Kevin's Watch

Here's the thread for people like me to ask questions whose answers are apparently so obvious that they don't bother printing them, yet I can't figure it out. For example:

A generator is something like a coil of wire spinning around a magnet. Right? When you do this, a stream of electrons is given off. Close enough?

My question is - Where do these electrons come from? The magnet? The coil of wire? How could it possibly happen? I know that some elements tend to give off electrons more easily than others. Held weakly in the upper shell, or something. But once an atom gives off an electron, it's positively charged, right? I wouldn't imagine it would be willing to give off another electron, so that atom is no longer part of the generator. So how long does it take for the system to run out of "expendable" electrons? Since I've never heard of that happening, I guess I'm wrong about everything I just said.

So where do these electrons come from???

Well, first off, metals have an unusual structure where electrons are free to move around between the different atoms - the forces involved keep them all evenly spread, so there's no charge gradient, but they still move from atom to atom in the structure.
When a DC voltage is applied across a metal, the movements of these eletctrons favours the direction of the positive charge. This would leave positively charged atoms behind, but the electrons are actually replaced by ones moving into the metal from a previous part of the circuit.

(I'll come back later and finish off - Electromagnetism lecture, would you believe it!)

Now, any charged particle has an electromagnetic field surrounding it. Any other charged object moving within the field has to do work against the field, or has work done on it by the field, because of the interacting fields of the different objects. Similarly, a magnetic field can interact with the field of a charged particle.
Say, for example, you fire an electron in a straight line between two opposite magnetic poles. Between the poles, magnetic field lines will run from the north to the south pole. When the electron passes through these lines, the interaction between its own electric field and the magnetic field will produced a force on the electron, causing its path to bend either upwards or downwards (depending on the relative motion of the fields).
Now say you replace the single electron with a metal wire. When the wire passes (lengthways) between the poles of the magnet, the magnetic field interacts with the fields of all electrons in that section of wire, producing a force in one direction - down the length of the wire. An electric current is induced. The faster the wire moves, the longer the section of wire in the field, and the stronger the field itself, the larger the current produced will be. A rotating magnet in a coil of wire, therefore, will produce a large current (as will a rotating coil in a magnetic field).

As for the electrons passing through the coil, the same principle I described above applies. The coil is in a circuit, and as electrons leave one part of the wire more are drawn in from the previous section of the wire (attracted by positive charge left), just as electrons ahead of the section are pushed forward (repulsion of like charges), so that electrons flow around the whole circuit constantly, rather than being moved from one end to the other.

Make sense? I've tried to explain as fully as I can without getting too complicated (although I'll admit I don't know anything about how a couple of these things happen).

I think maybe now I have a more thorough understanding of why I'm confused.

What I don't get is, as electrons actually leave the coil, moving on to make my television work, why doesn't the coil become more strongly positively charged all the time, eventually making it impossible for even more electrons to be removed?

(Kinda hilarious about you having to go to an electromagnetism lecture!! )

The electrons never leave the coil, they just move to a different part of the coil. It's like the water in a log flume, it keeps going down the drops, but they never have to add any more water in because they just reuse the same water again and again.

Nathan, I just read your sig!!!

What you just said is, to say the least, a revelation to me!!! So then...

Murrin wrote:When the electron passes through these lines, the interaction between its own electric field and the magnetic field will produced a force on the electron, causing its path to bend either upwards or downwards (depending on the relative motion of the fields).

........

Now say you replace the single electron with a metal wire. When the wire passes (lengthways) between the poles of the magnet, the magnetic field interacts with the fields of all electrons in that section of wire, producing a force in one direction - down the length of the wire. An electric current is induced.

Do I understand that the electric current is not the moving electrons, but the force that bends the path of the electrons? And this force is, what, syphoned out of the coil/circuit, and sent on its merry way?

Current is the rate of flow of charge, which is a property of the electron flow. The force is called the Electro-motive force, or EMF, and is the same as Voltage ("potential difference"). Once a voltage is induced, you have electricity flowing, so you just connect it up to the power grid and you're putting electricity in. Wherever there's a potential difference (voltage) charged particles (like electrons) will try to move, so if you just connect the wire to whatever it is you want to power it'll push the electrons around the circuit.

I certainly learned a few things so far! Thanks guys!

I guess I'm into tangents now.

Murrin wrote:Now, any charged particle has an electromagnetic field surrounding it.

