: why does a flame give off light?
In: Physics
Why does anything give off light?
The answer is that many things emit energy, especially things that are hot, and some of that energy can be released in the visible spectrum of light so we see it.
Fire gives off light both because it has hot material, bits of wood or coal or even gas that burns, and because electrons get excited and change energy stages. The electron part is hard to ELI5, but it’s part of what flames are, and the process emits energy as light and heat.
It doesn’t, per se. It releases energy. Energy that we humans have adapted to being able to perceive with our eyes (due to it being an evolutionary advantage).
This takes a few key concepts that we’ll string together.
What makes light, at all.
All light comes from when an object with charge is “accelerated”. Bounce, bump, shake, speed up, spin etc, a charged object and it creates a wave in the electromagnetic field. We call this light.
Atoms have a charge, specifically the electrons that are bound to them. So if you shake and bounce atoms enough, you can create light.
Fire is a chemical reaction. The oxygen in the air reacts with the molecules of the item “burning”. This means it slams into the molecules, and snaps them into smaller parts that go flying off like debris in any collision.
Because these molecules and pieces got slammed into so hard, the electrons shake, and release light.
A lightbulb works in a similar way. Except instead of oxygen slamming into molecules we run electricity through the bulb, a river of flowing electrons that bump and shake the atoms of the filament as they pass by.
LED’s are also similar, except they work more like making the river of electrons make the light itself. The LED essentially is a stair step “waterfall” or “electricity-fall” and as the electrons fall over the edge, they bump and release light at the bottom.
Radio and Cell-phone antennae do this too. They pass electricity back and forth along the wire that is antenna. This shaking of the electrons create the radio “light” that other devices pick up.
A flame is a chemical reaction that is the rapid oxidation of a fuel and oxygen. This reaction is exothermic, meaning it gives off energy. This energy is released is many kinds of ways but one big part is invisible Infrared radiation. This invisible radioaction is what you feel as heat. You can feel it in your hands your face. It’s what makes a good campfire
Another big component of the reaction is output chemicals. In many types of fuel reactions, the major outputs are carbon dioxide and water vapor. But one other piece is sometimes just carbon, commonly referred to as soot. The black stuff that builds up on the bottom of pot when you cook over a campfire.
What happens when you take soot and mix it with infrared energy? Just like how infrared heats up your hand, it also hears up the soot. In fact it makes the soot really high temperature. Several hundred degrees. At that point, soot is so hot it glows. A dull red color to start, then bright orange and yellow. That’s the flame portion that you see of a fire.
Some kinds of fuel fires don’t produce a lot of soot, like well oxygenated natural gas or rubbing alcohol. All you get is a small blue flame.
Other fuel fires don’t produce any soot at all but instead emit ultraviolet light that we can’t see. Methanol race gas is this kind. It leads to invisible fires that leads to a dance of death for driver and crew that’s trapped in the fire. It causes problems with firefighting teams because they don’t even know where to point the fire extinguisher or how far away they are from the fire. These fires are very dangerous and very deadly
Latest Answers