Question

A coin placed at the bottom of a vessel appears to be raised when water is poured in the vessel. Explain.

Answer 1

A coin placed at the bottom of a vessel appears to be raised when water is poured in the vessel due to the phenomenon of refraction.
When the rays of light from the coin travel from denser medium to rarer medium, the refracted rays bend away from the normal.
The point from which the refracted rays appear to come, gives the apparent position of the coin. Since the rays appear to come from a point above the coin, it appears to be raised.