Question

an object is placed at a distance of 20 cm before a concave mirror . A real image is obtained at a distance of 40 cm from the mirror . Calculate the focal length of the mirror and the magnification

Answer 1

Solution is in pic
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Answer 2

Sol :-

Object position = -20 cm

Image position = -40 cm ( Since it is real )

Using Mirror's formula , 

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

We get - 1/-40 + 1/ -20 = 1/f
 
           
            -3/40 = 1/f
 
                So f ( Focal length ) = - 40 / 3

Magnification = - v/u = -(-40)/-20 = -2 ,so the image is real !