Question

When the un-polarised light beam is incident from air to glass \((n=1.5)\) at the Brewster's angle,

• A. reflected beam is polarized \(50\ \%\).
• B. reflected and refracted beams are partially polarized.
• C. reflected beam is polarized \(100\ \%\).
• D. refracted beam is polarized \(100\ \%\)

Hint:

At the Brewster angle the reflected and refracted rays are at right angles, and only vibrations perpendicular to the plane of incidence are reflected.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
At the polarising (Brewster) angle \(i_p\), the reflected ray and the refracted ray are perpendicular to each other. The angle satisfies \(\tan i_p = n\).

Step 2: Which Vibrations Are Reflected
Vibrations parallel to the plane of incidence are not reflected at this angle. So the reflected light contains only vibrations perpendicular to the plane of incidence.

Step 3: Degree of Polarisation
The reflected beam is therefore completely plane polarised, that is \(100\ \%\) polarised. The refracted beam still carries some perpendicular vibrations, so it is only partially polarised.

Step 4: Compare the options
Only the option that says the reflected beam is \(100\ \%\) polarised matches this result.

Final Answer:
The reflected beam is 100% plane polarised at the Brewster angle. \[ \boxed{\text{(C) }\text{reflected beam is polarized }100\ \%} \]