An object of size $10 cm$ is placed at a distance of $30 cm$ from a concave mirror of focal length $20 cm$ . The size of the image formed is -

10 cm

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30 cm

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20 cm

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15 cm

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Solution

The correct option is C $20 cm$
Given:
$h_{o} = 10 cm$
$u = - 30 cm$
$f = - 20 cm$

Using mirror formula,

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

$\Rightarrow \frac{1}{(- 20)} = \frac{1}{v} + \frac{1}{(- 30)}$

$\Rightarrow v = - 60 cm$

Magnification for mirror is,

$m = \frac{- v}{u} = \frac{h_{i}}{h_{o}}$

$\Rightarrow \frac{h_{i}}{10} = \frac{- (- 60)}{(- 30)}$

$\Rightarrow h_{i} = - 20 cm$

Hence, option $(C)$ is the correct answer.

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(3 Marks)

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An object of size 10 cm is placed at a distance of 30 cm from a concave mirror of focal length 20 cm. The size of the image formed is -

The correct option is C 20 cmGiven: ho=10 cm u=−30 cm f=−20 cm Using mirror formula, 1f=1v+1u ⇒1(−20)=1v+1(−30) ⇒v=−60 cm Magnification for mirror is, m=−vu=hiho ⇒hi10=−(−60)(−30) ⇒hi=−20 cm Hence, option (C) is the correct answer.

An object of size $10 cm$ is placed at a distance of $30 cm$ from a concave mirror of focal length $20 cm$ . The size of the image formed is -