# If an electrical generator ran forever would it eventually run out of electrons?

1. Jun 22, 2011

### treehouse

Where do the electrons that electromagnetic induction mobilizes come from? If electrons are waves as the double-slit experiment demonstrates, couldn't they be generated just as mechanical and light waves are generated?

2. Jun 22, 2011

### DrChinese

Welcome to PhysicsForums, treehouse!

Electrons have mass and a few other properties which are conserved. That means you cannot just make them out of the blue. It's a zero sum game.

On the other hand, no electrons are consumed in the generation of electricity!

3. Jun 22, 2011

### treehouse

How do we know electrons have mass?

4. Jun 22, 2011

### SpectraCat

Qualitatively we know that they have mass because beams of electrons are deflected in magnetic or electric fields in a way that indicates that they have a certain ratio of mass to charge.

http://en.wikipedia.org/wiki/JJ_Tho...sure_the_mass_to_charge_ratio_of_cathode_rays
http://en.wikipedia.org/wiki/Millikan_oil_drop_experiment

Those two experiments measured first the mass to charge ratio of electrons (i.e. cathode rays), and then the charge on a single electron (Millikan). If you know those two things, then you know the mass of an electron.

5. Jun 22, 2011

### DrChinese

That's kind of a basic question, so I would ask you to look up the definition of mass. You may find it more beneficial to shift your questions to the General Physics forums rather than the Quantum area.

6. Jun 22, 2011

### Staff: Mentor

This thread has been moved to the General Physics forum since the answer doesn't have much to do with Quantum Physics.

An electrical generator (which uses electromagnetic induction) doesn't actually produce new electrons. The electrons are already in the circuit (wires, etc.) and the generator simply pushes them around. It's like a circular pipe full of water, with a pump inserted into the loop: the pump pushes the water around.

7. Jun 22, 2011

### treehouse

Oh right! Because the voltage pushes the electrons in the material used to construct the circuit it won't deplete the electrons in the material used the construct the generator because it doesn't actually put the electrons in the material used to construct the generator into the circuit - it just makes the electrons in the material used to construct the circuit move around in the circuit. Thanks jtbell.

I guess any electrons that leak can be generated from b- decay. The resulting proton can turn back into a neutron by b+ decay, so I don't see how DrChinese can argue for the conservation of mass.

8. Jun 22, 2011

### Drakkith

Staff Emeritus
The generation of particles with mass (AKA everything except for photons) cannot be achieved in a generator. That requires particle colliders or certain nuclear decays. The electrons in the conductor do not leak out, as there is no net charge anywhere on the conductor. If charges leaked out the conductor would become charged, thereby attracting charges back to itself. This is not the case. The electrons stay within the conductor itself the whole time.

9. Jun 22, 2011

### DrChinese

You might want to rethink that a bit. Generators don't produce a lot of beta decay (as in none). And beta decay doesn't involve a change in total energy anyway. Because of conservation. And if you ever saw a proton turn into a neutron, that would be quite remarkable as well.