Question

A point source S is placed at the bottom of a transparent block of height 10 mm 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 ______.

विकल्प

• 1.21

• 1.30

• 1.36

• 1.42

Answer 1

A point source S is placed at the bottom of a transparent block of height 10 mm 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 1.36.

Explanation:

Only if the point source's light rays can refract at the surface and emerge from it will they be visible from outside. This only occurs when the source's angle of incidence is below the critical angle and when viewed from a critical angle, Snell's law applies.

2.72 sinα = μ × sin 90°

< br / > `(2.72xx5.77)/11.54` = μ < br / >

< br / > μ = 1.36 < br / >

refractive index of outer region is 1.36.