A point source S is placed at the bottom of a tranparent block of height 10mm and refractive index 2.72. It is immersed in a lower refractive index liquid as shown in the figure. It is found that the light emerging from the block to the liquid forms a circular bright spot of diameter 11.54 mm on the top of the block. The refractive index of the liquid is `

Options

A. `1.21`
B. `1.30`
C. `1.36`
D. `1.42`

Answer

C

Explanation

If `theta` is critical angle between the pair of media in contact, then from Fig.
`tan theta = (11.54//2)/(10) = 0.577`
`:. theta = 30^@`
Now `.^1 mu_2 = (1)/(sin theta) = (2.72)/(mu) = (1)/(sin 30^@) = 2`
`2 mu = 2.72, mu = 1.36`.
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