Question:
5 thin lenses each of 20 cm focal length are placed in contact with each other. The net power of this lens combination is
5 thin lenses each of 20 cm focal length are placed in contact with each other. The net power of this lens combination is
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Power adds up directly for lenses in contact.
Updated On: Apr 27, 2026
- 5D
- 20 D
- 10 D
- 25 D
- 15 D
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The Correct Option is D
Solution and Explanation
Step 1: Concept
Power $P = 1/f$ (in meters). For lenses in contact, $P_{net} = P_1 + P_2 + ... + P_n$.
Step 2: Meaning
Focal length $20 \text{ cm} = 0.2 \text{ m}$. Power of one lens $= 1 / 0.2 = 5$ D.
Step 3: Analysis
Net power $= 5 \times 5$ D $= 25$ D.
Step 4: Conclusion
The net power is 25 D.
Final Answer: (D)
Power $P = 1/f$ (in meters). For lenses in contact, $P_{net} = P_1 + P_2 + ... + P_n$.
Step 2: Meaning
Focal length $20 \text{ cm} = 0.2 \text{ m}$. Power of one lens $= 1 / 0.2 = 5$ D.
Step 3: Analysis
Net power $= 5 \times 5$ D $= 25$ D.
Step 4: Conclusion
The net power is 25 D.
Final Answer: (D)
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