What is the reason behind the disturbing of incoming and reflected signals when a low flying aircraft passes overhead, which results in slight shaking of the picture on our TV screen?

Assertion: A spherical wavefront is produced by a point source of light.

Reason: It is because, the locus of all points, which are equidistant from the point source, is a sphere.

Except for polished surfaces, ${\tan }^{-1}\left(\mathrm{\mu }\right)$ in Brewster's law depends upon which of the following?