Explain plane wave refraction from denser to rarer medium using Huygen's principle.

Explanation

Let speed of light in denser medium is `v_(1)` and in rarer medium is `v_(2)` and `v_(2)gtv_(2)`.
Refracted ray moves away from the perpendicular when it goes from the denser medium to rarer medium.
At certain incident angle, angle of refraction becomes `90^(@)`. This angle is called critical angle `i_(e)`.
From Snell.s law,
`n_(1)sini=n_(2)sinr`
If `i=i_(c),` then `r=90^(@)` hence `sin90^(@)=`
`:.sini_(c)=(n_(2))/(n_(1))`
We will not find any refraction ray for all the angles greater than the critical angle.
Rarer medium for which `v_(2)gtv_(1)` the refraction of incident plane on it refracted away from perpendicular of plane wave. This is shown in figure.