Question

You’ve been asked to build a telescope from a 2.0X magnifying lens and a 5.0X magnifying lens.

a. What is the maximum magnification you can achieve?

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b. Which lens should be used as the objective? Explain.

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c. What will be the length of your telescope?

Answer 1

MODEL:

For relaxed-eye viewing, the angular magnification is

Here, the focal length of the lens is f.

VISUALIZE:

The angular magnification of a telescope is

. . . . . . (1)

Here, the objective focal length is and the eyepiece focal length is .

SOLVE:

(a)

For objective, the angular magnification can be expressed as

Thus, the objective focal length can be written as

Similarly, the eyepiece focal length can be written as

Substituting the above relations in the equation (1),

Thus, the magnification of the telescope is

The magnitude of this magnification will be maximum only when the magnification of the eyepiece is greater than the magnification of the object. That is.

Hence, the magnification of the telescope is

The value of the magnification of the telescope must take in positive sign, so it is.

(b)

The magnitude of the magnification of telescope will be maximum only when the magnification of the eyepiece is greater than the magnification of the object. That is.

The magnifying glass acts as objective because its magnification is less than the magnification of the other magnifying glass.

(c)

Length of the our telescope is