Question

A converging mirror from a real image of height 4 cm of an object of height 1 cm placed 20 cm away from the mirror .Calculate the image distance.What is the focal length of the mirror?

Answer 1

converging mirror  = concave mirror.
real image = inverted image. 
   image size  h' = - 4 cm
   h = 1 cm
      =>  magnification m = h'/h = -4
       as m  = -v/u = -4 and u = -20 cm
       =>  v = 4 u  = - 80 cm

   write mirror equation and solve for focal length f.
       1/f = 1/v + 1/u = -1/20 -1/80 = -1/16
                f  = -16 cm