Answer the following question.
Why does obtaining the image of the sun on a paper with the help of a concave mirror burn the paper?
The rays from the Sun are parallel. When these rays fall on the concave mirror, they are converged to a single point on the focal plane of the mirror. Thus a lot of heat is produced at that point. Now, if a paper is placed at that point to get the image of the Sun, the paper gets burnt because of huge amount of heat concentrated at that point.