Question

A concave lens has a focal length 20 cm. At what distance should the object from the lens be placed so that it forms the image at a distance 10 cm from the lens?

Answer 1

answer that is object distance is -20 CM

Answer 2

here f=-20cm
v=-10cm
1/f=1/v-1/u
-1/20=-1/10-1/u
-1/u=-1/20
u=-20cm