Why do objects glow red/white when heated?



Why do objects glow red/white when heated?

In: Physics

When objects are heated you are transferring energy to the object. This energy wants to escape instantly and does such in the form of heat which radiates from the object causing it to feel hot, as well as light energy which radiates from the object causing it to glow.

It’s called incandescence, and it’s a result of visible light being emitted from the higher-energy state the matter is in at a higher temperature.

Something being hotter means that the atoms making it up vibrate faster. Since atoms are made up of positively and negatively charged particles, and the movement of these particles generates electric and magnetic fields. These fields in turn emit photons – which are essentially just packets of electromagnetic energy. When this energy has a frequency in the visible spectrum – the kind of EM radiation that we can see – you perceive this as a glow.

Things that aren’t very hot have lower energy, and hence glow red – red is the least energetic form of light. Things that are a lot hotter also emit the other, higher-energy forms of light, eventually glowing white when they have enough energy to emit all the frequencies we’re capable of seeing.

Edit: As an added fun fact, this is the same reason infrared cameras work. The radiation being emitted follows the exact same principle, but infrared is even less energetic than red light – infrared literally meaning ‘below red’. This to the point that even things at room temperature are hot enough to emit this kind of light – we can’t see it with our eyes, but specialized cameras can, and hotter things emit more infrared light than colder things.

That’s thermal radiation. All matter emit electromagnetic radiation (photon) depending on their temperature. The higher the temperature the smaller the wavelength of the radiation. So most of the stuff around you, including you, is in a temperature range that emit in infrared, so you don’t see it unless you look with an infrared camera. That’s how an infrared camera work, it detect the wavelength emitted by object, so if the wavelength is smaller it’s hotter, if the wavelength is bigger the object is colder. If the emit if hot like the heating element of your oven, then it emit in infrared, a little bit hotter like a fire and you will see it’s yellow in the middle where it’s hotter, but get orange and then red as you get further away from the source of the fire where it’s less hot.

You can see here the path of the thermal radiation and the color it will emit.