Question

How far an object should be placed from the concave mirror of focal length 3m in order to obtain an image on the screen 9m away from the mirror​

Answer 1

Answer:

$\dfrac{9}{2} m$

Explanation:

It is given that it is a concave mirror.

Focal length, $f = 3m$

Distance of image, $v = 9m$

To find:

The distance of object, $u =?$

We know the mirror formula as:

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

Where 'f' is the focal length of concave mirror

'u' is the distance of object from the mirror and

'v' is the distance of image from the mirror

Putting the values of 'f' and 'v' in the formula and finding the value of 'u':

$\dfrac{1}{3} = \dfrac{1}{u}+\dfrac{1}{9}\\\Rightarrow \dfrac{1}{u} = \dfrac{1}{3}-\dfrac{1}{9}\\\Rightarrow \dfrac{1}{u} = \dfrac{3-1}{9}\\\Rightarrow \dfrac{1}{u} = \dfrac{2}{9}\\\Rightarrow u = \dfrac{9}{2} m$

Hence, the object should be placed at a distance 4.5m away from the mirror in order to obtain an image on the screen 9m away from the mirror.

Answer 2

Answer:

4.5 m

Explanation:

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