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Question
A convex lens of focal length f1 is kept in contact with a concave lens of focal length f2. Find the focal length of the combination.
Solution
For convex lens, focal length, f = f1 and for concave lens, the focal length, f = -f2
The equivalent focal length of a combination of convex lens and concave lens is given as:
`1/F = 1/f_1 +1/-f_2`
`=> F =(f_1f_2)/(f_2 -f_1)`
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