## Question

Glycerine (refractive index 1.4) is poured into a large jar of radius 0.2 m to a depth of 0.1 m. There is a small light source at the centre of the bottom of the jar. Find the area of the surface of glycerine through which the light passes.

### Solution

0.0327 m^{2}

Let *S* be the light source. If light falls on the surface at critical angle *c*, it grazes along the surface, as shown. Now,

from the figure, we have

The area of the surface through which light passes is

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_{a}n_{w}