Question

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

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

Answer 1

Answer: (D)

1cm downward

Answer 2

: In the later case microscope will be focused for O’

So,it is required to be lifted by distance OO’. OO’ = real depth of O – apparent depth of O

$= 3 - \frac{3}{1.5}\left\lbrack \mu = \frac{realdepth(okLrfodxgjkbZ)}{apparentdepth(vkHkklhxgjkbZ)} \right\rbrack$

$= 3\left\lbrack \frac{1.5 - 1}{1.5} \right\rbrack = \frac{3 \times 0.5}{1.5} = 1cm$ (up ward)