What's that field made of? What is a magnetic field? Something reaches away from the source of the field, and a stronger magnet's field reaches farther than a weaker magnet's. But what's reaching? The electrons aren't jumping off of the magnet, taking their field with them, only to be drawn back, are they?

As far as I know, a field's just a field. There are probably some elementary particles that transmit fields (as gravitons do for gravity) but I don't know what they are.

I'll try and find out some more for myself and I'll attempt to translate what I learn into English when I have a bit more time.

[Virtual Particles are:
Graviton - Gravity*
Photon - Electromagnetism
Gluon - Strong nuclear force
W+/- & Z Boson - Weak nuclear force]

From my textbook:

In quantum electrodynamics, the electromagnetic field of a single charged particle is described by virtual photons that are continuously being emitted and reabsorbed by the particle. ...The photon is said to mediate the electromagnetic interaction.

[*Gravitons have not yet been observed]

Should I assume a "virtual" particle is not really a particle, but is called that because it's easier for us to think of things in terms of particles? Otherwise, my next two questions are:

1) What kind of machinery is inside an electron that manufactures virtual photons? Or is an electron composed of virtual photons (I had heard otherwise. Quarks?), and it can lose a certain number without any change to its nature/behavior?

2) When a metal heats up, it glows. Where do the photons that are emitted come from?

Nothing to contribute, but just wanted to say that I'm learning much too. Very interesting guys, thanks.

--A

Photons are made of pure energy. I'm sure you've heard of the famous e=mc² formula which means that matter and energy must be interchangeable.

The reason photons must exist is to do with the photoelectric effect.

Physicists determined that when light is shined on certain metals electrons are emitted, they also worked out that

[to be continued, just been kicked off school computer]

Continued:

Physicists determined that when light is shined on certain metals electrons are emitted, they also worked out the amount of light it should take to cause one electron to be released. But when they tried it in experiments, they found that electrons were instantly released every time. This, they surmised was because light comes in "packets" called photons rather than a continuous wave (but it's also a wave, as is everything else. see wave/particle duality)

As for heating up a metal, when electrons are given energy they are "excited" into a higher orbit of the nucleus of the atoms they surround, then they get rid of this energy by emitting photons, allowing them to fall back to their usual positions.

Photons are simply energy in the form of light.



As for quarks, they are the building blocks of nucleons (protons and neutrons. the particles in the nucleus of an atom).

Three quarks make up a nucleon, electrons are not made of quarks, they are themselves elementary particles, they can't be split smaller like nucleons can. They're in a group known as leptons.

[edit:I'm sure Murrin knows more about/could explain this better than me, hopefully he'll be back along to do that sometime.]

That's pretty much all I know about it too.
I'll just add some more about particle groupings:
- Hadrons (from the latin for 'heavy') is the collective term for the particles composed of quarks - Baryons and Mesons.
- Baryons include protons and neutrons and are composed of three quarks.
- The Mesons include Pions and Kaons, and are made of two quarks.
- Leptons are fundamental particles - that means they cannot be split into smaller parts. There are six leptons - the electron, electron neutrino, muon, muon neutrino, tau, and tau neutrino.

And the last bit of knowledge I have on the subject: The quarks are called up, down, strange, charmed, top, and bottom. The most commonly known particles are composed of just up and down quarks (which means my A-level covered little on strange quarks and nothing about the other three).


[I did the "Particles and Waves" module in A-level physics.]

Guys, this is awesome! Thanks SO much!!!

Nathan, it breaks my heart that you know so much about this stuff, but are so confused about free will.



*ducks for cover*

Nathan wrote:Photons are simply energy in the form of light.

I was wondering about this, because I remember (maybe not correctly) hearing that photons had mass. True, an amount of mass that is outrageously smaller than even the outrageously small mass of an electron, but mass, nonetheless. And I didn't know how the heated metal could afford to give up even that tiny mass without changing its own nature. Especially when many many photons are given off.

So now I'm thinking that photons do not have mass. Or, if even pure energy has some tiny mass, it all comes from the heat source.

Meh?

Hey, what about Trek's planet eater. It shot an anti-proton beam. Apparently, that's a serious thing!

I just KNEW quarks were going to come into this at some point.......

I just didn't forsee the planet eater!

Photons are massless, yes.

And an anti-proton beam? Hope you've got some good radiation shielding...

Bah. Anti-protons don't hurt the Haruchai any more than the Sunbane did.

You're right - I doubt annihilation on the sub-atomic scale would hurt that much at all, for the instant you're still alive.