Question

A boy holds a laser pointer at the bottom of a pond and the light ray makes an angle to the surface

i) 35° ii) 40° iii) 49°.

In which case the light ray does not cross the surface of water ? Why?​

Answer 1

The case in which the light ray does not cross the surface of the water will be:

iii) 49°

• This phenomenon in which the light after complete reflection comes back into the medium is known as Total Internal Reflection.

• In this case, the angle of incidence is greater than a certain limiting angle, called the critical angle.

• For the water-air media, the critical angle is around 48.5°.

• Thus looking at the approximate value, the light ray does not cross the surface of the water at 49° in the given experiment.