# Does an electrically charged surface maintain an excess charge if heated?

1. Mar 5, 2011

### uby

Suppose I were to take two conductors and connect one of each to the negative and positive terminals of a battery. After some time, the conductors should be at equilibrium with the voltage potentials of the battery (i.e. - one conductor should be at +V and the other at -V having developed by the net loss and gain of electrons, respectively). Removing the battery essentially forms a capacitor: each plate being charged and, when connected electrically, will discharge. However, if these plates are never connected electrically, they should in theory maintain their potentials forever.

Now, what if one were to heat these plates to a very high temperature (one at which significant blackbody radiation would occur, say above 2000C). Would these plates maintain their charge potentials?

Would it matter what atmosphere they were in? (i.e. - a perfect vacuum is perfectly insulating, vs. air which can be regarded as a dielectric)

Would it matter how they were heated? (i.e. - via radiative heat transfer vs. Joule heated via inductive coupling)

I'm just trying to figure out if a surface can maintain a charge applied at room temperature at high temperatures, and under what conditions the charge can be dissipated.

Thanks!

2. Mar 6, 2011

### Naty1

Electric charge consists of electrons and holes while thermal radiation consists of waves of energy or photons...so even though a hot body radiates it should still be charged....but at some temperature the extra thermal energy must begin to pump off, boil off the most excited electrons, ....I'm not sure about "holes"....

that's how a vacuum tube works: a current and negative charge is applied to a hot cathode and a positive anode at the other end of the vacuum tube attracts the electrons emitted from the hot cathode.

There MUST be some material breakdown with air or other impurities present...otherwise vacuum tubes and bulbs would not be evacuated....

Try reading this on vacuum tubes...lots of background explanation:
http://en.wikipedia.org/wiki/Vacuum_tube

3. Mar 6, 2011

### uby

thanks for your reply naty! this gives me a new avenue of directions to look into.

from my cursory review of the keywords you suggested, it appears that, even in the absence of a complete electrical circuit, electrons can boil off the surface if their thermal energy exceeds the binding energy due to electric potential and create an electron cloud near the surface - though of course, on the whole, no net change in charge will occur in the system.

my back of the envelope calculations regarding my intended application are interesting nonetheless. i'm sure there is a huge amount of literature on the subject to peruse. thanks again!

4. Mar 7, 2011

### Naty1

yes to the first part; but for the second part I'd guess thermal energy at some level COULD create a net charge.... just as an applied voltage potential can.