Physics 2003 JAMB Past Questions - Question 23: At what position will an object be placed in front of a concave mirror in order to obtain an image at infinity?

Correct Answer

E

Explanation

for a concave mirror to produce an image at infinity, the object has to be placed at a principal focus of the mirror.To obtain an image at infinity using a concave mirror, you need to place the object at the focal point of the mirror. For a concave mirror, the focal point (F) is located on the same side as the object and is typically half the distance of the mirror's radius of curvature (R) from the mirror's surface.

So, if you place the object at a distance equal to the focal length (f) in front of the concave mirror, the resulting image will appear at infinity. The position of the object would be specifically at a distance of one focal length from the mirror.

In mathematical terms:
Object distance (p) = Focal length (f)

This is known as the "focus at focus" position, and it will create a parallel light bundle that appears to come from infinity when it reflects off the mirror.