The wavefront of a distant source of unknown shape is approximately

$A$ parallel cylindrical beam of light propagates in a medium with a refractive index $\mu(I) = \mu_0 + \mu_2 I$,where $\mu_0$ and $\mu_2$ are positive constants and $I$ is the intensity. As the intensity of the light decreases,the radius increases. The initial shape of the wavefront is:

State and explain Huygens' principle.

$A$ wavefront is a surface

What is the most important point of Huygens' wave theory?

On a hot summer night,the refractive index of air is smallest near the ground and increases with height from the ground. When a light beam is directed horizontally,the Huygens' principle leads us to conclude that as it travels,the light beam