Talk:Electric charge

To do:

Charge and Noether's theorem, gauge theories.

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I removed this also, since amperes are based on coulombs, not the other way around: - Omegatron

One coulomb (6.24 x 10¹⁸ charge carriers) can be defined as the quantity of charge that has passed through the cross-section of a conductor carrying one ampere within one second.

Actually no. Last time I checked, the Ampere is considered the fundamental unit, the A in MKSA, with the coulomb being an Ampere-second. -- Decumanus | Talk 22:38, 30 Mar 2004 (UTC)

Hmm... But the coulomb is a specific number of elementary charges, which are certainly a fundamental unit... I guess this needs to be explained, regardless. - Omegatron

You're right. sorry. - Omegatron

No prob. It's certainly counterintuitive in some sense. -- Decumanus | Talk 22:52, 30 Mar 2004 (UTC)

Confusion: the NIST uses the word "fundamental" in an odd way. Certainly the Coulomb is the more fundamental concept, since an Ampere is a *flow* of a certain number of Coulombs per second (you can't have coulombs-per-second without coulombs!) But in NIST terms, "fundamental" refers to a primary, directly-measured calibration standard, versus "derived" standards which are not measured directly. At one time the Coulomb was the "fundamental" standard. IIRC, the Coulomb was measured as a deposition of a certain amount of silver in an electrochemical cell. But Amperes are far easier to measure accurately by measuring the magnetic force between adjacent parallel conductors. So today, the electric current is the "fundamental" standard, and the standard for charge is then derived from the high-precision standard Ampere, rather than being measured directly. - --Wjbeaty 06:28, Feb 17, 2005 (UTC)

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Contents

1 Removed for confusion 2 Removed for confusion and incompleteness 3 Conservation of Charge and Gauge invariance 4 What kind of variable is Q 5 more details about the experiment 6 different kinds of discharge

Removed for confusion

"Before that experiment, charge was ordered in anion at cation, a term introduced by Michael Faraday."

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Removed for confusion and incompleteness

Conservation of Charge and Gauge invariance

Since the action (what action? perhaps this should be a link to a rare definition of 'action'?) is invariant under gauge transformations (due to the masslessness of the photon), by Noether's theorem the (something) is a conserved quantity associated with it (with what?). Since the langrangian density is

<math>\mathcal{L} = - \frac{1}{4} \mathcal{F}^{ij} \mathcal{F}_{ij} + A_i J^i<math>

plus other terms that do not involve the electromagnetic interaction, (something). since the contribution to the action by the first term is trivially gauge invariant, we need consider only the second. Under a gauge transformation A_i->A_i+∂_iφ the action is increased by

<math>\int d^4x J^\mu \partial_\nu \phi = - \int d^4x \phi \partial_\mu J^\mu<math>

the only way for this to be satisfied for arbitary φ is if ∂_μJ^μ=0, which is the continuity equation

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anon comment:

Please can someone quickly and briefly explain how you create similar charges for two objects to repel (physically/practically rather than theoretically) Thank you in anticipation, a GCSE student

What kind of variable is Q

"Q is a measurement of the charge held by an object."

Q isn't a constant or a unit, and isn't used in an equation on this page. Is this equivalent to saying "l is a measurement of the length of an object"? - Omegatron 00:23, May 31, 2005 (UTC)

more details about the experiment

"This property has been experimentally verified by showing that the charge of one helium nucleus (two protons and two neutrons bound together in a nucleus and moving around at incredible speeds) is the same as two deuterium nuclei (one proton and one neutron bound together, but moving much more slowly than they would if they were in a helium nucleus)."

Which experiment was this? How is it done? - Omegatron 00:26, May 31, 2005 (UTC)

different kinds of discharge

See Talk:Spark_gap#Clarify the difference for some questions I have about the different kinds of discharge. - Omegatron 18:12, Jun 4, 2005 (UTC)