1.

A concave lens is in contact with convex lens. The ratio of magnitude of their power is 2/3. Their equivalent focal length is 30 cm. What are their individual focal lenghts ?

Answer»

`- 75, 50`
`- 10, 15`
75, 50
`-15, 10`.

Solution :(d) `(P_(1))/(P_(2)) = (f_(2))/(f_(1)) = - (2)/(3)`
`therefore "" f_(2) = - 2//3 f_(1)`
`(1)/(f_(1)) + (1)/(f_(2)) = (1)/(30)`
Solving we get `f_(1) = - 15 CM , f_(2) = 10 cm`


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