A compound lens is made of two lenses in contact having power $+ 12.5 D$ and $- 2.5 D$ . An object is placed at $15 c m$ from compound lens. Find the position of image formed

60 c m

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30 c m

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15 c m

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45 c m

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Solution

The correct option is B $30 c m$
$P_{1} = 12.5 D$
$P_{2} = - 2.5 D$
Equivalent power; $P = P_{1} + P_{2} = 12.5 - 2.5 = 10 D$
focal length equivalent $= \frac{100}{10} c m = 10 c m$ .
Given; $u = - 15 c m$
Using; $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$ ,
we get; $\frac{1}{v} = \frac{1}{f} + \frac{1}{u} = \frac{1}{10} - \frac{1}{15} = \frac{5}{150}$
$v = \frac{150}{5} = 30 c m$ .

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A compound lens is made of two lenses in contact having power +12.5D and −2.5D. An object is placed at 15 cm from compound lens. Find the position of image formed

The correct option is B 30 cmP1=12.5D P2=−2.5DEquivalent power; P=P1+P2=12.5−2.5=10 Dfocal length equivalent =10010cm=10cm.Given; u=−15 cmUsing; 1f=1v−1u,we get; 1v=1f+1u=110−115=5150v=1505=30 cm.

A compound lens is made of two lenses in contact having power $+ 12.5 D$ and $- 2.5 D$ . An object is placed at $15 c m$ from compound lens. Find the position of image formed