Question

Define ‘wavefront’ of a light wave. A plane wavefront is refracted from a convex lens. Draw the shape of the refracted wavefront.

Hint:

Refraction through a convex lens bends the plane wavefront, causing the wavefronts to converge towards the focal point. This is an example of how lenses focus light.

Answer 1

A wavefront is a surface where a light wave's phase is constant, meaning all points on it oscillate with the same phase.

- Plane waves have flat wavefronts, with parallel light rays.

- Spherical waves have spherical wavefronts originating from a point source.

Refraction of a Plane Wavefront through a Convex Lens:

When a plane wavefront encounters a convex lens, its light rays refract (bend) due to a change in speed between mediums. The convex lens focuses these parallel rays to a focal point.

Shape of the Refracted Wavefront:

• Initially, the wavefront is linear (a plane wave).
• After traversing the convex lens, the wavefronts bend and become curved.
• The refracted wavefronts then approximate part of a spherical wavefront, with rays converging towards the lens's focal point.

The refracted wavefronts are no longer parallel; they bend inward, forming a section of a spherical surface centered at the lens's focal point.

Final Answer:

Upon passing through a convex lens, a plane wavefront becomes curved and converges towards the focal point. The resulting shape of the refracted wavefront is a segment of a spherical wavefront.