$A$ point source of light is placed at the focus of a concave mirror. Consider only paraxial rays. The shapes of the wavefronts of incident and reflected lights respectively are

Huygens' principle is applicable to

Which of the following is correct for light diverging from a point source?

$A$ plane wavefront is incident on a water surface at an angle of incidence $60^{\circ}$. It then gets refracted at an angle of $45^{\circ}$. The ratio of the width of the incident wavefront to that of the refracted wavefront is $\left[\sin \frac{\pi}{4}=\cos \frac{\pi}{4}=\frac{1}{\sqrt{2}}, \sin 60^{\circ}=\frac{\sqrt{3}}{2}, \cos 60^{\circ}=\frac{1}{2}\right]$

When a point source of light is placed at the focus of a convex lens,light emerges from the lens. What is the shape of the wavefront of the emerging light?

$A$ 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: