1989 B5

The piano-convex lens shown above has a focal length f of 20 centimeters in air. An object is placed 60 centimeters 3f from this lens.

(a) State whether the image is real or virtual.

(b) Determine the distance from the lens to the image.

(c) Determine the magnification of this image (ratio of image size to object size).

(d) The object, initially at a distance 3f from the lens, is moved toward the lens. On the axes below, sketch the image distance as the object distance varies from 3f to zero.

(e) State whether the focal length of the lens would increase, decrease, or remain the same if the index of refraction of the lens were increased. Explain your reasoning.