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Why have electron and proton same magnitude of charge?

by NeilWallace
Tags: charge, electron, magnitude, proton
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NeilWallace
#1
Jan26-11, 03:41 PM
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I know that energy is equivalent to mass and that a proton is many times more massive than an electron and yet the charges are equal in magnitude in both.

How is it the electron is able to match the protons charge with so much less mass? What is it about its configuration that enables it to have this equivalent 'force'. Is it that the proton has alot more 'lazy' energy in it?
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Drakkith
#2
Jan26-11, 04:19 PM
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Simple answer? It just does. I can't give you the complicated answer though, sorry.
cephron
#3
Jan26-11, 04:47 PM
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Hi NeilWallace, I think it would help to just consider mass and charge as being totally independent of each other. Consider a neutron - it's just as massive as a proton, and it has no charge at all! So, without even diving into quirks and quarks, the universe gives us little evidence to think that mass and charge should be linked. As for the complicated answer, I'm afraid I don't know it, so I can't help there either.

Drakkith
#4
Jan26-11, 04:49 PM
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Why have electron and proton same magnitude of charge?

This is similar to asking why does an electron have the rest mass that it does. Quite simply it just does lol. It's one of those fundementals that we just have to accept. (At least for now)
NeilWallace
#5
Jan26-11, 05:09 PM
P: 26
Thanks, i guess a better question for me is why has the neutron no charge and the proton a postive charge when their masses are the same (i think) That means they must be configured differently. And the difference in configuration causes the charge or not as the case may be. I guess I need to take a wander down quark street and learn up that stuff to get some insight.
K^2
#6
Jan26-11, 05:10 PM
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Keep in mind the fact that proton is a bound state of 3 valence quarks. It's not an elementary particle.

There are two main families of elementary fermions. Leptons and quarks. Within each family, there are 3 generations. Within each generation there are two flavors.

Electron is the member of the lightest generation of leptons. The two flavors within a generation have charges that are different by 1. Electron has charge -1. The other flavor in the same generation is the neutrino. It has charge of 0 and is extremely light.

The second generation of leptons contains muons and muon neutrinos. Muons, again, have charge of -1 and are 200 times heavier than electrons. Muon neutrinos are neutral and are also extremely light.

Finally, there are tau and tau neutrinos. A tau has the same charge as electron and is otherwise almost identical, except it is significantly heavier than a proton. Tau neturino, again, is almost massless.

Protons and neutrons consist out of lightest generation of quarks. Up quarks and down quarks. Up quarks have charge of +2/3 and down quarks -1/3. Again, difference is exactly 1, even though the actual numbers are fractions. Defining mass of the quark is difficult, because quarks never exist alone, but in any meaningful definition an up quark is slightly heavier than a down quark.

Because flavors of the quarks and leptons can change, any particle system collapses to the lightest possible constituents. However, charge must be preserved. This is why we are dealing with a world of protons, neutrons, electrons, neutrinos. Neutrinos mostly avoid detection, however.


Ok, now back to the question of charge and mass. There is definite contribution to the mass of the particle from its charge, but as you can plainly see, it's not the only contribution. Leptons with the same charge can differ in mass despite being far more similar than electron to proton. With composite particles, it's even more simple. Most of the proton's mass is in kinetic energy of the quarks and gluons that make it up.

A far more interesting question is why charge of both particles ends up being 1 despite them being so different. That goes back to the fact that within a generation, the charge can only change by 1. The answer to that is not completely understood yet. Super-symmetry attempted to tackle that, but unfortunately, it results in many predictions that are still not verified. All in all, it's an open question.

Edit: As far as proton and neutron. Proton is up, up, down quarks. Neutron is up, down, down. Because up and down quarks have similar masses, proton and neutron do too. There is also a configuration difference, as you point out, which results in proton being lighter than neutron, rather than the other way around, as you'd expect. Which is fortunate, because that's exactly the reason why hydrogen is dominant form of matter in the universe, and not neutron matter.
Drakkith
#7
Jan26-11, 05:14 PM
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K2, just wanted to say that an Up Quark is lighter than a Down Quark. Which is why the bare neutron decays into a proton. (As far as the information I've seen says)

=)
K^2
#8
Jan26-11, 05:29 PM
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Hm. For some reason I thought the current masses were other way around, but I just looked at the particle data booklet, and you are right. Down quarks are heavier. I must have been thinking top vs bottom quarks. Sorry about that.

The irony of it all is that I'm currently working with quark propagators in pions, so I really should have known this.
Drakkith
#9
Jan26-11, 06:03 PM
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Quote Quote by K^2 View Post
Hm. For some reason I thought the current masses were other way around, but I just looked at the particle data booklet, and you are right. Down quarks are heavier. I must have been thinking top vs bottom quarks. Sorry about that.

The irony of it all is that I'm currently working with quark propagators in pions, so I really should have known this.
What do you do for work exactly?
K^2
#10
Jan26-11, 06:05 PM
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I'm working towards a Ph.D. in theoretical particle physics. Most of it is working with RQFT.
Drakkith
#11
Jan26-11, 06:19 PM
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Sweet. I'm in the Air Force sitting at my desk right now lol. I man a computer and a radio and make sure people do what they are supposed to do with bombs and missiles. Take them to the right buildings/jets, track operations, stuff like that.
DrDu
#12
Jan27-11, 03:33 AM
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There's a similar thread in the High energy physics forum:

http://www.physicsforums.com/showthread.php?t=438917


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