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>> $If the focal length of objective and eye$

Question

If the focal length of objective and eye lens are 1.2 cm and 3 cm respectively and the object is put 1.25 cm away from the objective lens and the final image is formed at infinity. The magnifying power of the microscope is :

A

150

B

200

C

250

D

400

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Updated on : 2022-09-05

Solution

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Correct option is B)

Using the lens formula for the objective lens,

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

$\frac{1}{1 . 2} = \frac{1}{v} - \frac{1}{- 1 . 2 5}$

This gives $v = 30 c m$
Now, magnification is given $m = \frac{v}{u} \times \frac{D}{f _{e}}$

Substituting the values, $m = \frac{3 0}{1 . 2 5} \times \frac{2 5}{3}$

Thus, $m = 200$

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