A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is :

Question

Dr. Abubacker · Accepted Answer

[Solution from source] The powers are +1/0.25 = +4 D for the convex lens and −4 D for the concave lens. In contact the total power is 4 − 4 = 0, so the combination acts like a plane glass plate. Zero power means infinite focal length, not infinite power. Answer (4).

Q. A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is :

Explanation

Reviewed by Dr. Abubacker

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