Q. 9

# A compound microscope has a magnifying power of 100 when the image is formed at infinity. the objective has a focal length of 05 cm and the tube length is 6.5 cm. Find the focal length of the eyepiece.

Answer :

Given data -

Magnifying power of the compound microscope, *m* = 100

Objective lens focal length , *f*_{o} = 0.5 cm

Length of the tube, *l* = 6.5 cm

When the image is formed at infinity, image formed by the objective lens is real and it should lie

on the focus point of the eyepiece.

For normal adjustment, the magnifying power is -

We know that,

Solving (1) and (2)

*V*_{o} = 4.5 cm and *f*_{e} = 2 cm

Thus, the focal length of the eyepiece is 2 cm when the image formed is at infinity.

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