# Tag Info

### Can positrons attract electrons?

They attract each other and form a system completely analogous to a hydrogen atom, called positronium. This will then annihilate into at least two photons. The half-life time depends on whether the ...

### Can positrons attract electrons?

There is indeed an attractive force between a positron and electron, but this doesn't necessarily mean they will collide. For example there is an attractive force between the Earth and the Sun, but ...

### Can positrons attract electrons?

As per Coulomb law, $$|\mathbf {F} |=k_{\text{e}}{\frac {|q_{1}q_{2}|}{r^{2}}}$$ any charged particle $q_1$ affects any other charged particle $q_2$ (unless distance between them is infinity). So ...
Accepted

### Why isn't electric field null at the midpoint of a straight line connecting two opposite charges of same magnitude?

Your short circuit assumption is probably "attraction + repulsion = cancels out". But if you think more carefully, you notice that since attraction and repulsion come from opposite sides of ...
Accepted

### SR for Moving Electrons in Wire

You're completely correct to say in the reference frame of the electrons, the charge density of positive ions increases by a factor of $\gamma$. However if we're in the middle of the wire, there'll ...
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### Gauss' law in the presence of surface charges

There are two ways of explaining this. First is that if you're considering a charge density which is concentrated on a surface, then the electric field $\mathbf{E}$ does not satisfy the hypotheses of ...

### Can positrons attract electrons?

This is to answer your: If an attraction exists, can it also occur through a conductor? What are electrons and positrons? They are quantum mechanically defined elementary particles in the standard ...

### Can positrons attract electrons?

Yes, they absolutely do attract each other and annihilate upon collision. It's worth noting that they don't normally just float in space and drift slowly towards each other, positrons are usually ...
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### How can recombination lead to photon decoupling if scattering can still occur with neutral particles?

As a general remark before getting into more detail, you should keep in mind that the fact that a process can occur, is not sufficient to argue that it is relevant for determining equilibrium. One ...

### Which charges pushes exactly a charge inside a conductor to the surface and why does it prefer curved surface?

To understand this concept it is absolutely essential that you not think of the surface charges as some pre-existing fixed charge distribution pushing on an individual interior mobile charge. All of ...
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### How does current flow when two charged spheres are connected by a wire?

There will be charges on the wire, because if there were no charges on the wire and positive charges on the balls, then some charges would still want to go in the wire, so it wouldn't be an ...

### What are the conserved currents and charges in QFT - operator form of Noether currents?

Noether's theorem is the correspondence between conserved quantities in a physical system and symmetries. The original theorem concerns classical Lagrangian mechanics and is described by OP, but there ...
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### Quantization of Electric Charge and Cutting Spheres

Now, say that the charge on the sphere Q is 3e. What happens when we cut the sphere into two equal halves? What charge will each half hold? At the level of electrons the answer is : 2 on one half and ...
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### Relationship between volume and surface charge density in the general case

Sure, though if you want to be super strict, then $\rho$ shouldn't be written inside an integral. You should simply say $\langle\rho,\varphi\rangle:=\int_S\sigma\varphi\,da$, i.e the value of the ...

### Fault/Technicalities with poynting theorem

Poynting's theorem assumes that expressions such as $\mathbf j \cdot \mathbf E$ and $\int E^2 dV$ are meaningful. When there is charge concentrated to a line or to a point, this is not the case in the ...
1 vote
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### Average electrostatic field over a spherical volume due to a point charge inside

You can divide the space region of integration $V$ into two regions: a sphere centered at the point charge; the sphere is chosen small enough so that it is entirely in the region over which the ...
1 vote
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### Does charge always reside at the edge of a conductor's surface

The charges repel so they "want to" get as far from each other as possible. So they won't stay in the middle of the sheet but will distribute. A stable configuration is such that minimizes ...
1 vote
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### Discharging two capacitors in series

The rate of discharge of each capacitor has to be the same since for a series connection the current in each capacitor is the same. The C in the RC constant for the circuit is the equivalent series ...
1 vote

### Will the random movement of electrons affect the electric field of a negatively-charged solid conducting metal sphere?

The thermal motion of the electrons does not lead to macroscopic fluctuations like the one you are considering. It does however lead to Johnson-Nyquist noise.
1 vote
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### Energy stored in capacitor over time

The correct answer would be a quarter. It is very much like the energy stored in a spring is $$E = \frac{kx^2}{2}$$ Electrons repel each other. If you add electrons to a metal, the metal is charged. ...
1 vote
Accepted

### Distribution of Charges on a Conducting Cup

It is not strictly true that there is no charge on the inner surface. Note that as far as the field/charge is concerned, there is no abrubt transition between the outer surface and the inner surface, ...
1 vote
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### The multipole expansion of electrostatic potential and large distances

No. Yes. Simple as that. The multipole expansion is an asymptotic expansion where you need a small parameter to make sure that each higher-order term you add will be (much) smaller than the one ...
1 vote

### Can we convert momentum to coulombs in any simple sense?

Charge and momentum are separately conserved. So you cannot convert one into the other. However, in geometrized units, charge and momentum both have dimensions of length. So in that unit system they ...
1 vote
Accepted

### How to find the potential difference between two charged spheres?

If $a - b = c$ then it implies $b-a = -c$ so both of your propositions are equivalently correct.
1 vote

### Is the positive terminal of a Daniell cell positively charged electrostatically?

While the electrodes do become charged, the amount of charge is not a fixed amount like -0.5 C. The electrodes become charged until the electrical potential difference between the electrode and the ...
1 vote
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### Bounded charges density different from zero

As you stated: $\rho_b$ is "the density of all those charges that are part of a dipole, each of which is neutral". This means that the dipole as a whole is neutral. But there can still be ...
1 vote

### Applying Coulomb's law to find the field strength at a point which is not between the two charges involved

The vectorial sum of the two is the correct answer. $\frac{1}{4\pi \epsilon_0} \frac{3}{x^2} + \frac{1}{4\pi \epsilon_0} \frac{-4}{(2x)^2}$ = $\frac{1}{2\pi \epsilon_0 x^2}$
1 vote

### Do multiple current flows exists in a conductor? Does a slower current provide extra resistance?

There are two main contributions to electrical resistance, which are the scattering of electrons due to lattice vibrations (phonons) and scattering due to impurities. There is also electron-electron ...

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