Monochromatic light falls at an angle of incidence i on a slab of a transparent material (refractive index `mu`). If reflected and refracted rays are mutually perpendicular, find the relation between `mu` and `i`.

Explanation

`i+r=90^@impliesr=90^@-i`
`1xxsini=musinr`
`sin i=musin (90^@-i)`
`=mu cos i`
`tan i =mu`
`i=tan^-1(mu)`