1.

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. `-15,10`B. `-10,15`C. `75,50`D. `-75,50`

Answer» Correct Answer - A
`|f1|/|f2|=(2)/(3)`
f1: focal length of convex lens. `(1)/(f)=(1)/(f2)-(1)/(f2)` `implies (1)/(30)=(1)(f1)=(2)/(3f1)`
1f_(1)=10 cm, `f_(2)=-15 cm`


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