First slide

The lens

Question

The focal length of the field lens (which is an achromatic combination of two lenses) of telescope is 90 cm. The dispersive powers of the two lenses in the combination are 0.024 and 0.036. The focal lengths of two lenses are

Moderate

A

30 cm and 60 cm
B

30 cm and – 45 cm
C

45 cm and 90 cm
D

15 cm and 45 cm

Solution

For achromatic combination
$\frac{f_{1}}{f_{2}} = - \frac{ω_{1}}{ω_{2}} = - \frac{0 .024}{0 .036} = - \frac{2}{3} and \frac{1}{f_{1}} + \frac{1}{f_{2}} = \frac{1}{90} solving above equations be get f_{1} = 30 cm, f_{2} = - 45 cm$

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