Q. 12

# An astronomical telescope is to be designed to have a magnifying power of 50 in normal

adjustment. If the length of the tube is 102 cm, find the powers of the objective and the eyepiece.

Answer :

Given data -

Magnifying power of the astronomical telescope, *m* = 50

Length of the tube, *L* = 102 cm

Let *f*_{0} and *f*_{e}, be the focal length of objective and eye piece

Then using the formula for magnification, m

Substituting the values-

Also

Substituting (2) in (1)

And, substituting the value in (1)

Hence, the power, which is reciprocal of focal length becomes-

For objective lens -

And,

For eye piece lens

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