Question

In the propagation of light waves, the angle between the plane of vibrations and plane of polarisation is :
$\text{A}\text{. }{{0}^{\circ }}$
$\text{B}\text{. 9}{{\text{0}}^{\circ }}$
$\text{C}\text{. 4}{{\text{5}}^{\circ }}$
$\text{D}\text{. 8}{{0}^{\circ }}$

Answer 1

Hint: Light is a transverse wave. It consists of oscillating electric fields and magnetic fields perpendicular to each other. When the light has multiple planes of oscillations, it is called unpolarised light. When it has a single plane of oscillations is called polarised. The plane that has no vibrations is called a plane of polarisations. The plane of vibrations and the plane of polarisation are perpendicular to each other.

Complete answer:
Light is an electromagnetic wave emitted by the sun. An electromagnetic wave is a transverse wave and consists of oscillations of electric and magnetic fields perpendicular to propagation of the wave.
In light, the vibrations are of electric and magnetic fields. Here, the pane of vibrations in electric (oscillating electric field) is perpendicular to the direction of propagation of the light wave. Therefore, light is a transverse wave.

The plane of vibrations of electric fields may be in all the directions. When this plane is not in a specific direction, the light is called unpolarised light.

When the plane of vibrations of an electric field is in a specific direction, the light is called polarised light.
The unpolarised light can be polarised by passing the light through a device called polariser. When the unpolarised light comes out of the polariser, it has only one plane of vibrations. The plane that has no vibrations is called a plane of polarisations.

The plane of vibrations and the plane of polarisation are perpendicular to each other. Hence, the angle between the plane of vibrations and the plane of polarisation is $\text{9}{{\text{0}}^{\circ }}$.

So, the correct answer is “Option B”.

Note:
Let us note one point regarding the intensity of the unpolarised light when it is polarised. When the unpolarised light is polarised, its planes of vibrations become less. Therefore, the intensity of the light reduces when it is polarised.