Ellen places an object 40.0 cm from a concave lens.If a virtual image appears 10.0 cm from the lens on the same side as the object,what is the focal length of the lens?

Question

Quizplus · Accepted Answer

The lens formula is 1/f = 1/v - 1/u. Here, u = -40 cm (object distance, negative for lenses), v = -10 cm (image distance, negative for virtual images). Solving gives 1/f = 1/(-10) - 1/(-40) = -1/10 + 1/40 = -3/40, so f = -13.3 cm.

Ellen Places an Object 40