A diverging lens, focal length $f_{1} = 20 cm$ is separated by 5 cm from a converging mirror, focal length $f_{2} = 10 cm$ . Where should an object be placed from the lens so that a real image is formed at the object itself ?

30 cm

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60 cm

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10 cm

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40 cm

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Solution

The correct option is B
60 cm

For lens $f = - 20$ , $u = ?$ , $v = - (20 - 5) = - 15$

$\frac{1}{- 20} = \frac{1}{- 15} - \frac{1}{u}$

$\frac{1}{u} = \frac{1}{20} - \frac{1}{15}$

$u = - 60$

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A diverging lens, focal length f1=20 cm is separated by 5 cm from a converging mirror, focal length f2=10 cm. Where should an object be placed from the lens so that a real image is formed at the object itself ?

The correct option is B 60 cm For lens f=−20, u=?, v=−(20−5)=−15 1−20=1−15−1u 1u=120−115 u=−60

A diverging lens, focal length $f_{1} = 20 cm$ is separated by 5 cm from a converging mirror, focal length $f_{2} = 10 cm$ . Where should an object be placed from the lens so that a real image is formed at the object itself ?

The correct option is B
60 cm

For lens $f = - 20$ , $u = ?$ , $v = - (20 - 5) = - 15$

$\frac{1}{- 20} = \frac{1}{- 15} - \frac{1}{u}$

$\frac{1}{u} = \frac{1}{20} - \frac{1}{15}$

$u = - 60$