Question

Using Huygen's Principle, draw the construction of a propagating circular
wave front.​

Answer 1

Answer:

Now in right-angled triangles ABB' and AA'B'

∠ABB

′

=∠AA

′

B

′

(both are equal to 90

0

)

side BB' = side M' (both are equal to vt)

and side AB' is common. i.e., both triangles are congruent.

∴ ∠BAB

′

=∠AB

′

A

′

i.e., incident wavefront AB and reflected wavefront A'B' make equal angles with the reflecting surface XY. As the rays are always normal to the wavefront, therefore the incident and the reflected rays make equal angles with the normal drawn on the surface XY, i.e.,

Angle of incidence i = Angle of reflection r

This is the second law of reflection.

Since AB, A'B' and XY are all in the plane of paper, therefore the perpendiculars dropped on them will also be in the same plane.

Therefore we conclude that the incident ray, reflected ray and the normal at the point of incidence, all lie in the same plane.

This is the first law of reflection.

Thus Huygen's principle explains both the laws of reflection.