Question

When an unpolarized light of intensity I is incident on a polarizing sheet, the intensity of the light which is not transmitted is?
A. ${I_0}/2$
B. ${I_0}/4$
C. $zero$
D. ${I_0}$

Answer 1

Hint: In this question think of the basic phenomena of transmission of unpolarized light (that has oscillations in both the directions) through a polarization filter, after passing through this the oscillations get reduced to single sided only. This will help commenting upon the intensity of the light which is not transmitted.

Complete Step-by-Step solution:
Polarized Light -
Light is formed by a combination of electromagnetic rays. It consists of both the electric and magnetic fields oscillating at 90 Degrees to each other.
The light waves propagate at a perpendicular angle to the oscillations of electric and magnetic fields.
When oscillations take place in a single direction, we call it Polarized light.

Unpolarized Light -
When oscillations take place in a random direction & not in a single one, we call such rays as unpolarized light. For example, Sun rays or rays emitted by a lamp can be defined as unpolarized light.
Unpolarized to polarized light -
An unpolarized light can be converted into polarized light, simply, by passing the rays through the polarization filter.

In polarization filters, organic molecules in the form of long chains are arranged parallel to each other. When an unpolarized light is passed through these filters, the rays which are arranged parallel to these molecules, get absorbed & thus the light rays that come out of the filter have oscillations in one direction only, making them Polarized Light. Now, since the number of rays in polarized light are reduced to half to that of unpolarized light, the answer to this question will be ${I_0}/2$
In other terms, when an unpolarized light is passed through a polarizing sheet, the intensity of the light that is not transferred is half.

Note - The trick to solving these questions lies in knowing that polarizing sheets have chains of organic molecules arranged parallel to each other. Moreover, in an unpolarized light, oscillations of light waves are random in direction. Thus, when an unpolarized light is converted to polarized light, the intensity of light gets reduced.