# Tag Info

30

Charge does curve spacetime. The metric for a charged black hole is different to an uncharged black hole. Charged (non-spinning) black holes are described by the Reissner–Nordström metric. This has some fascinating features, including acting as a portal to other universes, though sadly these are unlikely to be physically relevant. There is some discussion of ...

19

Because it was defined by measurements (the force between to wire segments) that could be easily made in the laboratory at the time. The phrase is "operational definition", and it is the cause of many (most? all?) of the seemingly weird decision about fundamental units. It is why we define the second and the speed of light but derive the meter these days.

18

The up quark has a charge of $+2/3$, the down has a charge of $-1/3$. If you have a bound state of charged particles, the total charge is just the charge of the elementary constituents. The neutron consists of one up quark and two down quarks, so the total charge $Q$ is: $$Q = 2/3 + 2 \times (-1/3) = 0$$

17

It's not a mistake, and conventional current is not wrong or backwards. The labeling of one polarity of charge as "positive" and the other as "negative" is totally arbitrary. It could be done either way and everything would still work out the same. Franklin didn't choose wrong; he just chose. Labeling protons as negative and electrons as positive wouldn't ...

17

I would say that charge is a theoretical prescription describing a way of how a particle interacts with electromagnetic field. Since we are talking about a theory that should describe and predict various phenomena, we need to start with definition of fundamental object. If we are talking about Newtonian mechanics we face phenomena related to interactions of ...

16

Charge is a fundamental conserved property of particles. It is, if you like, a measure of how much a particle interacts with electromagnetic fields. A particle with charge can produce and be affected by electromagnetic fields. This is what we mean when we say a particle has charge. Its a simple quantised way to measure the coupling strength of particles with ...

12

Let me add two references to points already mentioned in this discussion: Today, there is no reason known why the electric charge has to be quantized. It is true that the quantization follows from the existence of magnetic monopoles and the consistency of the quantized electromagnetic field, which was shown first by Dirac, you'll find a very nice exposition ...

12

Massless charged particles can't exist in Nature because they would be easily produced by the colliders, and they haven't been. Such a production would simply arise from the Feynman diagram with an intermediate photon that "splits" into the new charged massless particle and its antiparticle. The cross section of this process would be calculable, and not ...

12

There's no problem in writing down a theory that contains massless charged particles. Simple $\mathcal{L} = \partial_{\mu} \phi \partial^{\mu} \phi^*$ for a complex field $\phi$ will do the job. You might run into problems with renormalization but I don't want to get into that here (mostly because there are better people here who can fill in the details if ...

12

The maximum charge a capacitor stores depends on the voltage $V_0$ you've used to charge it according to the formula: $$Q_0=CV_0$$ However, a real capacitor will only work for voltages up to the breakdown voltage of the dielectric medium in the capacitor. So in reality, for every capacitor there is a maximum possible charge $Q_{max}$ given by: $$... 11 At the particle level the verb "charge" has no definition. Charge cannot be added to a particle. A particle has charge ( noun); it is a quantum number that characterizes the particle, and its charge may be 0, +/-1/3, +/-2/3, +/-1 (and some resonances +/-2). A photon has charge 0, spin 1 and mass 0. That is why it is called a photon and not an ... 11 If you put your rod in a ultra high vacuum it will stay charged almost forever, but since you probably keep it exposed to air, this is where the electron excess slowly migrates (and the same for the electron defect in the silk). Since the charge exchange requires an hit between an air molecule and a spot of the rod where an electron excess is present, and ... 10 Charge comes from discrete symmetries and is countable and additive. Mass comes from continuous 4d space, is exchangeable with energy and, in quantum mechanical dimensions not linearly additive, thus not countable. Suppose you have an elementary quantum of mass, m_q. In the world we know two such quanta would not end up as 2m_q. One would add the ... 10 It seems you are contrasting the speed of propagation of current with the speed of the individual charge carriers. These two things are clearly separate. There are many examples. Consider sound. A fire cracker goes off at the other end of a football field from you. You hear the sound a few 100 ms later. The air molecules that were by the firecracker ... 10 I believe that the "roughly" term is applied because of the associated experimental error when measuring its charge. The same cannot be said to the electron because "we" decided to make the electron the reference charge. So, the reference charge is definitely -1. However the muon charge must be measured. According to this paper, Muon Mass and Charge ... 10 Gravitation couples to anything within the stress-energy tensor, as dictated by the field equations,$$R_{\mu\nu}-\frac{1}{2}g_{\mu\nu}R = 8\pi G T_{\mu\nu}$$Charge and angular momentum both affect the curvature of spacetime, as they affect the metric. For example, consider a spinning charged black hole, desribed by the Kerr-Newman metric, ... 9 Electric charge is just a measure of the strength of a particle's interaction with the electromagnetic field (i.e., photons). Particles don't obtain a charge from the the field. Saying that a particle has a given charge is the same as saying it interacts with the electromagnetic field with a certain strength. Just a shorthand way of saying it. The overall ... 9 James Clerk Maxwell thought about this one and showed the following. Suppose we have two concentric conducting spheres and we charge one up to a potential \Phi relative to some grounding plane. Then the voltage of the inner sphere relative to the same ground is:$$\Phi_{inner} = \Phi \,q\, ...

