noob question!

[Gneiss]

what makes metal turn red and glow when it is hot?

[Mr Skeptic]

Thermal radiation. Things glow when they get hot. First in infrared, then red, then the "hotter" colors, and eventually white. I think for a metal it is blackbody radiation, which has a generic spectrum that doesn't really matter what the material is made of.

 

Other things that glow when hot: the sun, lightbulbs.

 

If you want to do a cool experiment, stick a piece of copper (like from an old wire) into a flame.

[Physicsfan]

But what makes the emit light when they are hot?

[Gneiss]

interesting! "white" being the hottest reminds me of a time my dad blew a leaf blower on a fire in our back yard to prove that adding oxygen to a fire makes it hotter. could you explain what process goes on in thermal radiation on an atomic level?

[PaulS1950]

Electrons jump to higher energy states when they get hot. Then they fall back and emit the electromagnetic wave we see as light. If you get it hot enough it will emit all kinds of electromagnetic waves - depending on the element involved.

[swansont]

Electrons jump to higher energy states when they get hot. Then they fall back and emit the electromagnetic wave we see as light. If you get it hot enough it will emit all kinds of electromagnetic waves - depending on the element involved.

 

This is true and is the source of the distinctive colors you get when burning the material, but not the source of the blackbody glow that changes with temperature.

 

When charges are accelerated they emit radiation (called bremsstrahlung). In a metal you have a significant number of free charges as well as vibrating atoms, and thermal agitation increases their energy. When they collide they have a spectrum of accelerations, so they give off a blackbody spectrum of radiation. At room/body temperature, it's peaked at about 10 microns. As the object heats up, this moves into the visible portion of the spectrum.

 

I have an IR camera (modified webcam) and once viewed a stove element heating up. You could see it on the camera, which has a cutoff of about 1.1 microns, before it started glowing in the visible.