Question

Rohit placed a pencil infront of converging mirror with focal length 30 cm. Find the distance of object of image formed is twice the height of object

Answer 1

In case of a mirror the magnification is given by  m = -v/u = h₀/h

                         where h₀ = height of image

                                     h = height of object

we are given magnification as 2

 therefore,  2 = -v/u

                    v = -2u

from the mirror formula ,

         1/f =  1/v + 1/u

putting f = -30 cm   and   v = -2u

        -1/30 = -1/2u + 1/u

        -1/30 =   1/2u

         u = -15 cm