8

Dear asmailer, the reason is simple and completely understood: the electric charge is the generator of a $U(1)$ symmetry which is compact and may be parameterized by an angle, $\phi$. So wave functions may only depend on the angle $\phi$ in a periodic way, $\exp(iQ\phi)$ where $Q$ is integer (or an integer multiple of $e/3$, if I look at the elementary ...

8

Coulomb repulsion it is. Specifically, if a black hole has a lot of charge, then particles with a high charge-to-mass ratio will be repelled. Anything that falls in will contribute "more mass than charge," heuristically, keeping the charge-to-mass ratio of the black hole from getting too big.

8

Actually, mass and charge are only superficially similar. Yes, they both appear in inverse square force laws, namely Newton's law of gravitation and Coulomb's law of electrostatic force, but both of those are approximations. Coulomb's law ignores quantum effects, which is a very slight approximation, but Newton's law ignores all of relativity, which makes a ...

8

In fact, an electric charge at rest on the Earth's surface is accelerated and this actually poses a challenge to the idea that uniformly accelerated charge radiates. I believe this is still an open question. For example: One of the most familiar propositions of elementary classical electrodynamics is that "an accelerating charge radiates". In fact, ...

8

Imagine the field lines of a point charge - they all point outwards of the charge in a radial direction. Now consider the following statement: the change of the field does not propagate instantaneously, but it has to propagate through local interaction. When we nudge into the charge, a ripple in the field propagates to tell the other field lines "hey guys, ...

7

(Someone resurrected this oldie in the queue, so just to be a contrary voice...) Ben Franklin did get it wrong. He had just developed a remarkable new theory of electricity in which positive (+) and negative (-) had specific and accurate meanings, and he was unable to apply the two labels in the way he intended. In Franklin's time electricity was thought ...

7

There is a limit on how much charge a black hole may have: http://en.wikipedia.org/wiki/Extremal_black_hole In general, rotating, charged black holes is described by a Kerr-Newman metric. Intuitively, eventually the Coulumb repulsion is enough that a charged particle which does not contribute more mass than charge will be repelled.

7

In quantum field theory and its extensions including string theory, the electric charge is a generator of a $U(1)$ symmetry which should be promoted to a local symmetry i.e. gauge symmetry. In string theory, the $U(1)$ symmetry and the gauge field often appear as parts of the low-energy effective action. This could be enough to answer the question: we ...

7

Heavy clouds have condensed to the point of large droplet formation, failing the Rayleigh criterion for visible light and so no longer scatter them. It is a case of absorption being higher than reflection/scattering that causes clouds to look dark.

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To address John Rennie's comment in the comment section regarding the existence of a systematic, human-guess-independent algorithm for determining the LCM of a data series in the presence of significant experimental error and without the aid of single-electron-charged droplets to make a human-sensible guess: a = 12.5654; L = 400; list = Table[a ...

7

The names up and down don't refer to electric charge $Q$ but are rather references to isospin charge $I_3$.

7

When it comes to fundamental charges, the (left-handed) up-type quarks actually have either the same values of the charge as the down-type quarks, or exactly the opposite ones. It just happens that the electric charge isn't a fundamental charge in this sense. Let me be more specific. All the quarks carry a color – red, green, or blue – the charge of the ...

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