Question

A light ray is travelling from denser to rarer medium. The angle of incidence is equal to the critical angle. Then which of the following statements is/are true?

• A. The angle of refraction is 90 degrees.
• B. The refracted ray passes along the boundary separating the two medium.
• C. The incident ray bounces back to the denser medium.
• D. The incident ray passes undeviated from denser medium to rarer medium.

Answer 1

Answer: (A), (B)

The correct options are
A The angle of refraction is 90 degrees.
B The refracted ray passes along the boundary separating the two medium.

The critical angle is the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is 90 degrees. When the angle of incidence in the denser medium is equal to the critical angle, then the refracted ray passes along the boundary separating the two medium.
If the angle of incidence is greater than the critical angle, the ray will be reflected back to the same medium without undergoing refraction. This is known as total internal reflection.