A ray of light is incident at angle of incident ,I, on one face of a prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is `mu` the angle of incidence i, is nearly equal to:

Explanation

For face AB, ` angle i =0^@ , therefore angle r = 0^@` the ray will pass through AB undeflected
Now, at face AC

Formula : Here ` i_c = sin^(-1) (1/mu)`
` = sin^(-1) (2/3) = sin^(-1) (0.66)`
`angle i` on face AC is `30^@` which is less than `anglei_c` . Hence, the ray get refracted. And, applying Snell's law at face A
` sin 30^@ xx 3/2 = sin r xx 1`
`rArr sin r = 1/2 xx 3/2 `
` rArr r = sin^(-1) (3/4) = sin^(-1) (0.75)`
And, clearly r > i, as ray passes from clenser to rarer medium.