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Two thin lenses of power +3 D and -1 D are kept in contact. The net power is:
A-2 D
B+4 D
C+2 D
D+3 D
Answer & Solution
Correct answer: C. +2 D
1. Powers of lenses in contact add algebraically.
2. P_net = P₁ + P₂ = (+3) + (-1) = +2.
3. The combination behaves as a single converging lens of +2 D.
_Source: NCERT Class 10 Science, Ch 9 "Light Reflection and Refraction", §9.4.4_
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