Question

Two beams of red and violet colours are made to pass separately through a prism $($angle of prism is ${60}^{\circ })$. In the position of minimum deviation, the angle of refraction will be :

• A. ${30}^{\circ }$ for both the colours.
• B. greater for the violet colour.
• C. greater for the red colour.
• D. equal but not equal to ${30}^{\circ }$ for both the colours.

Answer 1

The correct option is A ${30}^{\circ }$ for both the colours.

For minimum deviation, the ray in the prism is parallel to the base of the prism. This condition does not depends on the colour of incident rays.
So, in both the cases, angle of refraction will be equal and is given by :
$r=\frac{A}{2}=\frac{{60}^{\circ }}{2}={30}^{\circ }$