Practice portal › Wave Optics › Huygens Principle and Wavefronts
Asked in GUJCET 2017 · Wavefronts and Huygens construction
Given: a point source, observed at a very large distance from it.
Idea: a wavefront is the surface joining all the points that are in the same phase; for a point source it is a sphere centred on the source.
The curvature of a sphere of radius r is 1/r, which falls as the wave spreads.
Over the small patch of that sphere which a distant observer intercepts, the curvature is negligible.
So the wavefront is plane -- this is why sunlight arriving at the Earth is treated as a plane wave.
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