Huygens’ Principle applies to spherical waves by treating every point on the surface of a spherical wavefront as a source of secondary wavelets that spread out in all directions.
Here’s how it works:
- A spherical wave originates from a point source, like ripples from a pebble dropped in water.
- According to Huygens’ Principle, at any given moment, every point on the spherical wavefront emits tiny secondary spherical waves.
- These secondary waves travel outward at the same speed in all directions within the medium.
- The new wavefront at a later time is formed by drawing a smooth surface that envelops all the secondary wavelets—this surface is another, larger spherical wavefront.
This continuous process explains how spherical waves propagate outward from a point source. The curvature of the wavefront decreases as it expands, and at large distances, a spherical wavefront can even begin to resemble a plane wave due to the vast radius.
Thus, Huygens’ Principle shows how spherical wavefronts evolve over time, making it a powerful tool in understanding natural wave propagation from point sources.