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

A wavefront is the surface of constant phase, or the locus of all points having the same phase of vibration. A wavefront can be classified into three types:
1. **Spherical wavefronts**: These are produced by a point source.
2. **Cylindrical wavefronts**: These are produced by a line source.
3. **Plane wavefronts**: These are produced by a distant source.
When a plane wavefront passes through a convex lens, the wavefront gets refracted, and its shape changes. The incident wavefront is parallel, while after refraction, the wavefront becomes converging. The refracted wavefront will be closer to the focal point of the lens, depending on the curvature of the lens. The diagram below illustrates this.

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