CAUTION: Do not look at the Sun directly or even into a mirror reflecting sunlight. It may damage your eyes.
Hold a concave mirror in your hand and direct its reflecting surface towards the Sun.
Direct the light reflected by the mirror on to a sheet of paper held close to the mirror.
Move the sheet of paper back and forth gradually until you find on the paper sheet a bright, sharp spot of light.
Hold the mirror and the paper in the same position for a few minutes. What do you observe? Why?
✅ Answer: The paper burns and catches fire. This is because the light from the Sun is converged (concentrated) at a point of paper as a bright spot (image of the Sun). This point is the focus of the concave mirror. It produces heat and ignites the paper.