Question

a convex lens is in contect with concave lens. the magnitude of the ratio of their focal length is 2/3 their equivalent focal length is 30cm their individual focal length in cm will be:-
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Answer 1

Answer:

For Convex lens f = 10cm and for concave lens f = -15cm

Explanatilet focal length for convex lens be f1 and concave lens be f2

Then according to condition

Mod(f1 / f2) = 2/3. ................ (1)

For focal length of combination

Formula used is

(1/F) = (1/f1) + (1/ f2) (with sign)

(1/30) = (1/f1) - (2/3f1) ...... (from (1))

On solve f1 =10cm and f2= -15cm