Question

The focal length of a concave lens is 30 cm at what distance should the object be placed from the lens so that its forms an image at 20 cm from the lens

Answer 1

Lens formula:1/f=1/v_1/u

1/_30=1/_20_1/u

_1/30+1/20=1/u

1/60=_1/u

u=_60cm