A telescope consists of two lenses of focal lengths `20 cm and 5 cm`. Obtain its magnifying power when final image is
(i) at infinity
(ii) at `25 cm` from the eye.

Answer

(i) `- 4` (ii) `- 4.8`

Explanation

When final image is at infinity,
`m = (f_(0))/(f_(e)) = (-20)/(5) = - 4`
When final image is at `d = 25 cm` ,
`m = (-f_(0))/(f_(e)) (1 + (f_(e))/(d)) = (-20)/(5)(1 +(5)/(25)) = - 4.8`