Question

A telescope consists of two lenses of focal length 100 cm and 5 cm. Find the magnifying power when the final image is formed at infinity.

Hint:

The magnifying power of a telescope is simply the ratio of the focal length of the objective lens to the focal length of the eyepiece when the final image is formed at infinity.

Answer 1

In a telescope, the magnifying power \( M \) is given by the ratio of the focal lengths of the objective and the eyepiece: \[ M = \frac{f_o}{f_e}. \] Here, \( f_o = 100 \, \text{cm} \) and \( f_e = 5 \, \text{cm} \), so the magnifying power is: \[ M = \frac{100}{5} = 20. \] Thus, the magnifying power of the telescope is 20.