Question

size of the image formed by concave lens
of focal length 20 is observed to be reduced by 1/3 of its size find the distance of the object from the lens

Answer 1

1/f=1/u-1/v

1/20=1/u-1/1/3

1/u=3+1/20

=60+1/20

=61/20

u =20/61

=0.32