Question

a concave lens of 20 cm focal length forms an image 15 cm from the lens. Compute the object distance.​

Answer 1

The lens formula says that-

1/v -1/u=1/f

where, v=image distance=-15 cm,as the image will form behind the lens.

          u=object distance=?

           f=focal length=-20 cm

so after putting these values in the lens formula we wiil be getting u=60cm behind the lens

Answer 2

Solution:

Therefore the object distance is -60

cm.