So what causes electrical energy to turn into heat energy in a resistor, and the series current to decrease when resistance is present? I'll bet some of you think that the electrons bump, grind, scratch, and scrape along their path through the resistive material, and this causes the heat to form and the electrons to slow down. Perish the thought. Resistive heating is not a mechanical phenomena, so it is not a frictional mechanism. At the microscopic level, it is a quantum physics event involving speed distribution of conduction electrons, number of collisions with the ionic cores of the material, the average distance a electron travels before colliding with something, changes in the drift speed of the electrons, and a whole lot more. Moving the charge carriers (electrons in this case) in one direction cause more electron collisions to occur with the material lattice than would happen if no movement were present. This causes the electrons to lose some of their kinetic energy, which is transferred to the ionic core of the material lattice by the collisions. This makes the lattice vibrate faster, which by quantum theory, raises the temperature of the resistive material. If the voltage remains constant, the loss of electron kinetic energy causes a slower electron drift velocity, which in turn means less charge entering and leaving the resistor per unit time, so the current will be less. The charge flow response is almost instantaneous, and the charge flow per unit time (current) is decreased. That is why resistance decreases current and dissipates heat when current is present.

To summarize. Some of the electrons collide with the material lattice and transfer a part of their kinetic energy to the lattice, causing the resistance material to increase in temperature. The loss of kinetic energy of the electrons causes their drift velocity to decrease, thereby also decreasing the current. Ratch
Posted on 2003-07-03 22:55:50 by Ratch
Afternoon, Ratch.

So to summarise, you mean that the electrons bump, grind, scratch, and scrape along their path through the resistive material, and this causes the heat to form and the electrons to slow down.:grin:

Cheers,
Scronty
Posted on 2003-07-04 04:11:45 by Scronty
Scronty,

So to summarise, you mean that the electrons bump, grind, scratch, and scrape along their path through the resistive material, and this causes the heat to form and the electrons to slow down.


Only to bump (collide) in a quantum way, not the force x distance friction energy loss that a mechanical method would be. Ratch
Posted on 2003-07-04 05:14:49 by Ratch
Afternoon, Ratch.

So in layman-terms, it's still bumping.

However...
it's a quantum, and not a physical, bump?

That's quite interesting to know. I always assumed it was a physical (mechanical) event, since that's the closest example supplied by "teachers".

Cheers,
Scronty
Posted on 2003-07-04 05:59:55 by Scronty
Hi, Scronty!

It is both. The electron moves through the lattice. As it moves, it interacts with the quantum wave equations of all of the other electrons, those that are bound to atoms, and those that are unbound (these are the electrons that are flowing). Eventually, an electron will interact with another electron's field in such a way that it "feels" the full electrostatic repulsion and gets scattered (forced off its original path and onto another path) or captured. If captured, it may fall to a lower level and radiate photons or get loose again (ionization). Either way, the integrated kinetic energy of the flowing electrons gets reduced by the amount converted to heat.

Charles
Posted on 2003-07-05 22:09:18 by cdquarles
Scronty,

No no no, you cannot say 'bump, grind, scratch.' You must say 'collide with the material lattice and transfer a part of their kinetic energy to the lattice.'

The two statements are semanticalle equivalent, but the latter way makes you seem oh so much smarter, and gives you something to talk about at parties other then why you can't seem to ever get a girlfriend.
Posted on 2003-07-08 22:44:13 by Ernie
I always thought there was a microscopic toll booth in each resistor :?
Posted on 2004-10-03 10:51:17 by SpooK
what is a toll booth? :? dictionary.com couldn't help me :(
Posted on 2004-10-04 11:01:03 by lifewire
The toll is a charge/fee for passing through a gate. The booth is where a toll collector sits.
Posted on 2004-10-06 17:53:36 by tenkey