32
votes
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 ...
- 21.7k
11
votes
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 ...
- 329k
5
votes
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 ...
- 7,192
5
votes
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 ...
- 7,105
4
votes
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 ...
- 2,051
3
votes
Accepted
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 ...
- 2,234
3
votes
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 ...
- 220k
3
votes
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 ...
- 5,763
2
votes
Accepted
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 ...
- 33k
2
votes
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 ...
- 64.1k
2
votes
Accepted
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 ...
- 548
2
votes
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 ...
- 3,379
2
votes
Accepted
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 ...
- 220k
2
votes
Accepted
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 ...
- 2,234
2
votes
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 ...
- 27.7k
1
vote
Accepted
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 ...
- 27.7k
1
vote
Accepted
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 ...
- 27.7k
1
vote
Accepted
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 ...
- 55.4k
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.
- 21.7k
1
vote
Accepted
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. ...
- 25.4k
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, ...
- 7,182
1
vote
Accepted
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 ...
- 726
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 ...
- 64.1k
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.
- 548
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 ...
- 64.1k
1
vote
Accepted
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 ...
- 6,812
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} $
= $\frac{1}{2\pi \epsilon_0 x^2}$
- 3,642
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 ...
- 2,428
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