Chapter 18, Problem 11STP

To determine

The type of lens used in the given case.

Answer to Problem 11STP

Concave lens since image distance is less than the object distance.

Explanation of Solution

Introduction:

The convex lens always produces a real and inverted image of the object on the other side of the lens as that of the object, except for the case when object distance is less than the focal length of the lens. For this case, virtual image is formed at the same side of the lens as that of the object. But, the image distance is greater than the object distance in this case.

However, the concave lens always forms the virtual image at the same side of the lens as that of the object and the image distance is always less than the object distance.

Since for the given case, image distance is less than the object distance and both lie on the same side of the lens, thus the type of lens used is a Concave lens.

Conclusion:

Hence, the concave lens is used for the given case.