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Standard XII

Physics

Mirror Formula Formal Proof

Consider the ...

Question

Consider the situation as shown in the figure. A point object O is placed at a distance of 20 cm from a concave lens of focal length 5 cm. Now a concave mirror of radius 9 cm is adjusted on the right side of the lens, so that the final image coincides with the object O. Find the separation between the lens and the mirror.

4 cm

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9 cm

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5 cm

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3 cm

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Solution

The correct option is C
5 cm

The image formed by the lens will be at the centre of curvature of the mirror.
For lens

$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$\frac{1}{v} - \frac{1}{(- 20)} = \frac{- 1}{5}$

$v = - 4 c m$

Hence distance between the lens and the mirror is 5 cm.

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The correct option is C 5 cm The image formed by the lens will be at the centre of curvature of the mirror. For lens 1v−1u=1f 1v−1(−20)=−15 v=−4 cm Hence distance between the lens and the mirror is 5 cm.

The correct option is C
5 cm

The image formed by the lens will be at the centre of curvature of the mirror.
For lens

$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$\frac{1}{v} - \frac{1}{(- 20)} = \frac{- 1}{5}$

$v = - 4 c m$

Hence distance between the lens and the mirror is 5 cm.