Question

The refractive index of glass, when a ray of light travels from air to glass is 1.5. Calculate the refractive index when light travels from glass to air.

Answer 1

Step 1:

Given⇢ The refractive index of glass when a ray of light travels from air to glass is 1.5.

To find⇢ Determine the refractive index when light travels from glass to air.

According to the Principle of Reversibility of Light, “If a ray of light travels from medium of air to medium of glass along a certain path, it follows exactly the same path while traveling from medium of glass to medium of air”.

In other words, the path of light is reversible.

So, ${}^a\mu _g=\frac{1}{{}^g\mu _a}$

It means that the refractive index of medium of glass with respect to the medium of air is equal to the reciprocal of the refractive index of the medium of air with respect to the medium of glass.

Step 2:

According to the question,

${}^a\mu _g=1.5$

${}^a\mu _g=\frac{1}{{}^g\mu _a}$

$1.5=\frac{1}{{}^g\mu _a}$

${}^g\mu _a=\frac{1}{1.5}$

${}^g\mu _a=0.67$

Step 3:

Therefore, the refractive index when light travels from glass to air, ${}^g\mu _a$ is $0.67$.