Question

Define a wavefront. An incident plane wave falls on a convex lens and gets refracted through it. Draw a diagram to show the incident and re fracted wavefront.

Hint:

Wavefronts represent the phase surfaces of a wave, and the shape of the wavefront changes depending on the medium or the lens used to refract the wave.

Answer 1

Wavefronts and Refraction through a Convex Lens 

A wavefront is the surface of constant phase, or the locus of all points having the same phase of vibration. There are three main types of wavefronts:

• Spherical wavefronts: Produced by a point source.
• Cylindrical wavefronts: Produced by a line source.
• Plane wavefronts: Produced by a distant source.

Refraction of a Plane Wavefront through a Convex Lens:

When a plane wavefront passes through a convex lens, the wavefront gets refracted, and its shape changes. Here is how it behaves:

• The incident wavefront is parallel (straight) to the axis of the lens.
• After refraction, the wavefront becomes converging and starts to focus towards the focal point of the lens.
• The refracted wavefront gets closer to the focal point depending on the curvature of the lens.

The diagram below illustrates the process:

Conclusion:

The incident wavefront is straight and parallel to the axis, while after passing through the convex lens, the refracted wavefront converges towards the focal point of the lens.