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

Asked by deepika babbar | 16th Dec, 2013, 12:29: PM

Expert Answer:

The equivalent focal length of two lenses in contact is
 
 
It is given that f = 30 cm
and f1/f2 = -2/3  (Concave lens will have negative focal length, so the ratio will also be negative)
 
Thus, we have
 

Answered by Romal Bhansali | 16th Dec, 2013, 12:46: PM

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