Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: taregg on 16/08/2013 21:24:45

Title: why does electric wire produce light when its become very hot
Post by: taregg on 16/08/2013 21:24:45

explain to me from the electrons movements...

Title: Re: why does electric wire produce light when its become very hot
Post by: Phractality on 17/08/2013 04:25:13

There is no simple explanation. Einstein first explained it in 1905 after Planck and Lorentz failed.
Einstein on the photoelectric effect (http://www.aip.org/history/einstein/essay-photoelectric.htm), Adapted from David Cassidy's book,             Einstein and Our World. (http://www.prometheusbooks.com/catalog/book_1071.html)

Title: Re: why does electric wire produce light when its become very hot
Post by: evan_au on 17/08/2013 08:12:59

If electrons move through a superconductor (close to absolute zero), they pass through the metal without resistance. The metal does not heat up, and will not glow.

When electrons move through a "normal" conductor, they experience resistance, which dissipates power and heats up the wire.

Electrons subjected to an electric field will gain energy: 1 electron-volt (eV) of energy for every volt of potential difference. This energy shows as an increase in the velocity and momentum of the electron. As electrons move through the conductor, they collide with vibrating atoms and crystal imperfections in the wire. This transfers momentum to the atoms in the wire, causing them to vibrate more.  As the temperature rises, the resistance increases even more (for most metals (http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#In_metals)). Temperature is a measure of vibration, so an increase in vibration causes an increase in temperature of the wire.

Every object above absolute zero glows through blackbody radiation (http://en.wikipedia.org/wiki/Black-body_radiation). If the wire gets hot enough (well above 2000C), a useful percentage of this radiation will be in the visible spectrum, allowing production of an incandescent light bulb (http://en.wikipedia.org/wiki/Incandescent_light_bulb), now being progressively banned in a number of countries.

Title: Re: why does electric wire produce light when its become very hot
Post by: manu3d on 17/08/2013 23:14:38

I think one potentially important piece of information, related to the blackbody radiation, is the fact that electrons can acquire enough energy to jump to a new energy state. Electrons will then want to go back to lower energy states if possible. As they decay to a lower energy state they emit photons, in the case of an incandescent filament, photons of visible light. I don't know if this was the focus of your question but I thought I'd add this aspect to evan_au's answer.

Ciao!

Manu