# generators

Discussion in 'Physics' started by kiloman, Jul 12, 2010.

1. ### kiloman Thread Starter New Member

Sep 30, 2009
5
0
how do generators produce electricity? i mean i understand an external force rotates the bar magnet which induces a current, but where do the charges come from? like for example the generator from the power plant gives us power in our homes which we pull for personal use, but where do the charges that we use get replenished? are the electrons drawn from the air or something? what happens at the atomic level when mechanical energy is converted into electrical energy? im not getting the concept.

2. ### Ghar Active Member

Mar 8, 2010
655
73
All atoms are always filled with electrons. In a conductor some of the electrons can move rather easily between atoms.
The electrons just move back and forth with AC or in a complete loop with DC. "Charge conservation", meaning the only charges you have are the ones that are always there, is the reason that a DC circuit needs a closed loop.

3. ### kiloman Thread Starter New Member

Sep 30, 2009
5
0
so what youre saying is the electrons in the conductors dont get used up in lets say a computer or anything? the electrons just flow through pretty much? there is no replenishment of charge or any electrons added into the wires when mechanical energy is converted to electrical energy? all it does is just set off whatever electrons there are into motion?

4. ### Ghar Active Member

Mar 8, 2010
655
73
Yes, exactly.

The electrical energy is in the system of charges, fields, everything interacting together. The idea of electrons being 'buckets' of energy and dumping something at the load is false. In AC the same electrons will move back and forth across the load yet energy flow continues.

Mr. Beaty over here has some interesting rants on subjects like this:
http://amasci.com/miscon/eleca.html#electron
http://amasci.com/miscon/ener1.html

5. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
I would not take anything Mr. Beaty says as gospel. He is off in many ways.

The electrons move due to EMF (voltage being generated by the wires moving through magnetic field). It is the movement of the electrons that is the energy, not the electrons themselves. On that Gar and I agree. Generally they move in a circle, returning right back where they started, this is a circuit.

6. ### logicman112 Active Member

Dec 27, 2008
69
2
The generator electricity is AC and makes electrons move back and forth, electrons are not transferred from one side to the receivers permanently. Electromagnetic wave travels and its energy is being dissipated or stored in the receiver.

7. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
This is incorrect. An AC generator is not a transmitter, though a transmitter is a subclass of AC generator.

You have mixed up two entirely different aspects of physics that have some crossover.

The key thing about radio is the antenna, which is a form of transducer. A transducer can (but not always) converts two forms of energy into another. For receivers it converts electromagnetic waves into electrical current (which is not the same thing as electromagnetic radiation), other way around for transmitters. The antenna is the same in either case, but it must be tuned to the wavelength to work properly.

A very very small amount of house current (60 Hz and 50 Hz) does get radiated as a form of electromagnetic radiation, but this is a loss, and as such is to be avoided and reduced to the minimum.

Look up dipole, that being the most basic of antennas.

Last edited: Oct 5, 2010
8. ### logicman112 Active Member

Dec 27, 2008
69
2
I think you are mistaken!! In AC generator, electromagnetic waves propagates. But the circuit is a lumped-parameter circuit, the frequency is low(the wavelength is long).

The reason that you see a uniform AC current is that electromagnetic wave propagates so quickly and besides because the wavelength is long, different components of the circuit do not see any substantial changes in current.

AC generator is made up of some wires and finally it will be connected to a wire and circuit(a transmission line), when electrons move back and forth, they have acceleration and this produces a magnetic field plus electrical field from their charges, these two fields will make an electromagnetic wave which travels inside.

9. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Nope, besides being a HAM, I've been doing this for a very, very long time. EMF (electromotive force) is not EMR (electromagnetic radiation), they are two totally different things. One is the movement of electrons, the other is a balance of electric and magnetic fields 90° (perpendicular) to each other, and it's particle is the photon. Photons and electrons do shake hands, but not inside copper wires (unless it is configured as an antenna).

Look them up, you might learn something. Don't forget to include dipole antenna's.

Another example of a transducer is a speaker, it can convert electrical signals into electricity (as in microphone), and visa versa.

10. ### neonstrobe Member

May 15, 2009
13
1
Hi

WHenever there is a current flow in a wire, there is a "wave" of electrons. This is easily demonstrated with transmission cables and RF generators. A pulse of electricity will travel down the Tx cable and if the end impedance is not matched, will reflect. You can imagine this with a DC voltage applied to the wire: an increase in the number of electrons in the wire pushes the electrons down the wire along with the pulse.

In electrical circuits, this pulse and reflections occur so quickly that we normally do not see the reflections, because the wavelength is long for 50/60 Hz mains.

However, neither do we usually worry about propagating electromagnetic radiation from the wires, as this is generally quite low for mains/line voltage wires. This transmitted wave seems to get confused with the current flow sometimes.

We might care about the propagating fields from high voltage power cables where the fields are much greater ...

11. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
If you create a resonance in the wire, which is what an antenna does, you get radiation (photons). For 60 Hz the resonant length is around 1521 miles. Since this is pure loss it is undesirable, so the power companies try to suppress this insofar as they are able.

The link to the OP question is this is also energy, and can be measured in watts.

The actual speed of an electron in a wire is quite slow, inches per minute, as they bump around from atom to atom. The response to an EMF is almost light speed though, and there are a lot of electrons.

12. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,047
295
Hi Bill:

Sorry I haven't been on the forum much lately....been trying to get The Opus of Amateur Radio Knowledge and Lore ready for publication. Should be out before Christmas!

Eric

13. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
You've missed some good RF discussions.