A point source of light is placed at the bottom of a tank containing a liquid $(R.I= \mu)$ upto a depth $h$. A bright circular spot is seen on the surface of the liquid. Then the radius of this bright spot.:

Question

$(a)\;-h \\ (b)\;\frac{h}{\mu} \\ (c)\;\frac{h}{\sqrt {\mu-1}} \\ (d)\;\frac{h}{\sqrt{\mu^2-1}}$