Charge and Magnetism

[Crash]

Can someone please explain to me where atrraction or repulsion come from, i mean what fundamentally creates something of an electric charge? where does magnetism come from?

[5614]

magnetism is due to the angular momentum of electrons.

[Martin]

magnetism is due to the angular momentum of electrons.

 

hi 5614, are you familiar with the two parallel wires example of magnetism?

 

you are right that magnetism can have to do with the spin of electrons but it can also be much more primitive than that

 

two parallel wires carrying DC attract each other and will actually bow in towards each other

if the current is in the same direction

 

the effect in analysed as a special relativistic effect (nothing to do with spin) in volume 2 of the Berkeley Physics Series and probably other standard textbooks. Oh yes, Feynmann's Lectures has it, I think in volume 2.

 

If the current in the two wires is opposite, they repell and you can actually see them bow outwards away from each other.

 

the effect depends on how close the parallel wires are to each other and how much current.

 

In a certain sense COILS are just a way to put this long straight parallel wire picture into a compact space and reinforce it by having many many wires (each turn of the coil)

 

when this guy "Crash" says "Where does magnetism come from" we really should be able to explain to him where the force comes from that pulls two straight parallel wires together if they both carry DC current in the same direction.

 

that would be the basic step and then after that coils

and then after that any kind of coil-like circulation of current including

effective circulation in individual atoms caused by lining up the spins

[5614]

magnetic fields in wires are caused by moving charges (electrons flowing through the wire) these magnetic fields only act on other moving charges.

[Martin]

magnetic fields in wires are caused by moving charges (electrons flowing through the wire) these magnetic fields only act on other moving charges.

 

I agree

 

and straightline motion does it just as much as circulatory

 

oddly enough, magnetism is actually a relativistic correction on the electrostatic forcefield.

 

students used not to learn that until later, they just got taught the righthand rule and some ad hoc rules of magnetism

 

then Feynmann decided to derive magnetism as a relativistic effect for CalTech sophomores (the second year physics majors) and put it in his textbook and then Berkeley Physics Series followed suit.

 

I dont know if it is a good idea to get into that at a basic elementary level.

Maybe Feynmann was too ambitious in what he thought sophomores could learn. But I really like that approach. I wonder if it is available online.

[Crash]

Sorry maybe i worded it wrong, thanks for the posts anyway.

What i mean is yea moving charges create magnetism but what i want to know is what makes an electron negative? what makes a proton postive? what physical properties actually make something negative/positive or neutral?

[Martin]

.....

what i want to know is what makes an electron negative? what makes a proton postive? what physical properties actually make something negative/positive or neutral?

 

Ahhhhhhh! that is a really basic question!

Basically I have no clue.

Some physical theory provides a connection between the electric force and the socalled 'weak' force involved in beta decay

but as far as I know does not explain the existence of either

and there are conjectural (possibly halfbaked) attempts to connect the electroweak force with the strong force (the nuclear glue)

 

knowledge of the fundamentals is sketchy

protons have +1 charge because they are comprised of quarks

which have charges like +2/3 and +2/3 and -1/3

that just happen to add up to +1

 

but why do quarks have those charges? I dont know.

Electrons are elementary. not made of anything more basic.

they just happen to have -1 charge. Why do electrons have -1? I dont know.

 

 

Four forces are known: electric, weak, strong, gravity

each force has a kind of "charge" that determines what attracts what how much by that force. Maybe a unifying theory will someday reveal all forces to be be aspects of a single force and all charges to be facets of a single charge. But I do not know of any unifying theory that is more than daydream and wishful thinking of theorists. I think at the moment it is all speculation and conjecture.

 

And even when and if we get a unifying theory this will probably not answer your question of WHY there is charge and WHY there are these forces between things.

 

So I cant help you. maybe one of the other people here can

[Crash]

Cheers martin, nothing i dont already know though. Anyone? anyone at all? does anyone here have an intricate knowledge of anitmatter properties and T,C,P symmetrys. This is the only path to which i can think the awnser may be found...

[YT2095]

have a look here: http://www.moultonworld.pwp.blueyonder.co.uk/Lecture26_page.htm

 

in particular Figure. 26.10

 

alternatively, do a search for "Flemings left hand rule".

[swansont]

have a look here: http://www.moultonworld.pwp.blueyonder.co.uk/Lecture26_page.htm

 

in particular Figure. 26.10

 

alternatively' date=' do a search for "Flemings left hand rule".[/quote']

 

Or you could remember the right hand rule for cross products, since F= IL x B

[Crash]

Thanks for the help YT but i learned this in 7th form physics, this is moving charges etc. i want to know is what property makes the electron negative, ie why does electron have -1 charge and charm quarks have a +2/3 charge, bottom -1/3 etc, what makes them negative apart from the fact that they are.

[Martin]

Thanks for the help YT but i learned this in 7th form physics, this is moving charges etc. i want to know is what property makes the electron negative, ie why does electron have -1 charge and charm quarks have a +2/3 charge, bottom -1/3 etc, what makes them negative apart from the fact that they are.

 

Crash, do you think that a certain amount of the understanding you are looking for might come under the heading of Quantum Electrodynamics?

that is, if not the fractional charge business of quarks, at least an understanding of the charge on the electron, of the coupling constant (alpha) for QED and its dependence on energy or distance----the bare charge vs clothed charge business.

 

Have you studied QED at all? Maybe you are in a position to explain some rudimentary stuff to me. (rather than the reverse)

 

Let us try that. I'd be glad of any tutoring. what can you say about the physical intuition behind alpha (approx. 1/137)? what does the fine structure constant mean to you and what role does it play in the business of electric charge?

[Crash]

well what do you want to know? the coupling constant is just the measure of the strength of the electromagnetic force that controls how electrically chagred elementary particles (ie muon) interact with the photon. Currently, the value of SOMMERFIELD FINE STRUCTURE CONSTANT-> (alpha) having the smallest uncertainty comes from the comparison of the theoretical expression ae(theor) and the experimental expression ae of the electron magnetic moment ae