Question

What can you say about the angle of deviation in such a situation ?

• A. Angle of deviation is minimum.
• B. Angle of deviation is maximum.
• C. Angle of deviation is constant.
• D. None of the above

Answer 1

The correct option is A Angle of deviation is minimum.

When the ray travels parallel to the base it will be making an angle of ${30}^o$ with the normal at both the surfaces since it is an equilateral prism i.e. angle of prism $A$ is ${60}^o$. This implies that the angle of refraction $r$ is ${30}^o$. For minimum deviation $r=A/2$ which is satisfied in this case.