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A microscope is focused on a mark on a p...

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 ?

A

`4.5 cm` downward

B

`1 cm` downward

C

`2 cm` downward

D

`1 cm` upward

Text Solution

Verified by Experts

The correct Answer is:
D
In the later case mircoscope 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 - (3)/(1.5) [mu = ("real depth")/("apparent depth")]`
`= 3 [(1.5-1)/(30)] = (3 xx 0.5)/(1.5) = 1 cm` (upward)
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