Question

When a beam of unpolarised monochromatic light is incident on a plane glass plate at a polarising angle, which one of the following statements is correct?

• A. Reflected and refracted rays are completely polarised with their planes of polarisation perpendicular to each other.
• B. Reflected light is partially polarised but refracted light is plane polarised.
• C. Reflected and refracted rays are completely polarised with their planes of polarisation parallel to each other.
• D. Reflected light is plane polarised but transmitted light is partially polarised.

Hint:

At Brewster angle, reflected light is fully polarised but refracted light is never completely polarised.

Answer 1

The Correct Option is D

Step 1: Recall Brewster’s law.
At the polarising (Brewster) angle, the reflected light becomes completely plane polarised.

Step 2: Behaviour of refracted (transmitted) light.
The refracted ray still contains vibrations in more than one direction, hence it is only partially polarised.

Step 3: Eliminate incorrect options.
- Complete polarisation of refracted light does not occur.
- Planes of polarisation are not both completely polarised.

Step 4: Conclusion.
Thus, reflected light is plane polarised while transmitted light is partially polarised.