# Electrical Resistance and chemistry

Can some one describe or explain what happens when too much current is passed through lets say a copper wire, I am looking for an explanation to do with physics and chemistry.

For instance we have all heard about electrical resitance and ohms law on calculating this resistance but what happens when we pass in to much current and the wire melts whats happening at that point?

Im looking for the correct physics of whats happening aswell as the chemistry, in chemistry you get taught about ionic and covalent bonding how electrons can shift the electron energy levels and bond matrials together via the outer electron energy levels trading or adding new electrons to the atom, are the free electrons in the copper lattice bouncing of the copper atoms and shifting the copper atoms electron energy levels at the melting point of copper when too much current is applied?

When I think of heating water to its boiling point I imagine how the water molecules are becoming extremely excited I am imagining the same for the copper wire but with the free electrons inside the copper latice and I am struggling with this as I doudt that the electrons have the capability to nock a copper atom? So it must be effecting the copper atoms energy level?

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Ever heard about pinch effect? –  Georg Sep 20 '12 at 16:01

## 1 Answer

A simple picture: The free electrons comprising the current collide with material impurities, lattice imperfections, and lattice vibrations (thermal motion which manifests as temperature), transferring energy to them and thereby increasing the vibrational energy (and temperature) (at a rate $P=I^2 R$). When the temperature reaches copper's melting point a phase transition occurs, and the solid turns to a liquid.

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Read about pinch effect! –  Georg Sep 20 '12 at 16:02
@Georg: I understand that very high currents can be pinched by their magnetic fields, but I don't think you need that effect to melt a wire. –  Art Brown Sep 20 '12 at 16:32
Hey that sounds good but you dont explain what the phase transition is or what is happening to the copper lattice at that specific point? –  Garrith Graham Sep 20 '12 at 20:10
@GarrithGraham: I can't say much beyond noting that at the melting point the lattice vibrations are sufficiently large to disrupt the lattice bonds. –  Art Brown Sep 20 '12 at 22:56