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Question
An object P is focussed by a microscope M. A glass slab of thickness 2.1 cm is introduced between P and M. If the refractive index of the slab is 1.5, by what distance should the microscope be shifted to focus the object again?
Solution
Given,
Thickness of the glass slab, d = 2.1 cm
Refractive index, μ = 1.5
Shift due to the glass slab is given by,
\[∆ t = \left[ 1 - \left( \frac{1}{\mu} \right) \right]d\]
\[= \left[ 1 - \left( \frac{1}{1 . 5} \right) \right]\left( 2 . 1 \right)\]
\[= \frac{1}{3}\left( 2 . 1 \right) = 0 . 7 cm\]
Hence, the microscope should be shifted by 0.70 cm to focus the object 'P' again.
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