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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

`75,50`

C

`10,-15`

D

`-75,50`

Text Solution

Verified by Experts

The correct Answer is:
C
`P=(1)/(f)rArr (P_(1))/(P_(2))=(f_(2))/(f_(1))=-(3)/(2)`
Let focal length of convex lens is `f_(1)=f`than focus length of concave length `f_(2)=-(3f)/(2)`
So,`(1)/(30)=(1)/(f)-(2)/(3f)`
`(1)/(30)=(3-2)/(3f)`
`f=10cm`
`f_(1)=10cm,f_(2)=-15cm`
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