Eli5 Why does metal give off light when heated?
In: Chemistry
All materials do this. As atoms bounce around off of each other, their electrons vibrate. Electrons vibrating, or at least getting flung around, is the primary source of electromagnetic radiation. Like a radio antenna, but much smaller.
Metals actually don’t do it nearly as effectively as darker materials, like ceramics or carbon.
Human bodies glow like this, but in infrared light. As objects get hotter, the glow becomes bluer and bluer, from far-IR to near-IR to red to white to blue, hotter and hotter.
When you heat up a material you’re giving it energy. The law of conservation of energy tells you that that energy can’t just disappear. Some of that energy of course goes in to heat energy. Some of that goes in to other things. Such as being “converted” light.
To explain it in a little more detail (I’m not chemist so correct me if I’m wrong) :
When electrons are given energy, such as by heat, they become unstable and their energy level isn’t sustainable. In an MO diagram we visualize this by literally moving the electron up. But they can’t stay up. They’re unstable. So on their way down, they release energy.
If you want to learn about MO diagrams:
[https://chem.libretexts.org/Courses/University_of_California_Davis/UCD_Chem_110A%3A_Physical_Chemistry__I/UCD_Chem_110A%3A_Physical_Chemistry_I_(Larsen)/Lectures/27%3A_Molecular_Orbitals_with_higher_Energy_Atomic_Orbitals_(Extra_Lecture)](https://chem.libretexts.org/Courses/University_of_California_Davis/UCD_Chem_110A%3A_Physical_Chemistry__I/UCD_Chem_110A%3A_Physical_Chemistry_I_(Larsen)/Lectures/27%3A_Molecular_Orbitals_with_higher_Energy_Atomic_Orbitals_(Extra_Lecture))
They will naturally radiate that energy off in different ways. This means they give may off high energy UV or lower energy infrared. In the case of some metals, they are giving off visible light that you or I can see.
Edit: this is wrong, see the reply
Everything emits some kind of electromagnetic radiation based on its temperature. The hotter it is, the more energy it emits, and the higher the average frequency of the energy (this is known as black body radiation). Things at average temperatures on Earth’s surface emit energy that is mostly infrared (lower frequency than visible light). When things start to get up near 800-1000 degrees Celsius, the average frequency of the energy starts to enter the visible range, starting at red. As it gets hotter, it will get brighter and the average frequency shifts more toward yellow, then blue. The sun’s surface is around 5500-6000 degrees, and it’s that temperature that generates all that light. This type of energy emission is called incandescence, and it’s how incandescent light bulbs work. They pass a current through a filament causing it to get really hot (3000+ degrees) and so it emits light.
This isn’t just a feature of metals. However, many other materials will tend to under go chemical reactions destroying them before they get that hot.
Latest Answers