Question

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

Answer 1

f = 30cm

1/f = 1/v - 1/u

1/30 = 1/20 - 1/u

1/u = 1/20 - 1/30

= 1/60 = 1/60

∴the object should be placed from a distance of 60 cm.

hope it helps

please mark brainliest