Two very thin lenses, each with focal length 20. cm, are placed in contact. What is the focal length of this compound lens?

Name: Two very thin lenses, each with focal length 20. cm, are placed in contact. What is the focal length of this compound lens?
Brand: Quizplus
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Question

Quizplus · Accepted Answer

When two lenses are in contact, the combined focal length (F) is given by 1/F = 1/f1 + 1/f2. Here, both lenses have a focal length of 20 cm, so 1/F = 1/20 + 1/20 = 1/10. Thus, the focal length of the compound lens is 10 cm.

Two Very Thin Lenses, Each with Focal Length 20