Question

Explain Huygen's construction of spherical wavefront.

Answer 1

Consider a point source of monochromatic light S in a homogeneous medium. The light waves travel with the same speed($v$) in all the directions. After the time ${}^{\prime }{t}^{\prime }$, the waves will reach all the points which are at a distance $vt$ from S. This is the spherical wavefront XY. Let A, B, C be points on the wavefront. To find the new wavefront after a time $\Delta t$, we draw spheres of radius $v\Delta t$ with A, B and C as centres. The tangents drawn to these spheres is the new spherical wavefront.