Question

A beam of circularly polarized light is completely absorbed by an object on which it falls. If $U$ represents absorbed energy and $\omega $ represents angular frequency, then angular momentum transferred to the object is given by :
(A) $\dfrac{U}{{{\omega ^2}}}$
(B) $\dfrac{U}{{2\omega }}$
(C) $\dfrac{U}{\omega }$
(D) $\dfrac{{2U}}{\omega }$

Answer 1

Hint: Circularly polarized light has displacement vectors which rotate in the plane perpendicular to the direction of angular velocity. Angular momentum is the ratio of energy and angular velocity.

Complete step by step answer:
Circularly polarized light is the light whose electric or displacement vector rotates in a plane perpendicular to the propagation direction with constant angular velocity.
It is given in the question that,
$U$ is the energy absorbed
$\omega $ is angular frequency
We know that,
Angular momentum due to circular polarized light is given by the ratio of energy absorbed to the angular frequency.
Thus angular momentum $ = \dfrac{U}{\omega }$

Therefore, from the above explanation, the correct answer is, option (C) $ = \dfrac{U}{\omega }$.

Additional information:
Depending on the orientation of the electric field, polarization is classified into three types.
1. Linear polarization: In this type, the electric field of light is restricted to a single plan along the direction of propagation.
2. Circular polarization: In this type, an electric or displacement vector rotates in a plane perpendicular to the propagation direction with constant angular velocity.
3. Elliptical polarization: In this type, the electric field of light describes an ellipse.

Note:This question can be solved if you know the definition and concept of angular momentum. Once, that is known, this question is very easy. This question is a good example to understand how easy a solution can become if we have clear understanding over concepts.