Ncert Exercises & Solutions

The near vision of an average person is 25 cm. To view an object with an angular magnification of 10, what should be the power of the microscope?

Hint: Use the formula of the magnification.

Step 1: Find the focal length of the lens.

The least distance of distinct vision of an average person (i.e., D) is 25cm, in order to view an object with a magnification of 10.
Here, v = D = 25cm and u = f
But the magnification, m=v/u =D/f
$m = \frac{D}{f}$
$\Rightarrow$ $f = \frac{D}{m} = \frac{25}{10} = 2.5 = 0.025 m$

Step 2: Find the power of the lens.
$P = \frac{1}{0.025} = 40 D$
This is the required power of lens.

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