Question

You have a concave (diverging) lens with a −31 cm focal length. The magnification produced by the lens for a particular object distance is m = 1/2 and you wish to decrease the magnification to m = 1/5. Determine the distance and direction (away from or closer to the lens) through which the object must be moved in order to accomplish this.

Answer 1

f=-31 cm (for diverging lens)

v= image distance

u= object distance

m= magnification =v/u

we know the diverging formula

   ............................................(1)

when m=1/2

so, u=2v ...................(2)

from equation (1)

  

And u= 2v= 2*(-46.5)= -93 cm

When m=1/5

v/u=1/5

u=5v...............................(3)

From equation (1)

v= -37.2 cm

And u= 5v = 5(-37.2)= -186 cm

Answer is distance change

the distance change is =93 cm image go to object side