# Voltage explained by QM

1. Mar 31, 2015

### jaydnul

Say you take an open circuited loop (not connected back to itself) and measure its voltage relative to some external reference point. Then you start rotating this loop in a magnetic field. Depending on the power of your motor, the loop will continue to spin for a finite amount of time. After this, the voltage with respect to the external reference point is much greater than it was before we rotated it.

My question is how this potential energy is stored in the conductive loop. The overall charge of the loop did not change. Were the electrons bumped up to higher energy levels? If so , how does that translate to the movement of charge (current) when the circuit is closed?

Edit: Nvm, I realize where I am going wrong. When the coil is not rotating, there will be no induced emf. Although answering my own question has raised another one; does each nucleus of the conductor (copper for example) have the same number of electrons associated with its outer shell? Or can the density of electrons vary in the conductor?

Last edited: Mar 31, 2015
2. Mar 31, 2015

### Staff: Mentor

The charge density can change a tiny bit if you have a voltage difference, but unless you put a capacitor in the circuit this effect is negligible.

3. Apr 1, 2015

### jaydnul

What about if you connect a copper wire to the anode of a battery?

The anode of the battery has a considerable difference in charge density compared to the neutral wire, with a net negative charge. So if you connect the wire to the anode only, wouldnt that charge density spread across the whole wire (the battery would continue to output charge until the wire reached the same net charge as the anode was originally)?

4. Apr 1, 2015

### Staff: Mentor

Does it? How many femtocoulombs do you get from a few volts difference and a free wire somewhere?

5. Apr 1, 2015

### jaydnul

But the entire voltage of the battery is generated from this small difference in charge density, is it not?

6. Apr 2, 2015

### Staff: Mentor

I don't think "generated" is a useful concept here. It corresponds to. And those tiny charges are negligible for practical applications.
And a battery does not work like a capacitor.