Question

-When a ray of light travels from optically denser medium to optically rarer medium, it always bends ______ the normal
1- towards
2- away from
3- same as
4- cannot say

Answer 1

The propagation of waves depends upon the medium and so waves have different speeds in different mediums. When the medium changes then there is a change in the speed of the wave, so, there must be some change in its direction.

Complete answer:
The categorization of different mediums is done with respect to some medium and we take that medium as air. The refractive index of the air is taken to be unity, the mediums which have refractive index greater than 1 are called denser mediums and the medium which has refractive index lesser than 1 are called rarer medium.
As per Snell’s law when a ray of light travels from a rarer medium to a denser medium, then it bends towards the normal and when the light travels from a denser medium to a rarer medium, it bends away from the normal.

So, the correct answer is “Option 2”.

Note: From Snell’s law, $\mu =\dfrac{\sin i}{\sin r}$
Here I and r are the angles of incidence and refraction respectively. If the RHS is unity, then a ray of light will pass undeflected.
For total internal reflection to take place two conditions must be satisfied. These are;
1-The light ray moves from a denser medium to less dense medium.
2-The angle of incidence must be greater than the critical angle