Question

A thin isosceles prism with angle $4^{\circ }$ and refractive index $1.5$ is placed inside a transparent tube with water $(\text{refractive index}=\frac{5}{4})$ as shown. The deviation of light due to prism will be

• A. ${0.8}^{\circ }\text{upward}$
• B. ${0.8}^{\circ }\text{downward}$
• C. ${0.67}^{\circ }\text{upward}$
• D. ${0.67}^{\circ }\text{downward}$

Answer 1

The correct option is B ${0.8}^{\circ }\text{downward}$

The deviation of light is surely downwards as the light rays pass through the prism plus water system.

For a small angle prism, the light deviation is not much, and the angle of deviation is given by,
$\delta =(\frac{{\mu }_2}{{\mu }_1}-1)A=(\frac{1.5}{\frac{5}{4}}-1)\times 4^{\circ }\delta ={0.8}^{\circ }\text{downward}$