A point source S is placed midway between two converging mirrors having equal focal length f as shown in figure. Find the values of d for which only one image is formed.

Explanation

Both the mirrors have euqal focal length, f they will produce one image under two conditions
Case I: When the source is at distance 2f from each mirror i.e., the source is at centre of curvature of the mirrors, the images will be produced at the same point S. So, d=2f+2f=4f.
Case II: when the source S is at distance f from each mirror the rays from the source after reflecting from one mirror will become paralleand so these paralel rays after the reflection from the other mirror the object itself. So ony one image is formed.
Here `d=f+f2f`