# Electrons move

1. Aug 12, 2006

### nonstop

Hi everybody!

I wan't ask, what force makes electrons move? For example when electricity generator act, what force makes generators coil electricity?

(I'm sorry! My english is very bad and this is my first time when I write something here)

2. Aug 12, 2006

### HallsofIvy

Staff Emeritus
In a generator some external force (someone turning a crank, a gasoline motor, water falling) causes a coil to turn around a permanent magnet. That causes an alternating electric field which applies a force to the electrons.

3. Aug 12, 2006

### nonstop

You mean, when generators coil roll in magnetic field that makes alternating electric field in coil and this electric field give force to the electrons. OK! But what causes influence, do generator make AC (Alternating Current) or DC (Direct Current)?

4. Aug 12, 2006

### myself

Generators in general make alternating current through the method of electromagnetic induction. In most power plants they rotate a coil of wire through a static magnetic field. Through half the rotation of the coil of wire, the electricity flows one way, and through the other half of the rotation, electricity flows the other way.

5. Aug 12, 2006

### Janus

Staff Emeritus
They can make either. It depends on the how the commutators are arranged. In a DC generator, the comutators are semi-circular and the brushes alternate between the two, this is because as the coil turns through the field, for half the cycle the current flows one way for the other half, it flows the opposite, By having the brushes switch between commutators between half turns, you insure that the current coming out the leads stays the same polarity.

For an alternating current generator (or altenator) the commutators are complete circles and each brush maintains constant contact with just one commutator. Thus when the current direction changes in the coil, it also changes in the outgoing leads.

6. Aug 12, 2006

### nonstop

How magneticfield bring off free electrons move in generators coil? Normally generator coil material is copper and this have free electrons in this electron shell and electron flues be composed free electrons.

7. Aug 12, 2006

### rbj

from a classical physics POV, magnetic forces are fundamental (like God, they simply are and we don't go back farther to explain). however physicists are not satisfied with that and have since been able to explain the magnetic force in terms of the electrostatic force (you know, the opposite-signed charges attract, like-signed charges repel) and using Einstein's theory of Special Relativity (and leaving the basic electrostatic force as fundamental).

they still weren't satified with that and came up with a theory (called the "Standard Model") that explained from a common model, the strong and weak nuclear forces as well as the electromagnetic force. they have not yet been able to combine this with the only remaining "force" or action: gravity, although they (that is Einstein) came up with a pretty elegant theory explaining gravity called "General Relativity", but, except for maybe String Theory (or "M Theory" or whatever they're calling it now), i don't think that there has been any unification of GR with the SM. don't ask me about how any of this is done because i don't understand any of the detail. (there are those on PF that do, but i don't.)

Last edited: Aug 12, 2006
8. Aug 12, 2006

### nonstop

Are commutators devices, what change current direction? :uhh:

I mean if I want make my homemade generator model and it must be act DC or AC and i have a permanent magnets, some coil, iron stick and brushes. How do i make this commutators? I don't want make it, but it must be simplier understand in this way.

Last edited: Aug 12, 2006
9. Aug 12, 2006

### 3trQN

http://en.wikipedia.org/wiki/Electric_motor

The commutator is like a split slip ring i think, or two brushes that are in contact for $$\pi$$ rad, so you are effectivley supplying current to one side of the circuit then switching to supply the other, but at the same time the current polarity is reversed due to the rotation of the rotor, so you end up with a DC supply.

To build something similar you would need to have two halves of a split slip ring, with each connected to opposite sides of the circuit, and the rotor coil contacts on the rotor shaft make contact with the split slip ring?

ive never dealt with this subject before so i could be very worng...

Last edited: Aug 12, 2006
10. Aug 12, 2006

### Janus

Staff Emeritus
Here's a simple drawing of a DC generator with the major components marked.

#### Attached Files:

• ###### generator.gif
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11. Aug 14, 2006

### nonstop

If that is generator. Why it has not iron stick in the middle of coil , because if that coil is copper it dosen't influence with a permanent magnets? I don't know, or must be coil almost made iron.

OK! But this topic is no more treat Electron move. So I ask, how large force must be, if we wan't get one electron moving?

Last edited: Aug 14, 2006
12. Aug 14, 2006

### Staff: Mentor

The permanent magnets produce a magnetic field B. As the loop of wire rotates, the flux of B through the loop changes. From the loop's point of view, this induces an electric field around the loop, which causes the electrons to move.