A light passes through many parallel slans one by one as shown in figure.

Prove that `n_(1) sin i_(1) = n_(2) sin i_(3) sin = n_(4) sin i_(4) = .....` [Remember this]. Also prove that if `n_(1) = n_(2)` then light rays in medium `n_(1)` and in medium `n_(4)` are parallel.

Explanation

We have,
` (sin i_(1))/(sin i_(2)) = (n_(2))/(n_(1))`
`rARr n_(1) sin i_(1) = n_(2) sin i_(2)....(i)`
Similarly `n_(2) sin i_(2) = n_(3) sin i_(3)`
So on
So, `n_(1) sin i_(1) = n_(2) sin i_(2) = n_(3) sin i_(3) = ...........`
`n_(1) sin i_(1) = n_(4) sin i_(4) rArr sin i_(1) = sin i_(4) ( :. n_(1) = n_(2))`
so, `i_(1) = i_(4)`
Hence lights rays in medium `n_(1)` and in medium `n_(4)` are parallel.