A mark is made on the bottom of beaker and a microscope is focussed on it. The microscope is raised through `1.5 cm`. To what height water must be poured into the beaker to bring the mark again into focus ? Given that `mu` for water is `4//3`.

Answer

`6 cm`

Explanation

Here, apparent shift,
`d = 1.5 cm`
Let `t` be the height which water must be poured into the beaker.
As `d = t (1 - (1)/(mu))`
`:. 1.5 = t (1 - (1)/(4//3)) = (t)/(4) , t = 4 xx 1.5 = 6 cm`