Chapter 30, Problem 17A

Percy stands at different distances from a lens with a focal length of 30 cm. Rank the image distance from farthest to Percy to closest to Percy.

(A) Object is at 10

(B) Object is at 35 cm.

(C) Object is at 60 cm.

(D) Object is at 90 cm.

To determine

To rank: The image distance if object is moved away from the convex lens.

Explanation of Solution

Introduction:

A convex lens is also called converging lens as it converges all the beam of light incident on it to a single point called focus.

As a convex lens converges the beam of light incident on it, if the object is placed farther from the lens, the image moves closer to it. For example let’s consider two cases 1) when the object is at infinity, the image formed by the lens is at its focus 2) when the object is at focus, the image is formed at infinity.

These two examples clearly make it easy to understand that as the object is shifted towards the convex lens, it image shifts away from the lens and is also formed magnified. In the same way, as the object is shifted away from the lens, its image comes closer and closer to the lens and is smaller in size.

Conclusion:

Hence, based on the above facts, the image would be from farthest to lowest in a sequence A, B, C, D.