Question

Write Huygens' principle of secondary wavelets and explain the laws of refraction of light on its basis.

Hint:

Remember that Huygens' principle works well in explaining wave behaviors such as refraction, diffraction, and interference.

Answer 1

Huygens' principle states that every point on a wavefront is a source of secondary wavelets that spread out in the forward direction at the same speed as the original wave. The new wavefront at any time is the envelope of all these secondary wavelets.
For the laws of refraction:
- The incident ray, the refracted ray, and the normal to the surface at the point of incidence all lie in the same plane.
- The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant and is equal to the refractive index of the medium, i.e., \(\sin i / \sin r = \mu\).