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

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

$\;{π H^2}/{(n-1)}$
$\;{π H^2}/{(n^2-1)}$
$\;{π H^2}/{{√{n^2+1}}}$
$\;{π H^2}/{(n^2 +1)}$

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 = \;{ π H^2 }/{(n^2-1)}

= \;{π H^2}/{(n-1)}

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