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Asked in GUJCET 2025 · Wavefronts and Huygens construction
Given: light diverging from a point source in a homogeneous medium.
Idea: a wavefront is the surface over which the disturbance has the same phase at one instant, so its shape follows from how far the wave has gone in each direction.
In a homogeneous medium the speed is the same in every direction, so after a time t every point at the distance r = vt from the source is in step.
The set of points at one fixed distance from a point is a sphere, so the wavefronts are concentric spheres expanding outwards.
Their intensity falls as 1/(r²), because the same power is spread over the growing area 4π r².
So for light diverging from a point source the wavefront is spherical.
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