If the angle of incidence and angle of emergence of a light ray falling on a glass slab are i and e respectively, then prove that i=e.

Explanation

i. In the above figure,
i = angle of incidence,
r = angle of refraction,
e = angle of emergence.
At point N, using Snell's law,
`""_("glass")n_("air")=(sin i)/(sin r)" ….(1)"`
At point M, using Snell's law,
`""_("air")n_("glass")=(sin r)/(sin e)" ......(2)"`
But `""_("glass")n_("air")=(1)/(""_("air")n_("glass"))`
`therefore" "(sin i)/(sin r)=(1)/((sin r)/(sin e))" "`....[From (1) and (2)]
`therefore" "(sin i)/(sin r)=(sin e)/(sin r)`
`therefore" "sin i= sin e`
`therefore" "angle i = angle e`
ii. Hence, for the refraction of light through a glass slab angle of incidence is equal to angle of emergence, i.e., i=e.