Question

Concave mirror of focal length 40cm produces an image twice the height of the object. If the image is real, then the distance of the object from the mirror is

Answer 1

Answer:

the distance of the object from the mirror is 20cm

Answer 2

The object distance is 20 cm

Explanation:

Given that,

Focal length = 40 cm

Height of image = 2 time height of object

We need to calculate the magnification

Using formula of magnification

$m = \dfrac{h'}{h}$

$m=\dfrac{2h}{h}$

$m=2$

We need to calculate the image distance

Using formula of magnification

$m=-\dfrac{v}{u}$

Put the value into the formula

$2=-\dfrac{v}{u}$

$v=-2u$

We need to calculate the object distance

Using formula of mirror

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

Put the value into the formula

$\dfrac{1}{40}=\dfrac{1}{-2u}+\dfrac{1}{u}$

$\dfrac{1}{u}=\dfrac{1}{20}$

$u = 20\ cm$

Hence, The object distance is 20 cm.

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Topic : Object distance

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