Define a wave-front. Using Huygens’ principle, draw the shape of a refracted wave-front, when a plane wave is incident on a convex lens.
OR

(a) When a wave is propagating from a rarer to a denser medium, which characteristic of the wave does not change and why? (b) What is the ratio of the velocity of the wave in the two media of refractive indices μ₁ and μ₂?

Question

Define a wave-front. Using Huygens’ principle, draw the shape of a refracted wave-front, when a plane wave is incident on a convex lens.
OR

(a) When a wave is propagating from a rarer to a denser medium, which characteristic of the wave does not change and why? (b) What is the ratio of the velocity of the wave in the two media of refractive indices μ₁ and μ₂?

Philoid · Accepted Answer

Huygens’ principle gives the wave front at any time allowing us to determine the shape of the wave-front at a later time. According to Huygens’ construction,

 Every point on a wave front acts as a source for secondary wavelets.

 The secondary wavelets spread in all directions in space (vacuum) with the velocity of light.

The envelope of wave-front of secondary wavelets, after a given time, along forward direction gives the new position of wave-front.

Consider the plane wave ABC incident on a convex lens. Using Huygens’ construction, wave-front emerging out of the lens would be A’B’C’ as shown:

OR

(a) The frequency of a wave stays invariant to change in medium as it is the property of the source.

(b.) Ratio of velocities in the two media,