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A convex lens of focal length 30 cm and ...

A convex lens of focal length 30 cm and a concave lens of 10 cm focal length are placed so as to have the same axis. If a parallel beam of light falling on convex lens leaves concave lens as a parallel beam, then the distance between two lenses will be

A

40 cm

B

30 cm

C

20 cm

D

10 cm

Text Solution

Verified by Experts

The correct Answer is:
C
`(1)/(f_(eq)) = (1)/(f_(1)) + (1)/(f_(2)) - (d)/(f_(1) f_(2))`
`rArr (1)/(infty) = (1)/(30 ) - (1)/(10) - (d)/((30)(-10))`
`rArr d = 20 ` cm.
(as combination behaviour is like plane glass)
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