$A$ plane wavefront travelling in a straight line in vacuum encounters a medium of refractive index $\mu$. At point $P,$ the shape of the wavefront is:

Initially,parallel cylindrical wavefronts travel 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. The intensity decreases as the radius increases. What happens when it enters the second medium?

Explain the wavefront and its types.

For light diverging from a point source,

The wavefront of a distant source of unknown shape is approximately

$A$ plane wavefront of width $x$ is incident on an air-water interface, and the corresponding refracted wavefront has a width $y$. The refractive index of air with respect to water in terms of distances $w$ and $z$ is: