Question

A light ray enters from medium A to medium B as shown in the figure. The refractive index of medium B relative to A will be :

• A. greater than unity
• B. less than unity
• C. equal to unity
• D. zero

Answer 1

The correct option is A greater than unity

Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray towards the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media.
Refractive index is the measure of the bending of a ray of light as it passes from one medium to another.
In this case, since ray of light bends towards the normal, when it goes from medium A to medium B, the medium A is rarer and medium B is denser medium. Speed of light in rarer medium ($v_1$) is greater than the speed of light in denser medium ($v_2$) i..e $v_1>v_2$
Thus refractive index of B relative to A $n=\frac{v_1}{v_2}$.

$⟹$ $n>1$