Question

​ When an object is placed at a distance of 60 cm from a convex spherical mirror the magnification produced is 1/2 where should the object be placed to get a magnification of 1/3

Answer 1

v = 30 cm,

So, we come to know that, 

v = 30 cm  when u = -60 cm

So the focal length of the mirror  is f,

Using the mirror formula,

1/u + 1/v = 1/f

-1/60 + 1/30 = 1/f

f = 60 cm

For magnification equal to 1/3.

1/3 = -v/u

v = -(1/3)u  and f = 60 cm ...(i)

Using the mirror formula,

1/u + 1/v = 1/f

Putting qe. (i),

1/u-3/u = 1/60 

 u = -120 cm