Re: Electrons

[Mark Sylvester <msylvest@SPIN.IT>]

At 16:32 19-04-99 -0400, David Abineri wrote:
> How do you folks answer the following high school student question?
>
> As electrons move through a circuit, say a battery and single resistor,
> energy is given up in the resistor as perhaps, heat or light. Now, what
> is different about these electrons after passing through the resistor
> compared with before they entered the resistor? They are not moving more
> slowly so it is not a kinetic energy situation so where does this heat
> come from?

I guess it has to be that the potential energy of the electrons in the
electric field in the conductor changes, and I fall back on a gravitational
analogy: a marble going round a track. There's a downward ramp where the
potential drops, i.e. through the resistor...


> I find it to be the ultimate question if one is to understand what is
> happening and I fumble around with the notion of falling through a
> potential difference but then we get hung up on a mass that falls
> through a height and the energy manifests itself as kinetic so the
> metaphor breaks down.

...but the ramp has a grid of nails knocked into it, and the marble keeps
hitting the nails, so it doesn't get to speed up, but emerges at the bottom
still going at the same speed after many collisions. You can't see very well
here where the energy finished up, but at least it's clear what's different
about the electrron afterwards: it's at a lower height, that's all.


> How do (would) you guys answer this to a high school student?

Maybe instead of nails knocked into the ramp we need a grid of little masses
mounted on springs. Then we could see the marble set them vibrating. Hey, it
might be worth building something like this!

Mark



Mark Sylvester
UWC of the Adriatic
34013 Duino TS
Italy
msylvest@spin.it