First slide

The optical instruments

Question

The focal length of objective and eye lens of a astronomical telescope are respectively 2 m and 5 cm. Final image is formed at (i) least distance of distinct vision (ii) infinity. The magnifying power in both cases will be

Moderate

A

– 48, – 40
B

– 40, – 48
C

– 40, 48
D

– 48, 40

Solution

When the final image is at the least distance of distinct vision, then
$m = - \frac{f_{o}}{f_{e}} (1 + \frac{f_{e}}{D}) = \frac{200}{5} (1 + \frac{5}{25}) = \frac{200 \times 6}{5 \times 5} = - 48$
When the final image is at infinity, then
$m = \frac{- f_{o}}{f_{e}} = \frac{200}{5} = - 40$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App