A convex lens of focal length 20 cm is in contact with a concave lens of focal length 40 cm. The power of the combination is:
Show Hint
- +2.5 D
- -2.5 D
- +5.0 D
- -5.0 D
The Correct Option is A
Solution and Explanation
$P_{net} = P_{1} + P_{2} = 1/f_{1} + 1/f_{2}$.
Step 2: Analysis
$P_{1} = 1/0.2 = +5 D$. $P_{2} = 1/(-0.4) = -2.5 D$.
Step 3: Conclusion
$P_{net} = 5 - 2.5 = +2.5 D$.
Final Answer: (A)
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