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Three thin lenses having powers 2 D, 2.5 D and 1.7 D are placed touching one another in a row. What is the total power of this combination?
A2.5 D
B0.16 D
C6.2 D
D10.6 D
Answer & Solution
Correct answer: C. 6.2 D
1. For lenses in contact, the effective power equals the sum of individual powers: P = P1 + P2 + P3.
2. P = 2 + 2.5 + 1.7.
3. P = 6.2 D; taking the largest single value or adding focal lengths gives the wrong answers.
_Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 7 "Lenses", p.101_
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