An object is placed on an optical bench. A lens with a focal length of 15 cm is placed 30 cm from the object. A diverging lens with a focal length of -10 cm is placed 7.0 cm beyond that. Where is the final image formed, relative to the second lens?
A)45 cm beyond the diverging lens
B)20 cm behind the diverging lens
C)18 cm behind the diverging lens
D)17 cm beyond the diverging lens
E)30 cm beyond the diverging lens

Question

Quizplus · Accepted Answer

First, use the lens formula for the converging lens to find the image distance: 1/f = 1/v - 1/u, where f = 15 cm and u = -30 cm. This gives v = 30 cm. This image acts as the object for the diverging lens, with an object distance of 30 - 7 = 23 cm. Using the lens formula for the diverging lens with f = -10 cm, we find the final image distance v = -18 cm, meaning 18 cm behind the diverging lens.

An Object Is Placed on an Optical Bench