Consider the situation shown in figure. Light from a point source S is made parallel by a convex lens L. The beam travels horizontally and falls on an `88^@-88^@-4^@` prism as shown in figure. It passes through the prism symmetrically. The transmitted light falls on a vertical mirror. Through what angle should the mirror be rotated so that an image of S is formed as S itself?

Explanation

The parallel beam after going through the prism will be deviated by an angle `delta`. If the mirror is also rotated by this angle `delta`. The rays will fal normally on it. The rays will be reflected back along the same path and form the image of S on itself.
as the prismis thin, the angle `delta` is given by
`delta=(mu-1)A`
`=(1.5-10xx4^@=2^@`
thus , the mirror should be rotated by `2^@`