A beaker containing liquid is placed on a table underneath a microscope with can be moved along a vertical scale. The microscope is focussed, through the liquid into a mark on the table when the reading on the scale is a. It is next focussed on the upper surface of the liquid and the reading be . More the liquid is added and the observations are repeated, the corresponding readings are
and
.The refractive index of the liquid is
The real depth ( R.I. ) apparent depth
In first case, the real depth
Similarly in the second case, the real depth
Since, the difference of real depths
.
Since the liquid is added in second case,