays.

Note $\beta$ rays are often confused with electromagnetic waves. They do not fall under the electromagnetic spectrum. In reality, these rays are just a stream of electrons. They are negative in nature. As they are longitudinal waves, they cannot be polarised.