Re: source of electrons

[William Beaty <billb@ESKIMO.COM>]

On Tue, 8 Jan 2002, Larry Smith wrote:

> How would you answer the question a student wrote to me today: "Where does
> an electron gun in a TV get an unlimited supply of electrons?"

Might he be using the incorrect "empty pipes" analogy for electric
circuits? This is the one where the wires contain no mobile charges, and
the charges are supplied by a power supply.  If we know that the electron
gun (and all the wires) contain thousands of coulombs of electrons, while
the gun emits particles at a very low rate, then the source of electrons
is obvious.

Or is he asking why the gun doesn't eventually become positively charged,
and why the CRT screen doesn't eventually become negatively charged?  This
is easy: the inside of the CRT has a conductive coating which connects the
electron beam impact point to the rest of the circuit.


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