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 of a light wave is a surface on which the phase of the wave is constant. It is a surface where every point on it has the same phase of oscillation.

- In the case of plane waves, the wavefronts are flat and the light rays are parallel to each other.

- For spherical waves, the wavefronts are spherical and radiate outward from a point source.

Refraction of a Plane Wavefront through a Convex Lens:

When a plane wavefront strikes a convex lens, the light rays are refracted (bent) due to the change in speed as they move from one medium to another. The convex lens converges the parallel light rays to a point called the focal point.

Shape of the Refracted Wavefront:

• Before refraction, the wavefront is a straight line (plane wave).
• After passing through the convex lens, the wavefronts bend and become curved.
• The refracted wavefronts now resemble part of a spherical wavefront. The light rays converge towards the focal point of the lens.

The refracted wavefronts are no longer parallel but are bent inward, becoming part of a spherical surface centered at the focal point of the lens.

Final Answer:

The plane wavefront, after passing through the convex lens, becomes curved and converges toward the focal point. The shape of the refracted wavefront is part of a spherical wavefront.