Q1.
Since the concave mirror converges the light beam, wouldn’t light get concentrated in a small area?
Answer
Yes, and that is exactly what happens. A concave mirror gathers light falling on its whole surface and delivers it to a very small patch — its focus.
Light falling on the mirror: spread over its full area
Light after reflection: crowded into a spot a few millimetres across
→ light energy per unit area at the spot becomes very much greater
Light after reflection: crowded into a spot a few millimetres across
→ light energy per unit area at the spot becomes very much greater
Why concentration means heating: light carries energy. A large mirror intercepts a lot of it. If all of that energy is then dumped on a tiny area of paper, the paper receives far more energy each second than it can lose to the surrounding air, so its temperature climbs — until it is hot enough to char and catch fire. Activity 10.7 is exactly this experiment.
Safety first: never look at the Sun, or at a mirror reflecting it, and never point the concentrated spot at anyone's face.