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A convex lens if in contact with concave...

A convex lens if in contact with concave lens. The magnitude of the ratio of their focal length is `(2)/(3)`. Their equivalent focal length is 30 cm. What are their individual focal lengths?

A

`-75, 50 `

B

` – 10.15`

C

75,50

D

10.-15

Text Solution

Verified by Experts

The correct Answer is:
D
` (f_(1))/( f_(2)) = (2)/(3)`
and ` (1)/( f_(eq)) = (1)/(f_(1)) + (1)/(f_(2))`
`rArr (1)/(30) = (1)/(f_(1)) - (1)/(f_(2))`
`rArr (1)/(30) = (1)/( f_(1)) - (2)/( 3 f_(1)) = ( 3 - 2)/( 3 f_(1))`
`rArr f_(1) = 10 cm, f_(2) = - 15 cm`
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