Silly question about capacitors

[dieter]

Forest, that is most likely only the same like with batteries in series, double voltage, same current. As two caps in series are technically equal to doubling the gap between one cap's plates, it will reduce the Capacitance to 50%, but since the energy is the same, the voltage is forced to rise.
At least that's what I think, tho I might be rather unconcentrated and or confused ATM.


MarkE, they emit E/M Radiation ? How? RF? HV? But actually that's what I meant, losses trough radiation.


BTW. by "who said that" I meant "nobody said that", it's always tricky to translate sayings 1:1.

[MarkE]

Forest, no there is no energy gain.  Two capacitors in series is effectively just the previous case but charging both capacitors first.  No charge transfers and no energy is lost:

Original energy = 0.5*2*C1*Vcharge^2.  = C1*Vcharge^2.
Qtotal = 2*C1*Vcharge

Vseries = Qtotal/Cseries
Cseries = 0.5*C1

Eseries = 0.5*C*V^2 = 0.5*(0.5*C1)*(2*Vcharge)^2 = C1*Vcharge^2 = Original energy

[MarkE]

Forest, that is most likely only the same like with batteries in series, double voltage, same current. As two caps in series are technically equal to doubling the gap between one cap's plates, it will reduce the Capacitance to 50%, but since the energy is the same, the voltage is forced to rise.
At least that's what I think, tho I might be rather unconcentrated and or confused ATM.


MarkE, they emit E/M Radiation ? How? RF? HV? But actually that's what I meant, losses trough radiation.


BTW. by "who said that" I meant "nobody said that", it's always tricky to translate sayings 1:1.

Dieter anytime charge accelerates there is E/M radiation.  Connecting a full capacitor to an empty capacitor accelerates charge impeded only by the resistance and inductance.

[poynt99]

Dieter,

As Mark said, a tiny bit of energy is radiated at the moment you connect the two capacitors together. Turn on your AM/FM radio and you may in fact "hear" it.

However, most of the energy is dissipated (lost) in the combined resistance in the capacitors themselves, and the conductors between them.

If one could replace the connecting conductor with a pure inductance, there would be no energy loss at all during the transfer (assuming ideal capacitors).

[dieter]

Surrounded by scary formulas, I made more simple experiments. The two caps, empty, were connected in a loop, then gently heated to about 45 deg. C., then I doubled their capacitance by unconnecting them, still warm. Now one has 12 mvdc, the other -12mvdc charge.


Of course I don't think that the thousands of intelligent and educted scientists made a bad job so that I have to reveal the truth about caps after 10 Minutes of experiments  , it's just that science is very if not only profit-oriented, so certain aspects are never really examined. Example given the back emf is usually seen as a nasty, dangerous thing that needs to be eliminated, eg. by heat dissipation, instead of  harvesting it to save energy. After all, they want us to consume electricity since one reactor gives about 1/3 billion $ in a year.