A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

- 1.5 D

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- 6.5 D

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+ 6.5 D

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+ 6.67 D

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Solution

The correct option is A - 1.5 D
$P = P_{1} + P_{2} = \frac{1}{f_{1}} + \frac{1}{f_{2}} = \frac{1}{0.4} - \frac{1}{0.25} ∴ P = - 1.5 D$

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A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

The correct option is A - 1.5 DP=P1+P2=1f1+1f2=10.4−10.25∴P=−1.5D

The correct option is A - 1.5 D
$P = P_{1} + P_{2} = \frac{1}{f_{1}} + \frac{1}{f_{2}} = \frac{1}{0.4} - \frac{1}{0.25} ∴ P = - 1.5 D$