# A Simple Microscope Has a Magnifying Power of 3.0 When the Image is Formed at the Near Point (25 Cm) of a Normal Eye. - Physics

A simple microscope has a magnifying power of 3.0 when the image is formed at the near point (25 cm) of a normal eye. (a) What is its focal length? (b) What will be its magnifying power if the image is formed at infinity?

#### Solution

For the simple microscope, we have:
Least distance of clear vision, D = 25 cm
Magnifying power, m = 3
Now,
Let the focal length be f.

(a) When the image is formed at D = 25 cm, the magnifying power of the simple microscope is given by

m = 1 + (D/f)

=> 3 =1+(25/f)

=> 25/f = 2

=> f = 25/2 = 12.5  "cm"

(b) When the image is formed at infinity in normal adjustment, the magnifying power is given by

m = D/f = 25/12.5 =2.0

So, the magnifying power is 2 if the image is formed at infinity.

Concept: Magnification
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#### APPEARS IN

HC Verma Class 11, 12 Concepts of Physics 1
Chapter 19 Optical Instruments
Q 3 | Page 432