Question

An object is X, focal length to left of principal focus of a concave mirror. Show that the image will be 1/X , of focal length to left of the focus?

Answer 1

The primary focal point (F1) of a lens is also called the Object-Space Focus.Secondary focal point (F2) of a lens is also called the Image-Space Focus. For a plus lens, this is the point where parallel rays from a distant point object are rejoined to form an image at that point.

Answer 2

The distance between the pole P of the concave mirror and the focus F is the focal length of the concave mirror. Thus, the focal length of a concave mirror can be estimated by obtaining a 'Real image' of a distant object at its focus, as shown in the figure.