# A Converging Lens is Kept Coaxially in Contact with a Diverging Lens – Both the Lenses Being of Equal Focal Length. What is the Focal Length of the Combination? - Physics

A converging lens is kept coaxially in contact with a diverging lens – both the lenses being of equal focal length. What is the focal length of the combination?

#### Solution

The focal length of the lenses is f and −f.

We know that the equivalent focal length of a combination of lenses is

1/f_e""=1/f_1""+1/f_2""=1/f-1/f=0

:.f_e = oo

Concept: Refraction at Spherical Surfaces and Lenses - Combination of Thin Lenses in Contact
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