A combination of convex and concave lenses has power $4 D$ .If the convex lens has power $5 D$ focal length of the concave lense will be

100 c m

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- 100 c m

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- 1 c m

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- \frac{100}{9} c m

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Solution

The correct option is B $- 100 c m$
Power of combination
$P = P_{1} + P_{2}$
$\Rightarrow 4 = 5 + P_{2}$
$\Rightarrow P_{2} = 4 - 5 = - 1 D$
$∴ - 1 = P_{2} = \frac{100}{f (c m)}$
$∴ f = - 100 c m$

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A combination of convex and concave lenses has power 4D .If the convex lens has power 5D focal length of the concave lense will be

The correct option is B −100cmPower of combination P=P1+P2⇒4=5+P2⇒P2=4−5=−1D∴−1=P2=100f(cm)∴f=−100cm

A combination of convex and concave lenses has power $4 D$ .If the convex lens has power $5 D$ focal length of the concave lense will be

The correct option is B $- 100 c m$
Power of combination
$P = P_{1} + P_{2}$
$\Rightarrow 4 = 5 + P_{2}$
$\Rightarrow P_{2} = 4 - 5 = - 1 D$
$∴ - 1 = P_{2} = \frac{100}{f (c m)}$
$∴ f = - 100 c m$