A point source is placed at the bottom of a ...

CBSE Class 12 Physics 2025 All Sets Solved Paper

Question : 8 of 16

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A point source is placed at the bottom of a tank containing a transparent liquid (refractive index n) to a depth H. The area of the surface of the liquid through which light from the source can emerge out is

$\; \frac{\pi H^2}{n-1}$
$\; \frac{\pi H^2}{n^2-1}$
$\; \frac{\pi H^2}{\sqrt{n^2+1}}$
$\; \frac{\pi H^2}{n^2+1}$

Solution:

For a point source placed at the bottom of a tank, the emergent area through which light escapes depends on total internal reflection and Snell’s Law. The area of the liquid surface through which light emerges is given by:

A = \; \frac{\pi H^2}{n^2-1}

= \; \frac{\pi H^2}{n-1}

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