# Heating in a Superconducting Circuit

Q:
When battery is connected to a capacitor, half of energy appears as heat. If super conductor is used then ?
- Kevin (age 16)
A:
That's a very nice question.

It's easy to calculate that, as you say, if a battery is hooked up to a capacitor via a resistive wire, just as much energy goes into heating the wire as into charging the capacitor. A superconducting wire doesn't generate heat. So what happens then?

The battery itself can't be superconducting. It has some internal resistance. So I think what happens is just that the heat is generated inside the battery.

That raises another question. What if you used a purely superconducting circuit? For example, you could have a large capacitor made of a superconductor and use it to charge a small capacitor made of the superconductor, connected by superconducting wires. In this case, the combination of the capacitance and the inductance of the wires would make a circuit in which current would oscillate back and forth. Those oscillations would send off electromagnetic waves. Gradually, the circuit would settle down to have equal voltages on the capacitors. The energy lost from the big capacitor would partly go to charging the small capacitor and partly to those waves.

Mike W.

(published on 07/10/2012)

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