find the position of an object when placed in front of a concave mirror of focal length 20 cm produces a virtual image,which is twice size of object.


focal length 

f= -20cm

and magnification

m = +2 = -v/u


v= -2u_______(1)

now, the mirror relation is

1/f = 1/v + 1/u


-1/20 = u + v/uv

            = u-2u /-2u2   [substituting value of v from eq. (1)]

thus, image distance will be

u= -10cm

  • 50
What are you looking for?