A microscope is focused on a mark on a piece of paper and then a slab of glass of thickness `3cm` and refractive index `1.5` is placed over the mark. How should the microscope be moved to get the mark in focus again ?

Options

A. 1 cm upward
B. 4.5 cm downward
C. 1 cm downward
D. 2 cm upward

Answer

A

Explanation

Apparent depth of mark as seen through a glass slab of thickness `x` and refractive index `mu` is
Apparent depth `= ("Real detph")/("Refractive index")`
or `x'=(x)/(mu)=N =2 cm`
As image appears to be raised by `1 cm`, thereforem microscope must be moved upward by `1 cm`.