Question:

Two polaroids are kept crossed to each other. If one of them is rotated an angle $60^{\circ}$, the percentage of incident light now transmitted through the system is

Updated On: Apr 22, 2024
  • 0.1
  • 0.2
  • 0.25
  • 0.125
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The Correct Option is D

Solution and Explanation

Let $I_{0}$ be the intensity of unpolarised light, so the intensity of first polaroid is $\frac{I_{0}}{2}$. On rotating through $60^{\circ}$ the intensity of lioht from second nolaroid is
$I = \left( \frac{I_0}{2} \right) ( \cos \, 60)^2 $
$= \frac{I_0}{2} \frac{1}{4} = \frac{I_0}{8} = 0.125 I_0$
So, percentage of incident light transmitted through the system is $12.5\%$.
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Concepts Used:

Polarisation

Light travels in form of transverse EM waves. The underlying oscillation is along directions perpendicular to the propagation direction, in this example, oscillating electric and magnetic fields. Process of restricting the vibration of light waves to one direction is known as Polarisation.

Types of Polarisation:

There are three types of polarisation such as:

  1. Linear Polarisation in the electric field of light is limited to one single plane that is along the direction of propagation.
  2. Elliptical Polarisation: In this, both the phase difference and amplitude between the two linear components are not equal.
  3. Circular Polarisation: The electric field of light follows a circular propagation. The two linear components that exist in the electric field are the same amplitudes but have different phase differences.

Methods of Polarisation of Light:

The few methods of polarisation of Light are:

  • Polarization by dispersing
  • Polarization by Reflection
  • Polarization by Refraction
  • Polarization By Transfer