Question

If a monochromatic beam of light undergoes minimum deviation through an equi angular prism, how does the beam pass through the prism, with respect to its base?

• A. parallel to the base
• B. not parallel to base
• C. both A & B
• D. cant say

Answer 1

The correct option is A parallel to the base

For minimum deviation the angle of refraction $r=\frac{A}{2}$. For an equiangular prism $A={60}^0$ and hence, $r=\frac{60}{2}={30}^o$. Thus,if the angle it makes with the normal is ${30}^o$, the ray will make an angle of ${60}^o$ with both the surfaces of the prism. Hence, it is parallel to the base which also makes angles of ${60}^o$ with both the surfaces.