An object,located 90 cm from a concave lens,forms an image 30 cm from the lens on the same side as the object.What is the focal length of the lens?
A) −150 cm
B) −45 cm
C) −36 cm
D) −180 cm

Question

Quizplus · Accepted Answer

The lens formula is 1/f = 1/v - 1/u. Here, v = -30 cm (since the image is on the same side as the object) and u = -90 cm. Plugging these values in gives 1/f = 1/(-30) - 1/(-90) = -1/45, so f = -45 cm.

An Object,located 90 Cm from a Concave Lens,forms an Image