Write laws of refraction. Explain the same with the help of ray diagram, when a ray of light passes through a rectangular glass slab.

Explanation

Refraction of light occurs according to certain laws called the Snell.s laws of refraction.
Law 1 : The incident ray, the refracted ray and the normal at the point of incident, at the interface of the two transparent media, all lie in the same plane.
Law 2 : The ratio of sine of angle of incidence (sin i) to the sine of angle of refraction (sin r) is a constant, for the light of a given colour and for the given pair of media. This is true for angle `0^(@)lt i lt 90^(@)`.
`(sin i)/(sin r)` = constant `= mu`
This constant value `(mu)` is called the refractive index of the second medium with respect to the first.

Explanation :
(i) When the light ray (incident ray AE), travels from air to glass (rarer to denser medium) ,
• The refracted ray EF bends towards the normal `N_(1) N_(2)`.
• Angle of incidence `angle AEN_(1) gt` Angle of refraction `angle N_(2)EF`
(ii) When the light ray EF travels inside the glass slab :
The ray EF travels in a straight line. There is no refraction as there is no change in media here.
• The ray EF strikes the surface SR of the slab at F
• `angle N_(2)EF = angle EFN_(1)`. [Consider `N_(2)N_(1)` and `N_(2).N_(1).` as two parallel lines and EF as the transversal, Interior alternate angles are equal].
(iii) When the incident light ray EF travels from glass to air, (denser to rarer medium),
• The refracted ray FD bends away from the normal `N_(1). N_(2).`.
• The refracted ray FD is also called emergent ray as it is emerging out of the glass slab.
• Angle of incidence `angle EFN_(1). angle` Angle of refraction `angle N_(2).FD` as the light ray is moving from rarer to denser medium.
(iv) if there was no glass slab, the ray AE would have continued in the direction shown by the dotted line, which is the original path of the light ray in the absence of the second medium.
(v) The light ray FD emerging out of the glass slab is at a distance of .d. from the dotted line AE. .d. is called as lateral displacement or leteral shift.