Just yesterday I was having an huge and heated argument with friend about what happens in conductor if temperature increases.

I was talking about it being obvious. The temperature rise means resistance rises. That is how the incandescent light bulb works (also the same reasons are why it burns out after a time).  At the same time Jaanus was taking measures at resistor when heating it with hot air soldering piece and got results that when temperature rises the resistance lowers. Since he had thought about that being normal (when electrons move faster it is easier to move them from one place to another) he saw that to be the normal case.

After at least half an hour of arguing he found out on the example of  thermistors there must be materials that have decreasing resistance when temperature increases.

In matter of fact, when he was doing he’s measurements he was using carbon resistor. And carbon, as we all know it, is a semiconductor.

The internals of carbon resistor.

The band structure of semiconductors is such that the outermost band of electrons, the valence band, is completely full.  If a voltage is applied, there is no conduction of electrons because there are no empty spaces to allow the electrons to move around.  In order for conduction to occur, electrons must be excited to the next highest band, known as the conduction band.  The conduction band is normally empty but is separated from the valence band by only a small amount of energy.  Valence electrons can surmount this barrier by absorbing a small amount of energy from heat or light.  This then creates a free electron in the conduction band and a hole (missing electron) in the valence band.

So in the case of any semiconductor material the conductivity increases with temperature. Goddamn, so I was wrong…

At the same time.

This is what exists in metal and why it usually is a good conductor.

A metal consists of a lattice of atoms, each with a shell of electrons. This is also known as a positive ionic lattice. The outer electrons are free to dissociate from their parent atoms and travel through the lattice, creating a ‘sea’ of electrons, making the metal a conductor. When an electrical potential difference is applied across the metal, the electrons drift from one end of the conductor to the other under the influence of the electric field.

Near room temperatures, the thermal motion of ions is the primary source of scattering of electrons (due to destructive interference of free electron waves on non-correlating potentials of ions), and is thus the prime cause of metal resistance. Imperfections of lattice also contribute into resistance, although their contribution in pure metals is negligible.

Basically higher temperature in any metal means larger resistance.

All in all we both were wrong and right at the same time.

Fuck you physics… Why do you always have to do this…


Best regards, Cmc


Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>