If the tube length of astronomical teles...

If the tube length of astronomical telescope is 105 cm and magnifying power is 20 for normal setting, then the focal length of the objective is .......... cm.

A

100

B

90

C

105

D

92

Verified by Experts

The correct Answer is:

B

`|m| = f_0/(f_e) = 15`
`f_0 = 15 f_e`
tube length `=f_0 + f_e = 96`
`15f_e + f_e = 96`
`f_e = 6 cm`
`f_0 = 15 xx 6 = 90 cm`

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