Yes, it is possible to start a fire using a plane mirror and sunlight. This method of starting a fire is known as the "mirror or lens fire-starting technique." The underlying physics involved is the concentration of sunlight into a small focal point, which generates enough heat to ignite combustible materials.
The key principle at work is the reflection and concentration of light by the mirror. When sunlight strikes a mirror's surface, it reflects off the mirror following the law of reflection, which states that the angle of incidence is equal to the angle of reflection. By adjusting the angle of the mirror, you can control the direction in which the reflected light is directed.
To start a fire, you need to focus the reflected sunlight onto a specific point. A plane mirror, being flat and without any curvature, spreads the reflected light over a wider area. However, if you position the mirror correctly, it can redirect the sunlight towards a specific spot, creating a concentrated beam.
To achieve the concentration of sunlight, you would typically use a convex lens or a parabolic mirror, as they are curved and can focus the light more effectively. Nevertheless, even with a plane mirror, you can still create a concentrated beam by angling the mirror to reflect sunlight onto a specific spot.
Once the sunlight is focused on a small area, the intensity of the light increases significantly, resulting in a substantial amount of heat. If this concentrated beam falls onto a flammable material such as dry leaves, paper, or tinder, it can raise the temperature of the material to its ignition point, causing it to catch fire.
It's important to exercise caution when using this technique, as the concentrated beam of sunlight can be intense and potentially hazardous. Ensure that you are aware of fire safety precautions and never direct the focused beam towards people, buildings, or other objects that could be harmed.
Note that this method works best under optimal conditions, such as when the sun is high in the sky, the mirror is clean and reflective, and you have suitable tinder or combustible material to ignite.