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. 1.3
C. 1.36
D. 1.42

Answer

C

Explanation

`tan theta =(5.77)/10=0.577`
`implies theta = 30^@`
Further we can apply Snell.s law to find refractive index of the liquid.
`mu sin theta ` = constant
`implies 2.7xxsin 30^@ = mu xx sin 90^@`
`implies mu=(2.72)/2 = 1.36`