Question

Draw a neat labeled diagram of reflection of light from a plane reflecting surface on the basis of wave theory.

Answer 1

Hint: The wave theory corresponds to the Huygens wave principle. Draw a wave front for an incident ray first. After this use Huygens principle and draw the reflected wave front. This shall give the diagram.

Complete answer:
Huygens principle states that-
I)Every point on a wave front is a source of a new wave.
II)The new wave front will be the line tangent to all the wavelets.
III)The wavelets spread in the thrust direction of the source wave.

The laws of reflections are-
I)The incident, reflected and the normal ray are in the same plane.
II)The angle of incidence is equal to the angle of reflection.

Using the Huygens wave principle-
Consider a plane wave incident at an angle i on a reflecting surface XY. The wave front AB will be perpendicular to the incident ray. The ray meets the surface XY at A.
Let the speed of the wave in the medium be v and let t be the time taken by the wave front to reach the point C from B.
Thence, BC = v x t.

To construct the new reflected wave front-
Draw a sphere of radius equal to BC i.e. (v x t) from the point A. Now draw a tangent from point C to the drawn circle. Let the point of contact be D. This way we get the new reflected wave front CD.

Note:
In order to get the point D one can even draw the reflected ray, and then draw a circle of radius equal to BC from point A. The point of intersection of the circle and the reflected ray will be the point D. Join it with C to get the wave front CD. One should note that AD is the reflected ray only.