Huygens Principle

State Huygen’s principle.

Figure shows a standard two slit arrangement with slits S₁, S₂, P₁, P₂ are the two minima points on either side of P (Figure). At P₂ on the screen, there is a hole and behind P₂ is a second 2-slit arrangement with slits S₃, S₄ and a second screen behind them.

Define the term wavefront. Using Huygen’s wave theory, verify the law of reflection. 

Consider a plane wave front incident on a thin convex lens. Draw a proper diagram to show how the incident wave front traverses through the lens and after refraction focusses on the focal point of the lens, giving the shape of the emergent wave front.

A plane wave front AB propagating from denser medium (1) into a rarer medium (2) is incident on the surface P₁P₂ separating the two media as shown in fig.

Using Huygen’s principle, draw the secondary wavelets and obtain the refracted wave front in the diagram.

According to Huygens’s principle, the amplitude of secondary wavelets is ______.

What is the shape of the wavefront in the following case?

The portion of the wavefront of light from a distant star was intercepted by the Earth.

What is the geometrical shape of the wavefront for:

1. Light diverging from a point source?
2. The pattern of wavefront of the light from a distant star intercepted by earth?