An object is placed at one of the two focal points of a thin converging lens. Where will its image form? A. the other focal point of the lens
B. in the middle of the lens
C. an infinite distance from the lens
D. the same position as the object

C. an infinite distance from the lens

Explanation:

There are five distinct cases of image formation in a convex lens depending upon the position of an object:

1. When the object is placed at an infinite distance from the lens, its real image is formed at the focal point.

2. When the object is placed before the center of curvature of the lens, its real image is formed between the center of curvature and the focal point.

3. When the object is placed at the center of curvature of the lens, its real image is formed at the center of curvature.

4. When the object is placed between the center of curvature and the focal length of the lens, its real image is formed behind the center of curvature.

5. When the object is placed at the focal point of the lens, its virtual image is formed at infinity.

Hence, from point 5 the answer is:

C. an infinite distance from the lens