100. An amateur astronomer decides to build a telescope from a discarded pair of eyeglasses. One of the lenses has a refractive power of 11 diopters, and the other has a refractive power of 1.3 diopters. (a) Which lens should be the objective? (b) How far apart should the lenses be separated? (c) What is the angular magnification of the telescope?

Normally you want the objective to have a longer focal length and the eye piece to have a shorter focal length. So Power is the inverse of focal length. Therefore, the smaller power has the longer focal length and should be the objective which is the 1.3 diopter lens.

The distance between the lenses should be the sum of the focal lengths, so

Find each focal length, onjective

For eye piece

magnification

Objective lens should be the 1.3 diopter lens.

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