Question 1

What does a Polaroid do to unpolarised light?

Accepted Answer

An ideal Polaroid passes only the electric-field component along its principal transmission axis. Unpolarised light contains transverse E-components in many directions, so the emerging light vibrates along one definite transverse axis and is plane-polarised.

Question 2

What is Brewster's law?

Accepted Answer

For light travelling from a medium of refractive index n1 into another medium of index n2, Brewster's law is tan theta_B = n2 / n1. For air to glass with n approximately 1.5, the Brewster angle is about 56.3 degrees.

Question 3

What happens to reflected and refracted light at Brewster's angle?

Accepted Answer

The reflected and refracted rays meet at 90 degrees. The reflected beam is completely plane-polarised with its E-field perpendicular to the plane of incidence, while the refracted or transmitted beam remains only partially polarised.

Question 4

How does optional enrichment Malus law describe a rotating analyser?

Accepted Answer

This optional enrichment is not required NCERT content. For already-polarised light of intensity I(P1), an analyser at angle theta transmits I = I(P1) cos²theta. Transmission is full at 0 degrees, half at 45 degrees, and zero at 90 degrees.

Question 5

Why can the reflected beam be extinguished but the transmitted beam cannot?

Accepted Answer

At Brewster's angle the reflected beam is completely polarised, so a properly crossed analyser blocks all of its E-field component. An ideal analyser’s transmitted output is plane-polarised along its transmission axis. For the partially polarised refracted beam, the transmitted intensity remains nonzero, but the output is still plane-polarised.

Polarisation Lab — Brewster Angle & Optional Malus Law

About this lab

Practice