#### Question

A convex lens of focal length f_{1} is kept in contact with a concave lens of focal length f_{2}. Find the focal length of the combination.

#### Solution

For convex lens, focal length, f = f_{1} and for concave lens, the focal length, f = -f_{2}

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)`

Is there an error in this question or solution?

Solution 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. Concept: Concave Mirror.