Question

Use Huygen's principle to show how a plane wavelength propagates from a denser to rarer medium. Hence verify $Snel{l}^{\prime }s$ $law$ of refraction

Answer 1

Huygens's Principle states that every point on a wavefront is a source of wavelets, which spread forward at the same speed.

The new position of the wave front at any instant is the envelope of the secondary wavelets at that instant.

When light is emitted from a source, then the particles around it begins to vibrate and all such particles which are vibrating in the same phase is termed as a wavefront.

Suppose when disturbance from point P on incident wavefront reaches point P on the refracted wavefront, the disturbance from point Q reaches the point Q’ on the refracting surface.

The time taken by light to travel from a point on incident wavefront to the corresponding point on refracted wavefront should always be same.

The index of refraction is the ratio of the speed of light in vacuum, c, to the speed of light in a particular medium, v. That means

$n=\frac{c}{v}$