Question:
A jar of height h is filled with a transparent liquid of refractive index µ. At the centre of the jar on the bottom surface is a dot. Find the minimum diameter of a disc, such that when placed on the top surface symmetrically about the centre, the dot is invisible.
Solution:
tan ic d/2/h
ic = d/2h
d = 2h tan ic
d = 2h ×1/√μ2 – 1