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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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Knowledge Check

  • The time taken by a ray of light to travel through a glass slab of thickness 2 cm and refractive index 1.5 will be

    A
    `10^(-8) s
    B
    `10 ^(-10) s`
    C
    `2 xx 10^(-8) s`
    D
    `10^(-12) s`

  • A small ink dot on a paper is seen through s glass slab of thickness 4 cm and refractive index 1.5 . The dot appears to be raised by

    A
    `1 cm`
    B
    `2 cm`
    C
    `3 cm`
    D
    `1.33 cm`

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    B
    2 cm downwards
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