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 dioptres) of the combination is:
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Question

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 dioptres) of the combination is:

G1 Physics · Accepted Answer

Step 1: Powers add for thin lenses in contact. Step 2: P₁ = 1/0.25 = +4 D and P₂ = 1/(−0.25) = −4 D. Step 3: P_total = 4 − 4 = 0 D. Final answer: (A) Zero.