# Tag Info

Accepted

### Purpose of Using Taylor Series and Multipole Expansion to Approximate Potential

What does the electric potential of a water molecule look like? Imagine a cartoon picture of a water molecule, in which the oxygen atom has charge $-2q$ and sits at the origin and the hydrogen atoms ...
• 70.3k
Accepted

### Is electric field inside a conductor really always zero?

The "nothing left to move" scenario is impossible with a metal: the electrostatic potential needed to deplete a metal is far beyond what is sufficient to destroy any experiment. It is, ...
• 21.8k

### Why do we say that electric potential energy is stored in the electric field?

It can be difficult to see why the electric field has to store energy when studying electrostatics alone. Electrodynamics provides the real motivation. As David Griffiths puts in his text Introduction ...
• 1,910

### Is it impossible to construct a Faraday cage that can block a *static* electric field?

First of all, a Faraday cage isolates the inside from fields that arise from outside. It does not work the other way around! In your example you seal a negative charge inside a cage and hope that this ...
• 1,305
Accepted

### How do charge carriers "know" how much voltage to use for work in a specific component?

This is communicated to the current through surface charges on the surface of conductors and at the interface between conductors of different conductivities. So, for example, consider a circuit ...
• 104k

### Is electric current actually the flow of electrical charge?

electrical current is "the flow of charges" The above is true. it seems to me that electrical current is indeed caused by the electric fields along the conductor The above is true as well....
• 414

### Why do we say that electric potential energy is stored in the electric field?

Here is a simple argument that I find suggestive ... The capacitance of an 'ideal' vacuum-spaced parallel plate capacitor (one for which the plate dimensions are much greater than the plate separation,...
• 36.1k

### Is electric field inside a conductor really always zero?

The macroscopic electric field is zero if and only if the conductivity of the medium is infinite. The microscopic electric field is not assumed to be zero but that has no direct relevance to the ...
• 19.9k

### How to handle divergences in Poisson's equation in the presence of a point charge?

Besides taking the electron to be a small ball of radius $r$ (and taking the limit $r\to 0$ if necessary after calculating the force), the other simple approach is to just not include the potential ...
• 13.8k
Accepted

### For a charged hollow sphere: why is the energy calculated from the electric field different to its total energy?

The electric field experienced by the surface charge is not $Q/4\pi\epsilon_0r^2$. That's the electric field just outside of the surface. The electric field inside the surface is zero. So what ...
• 7,459

### How do charge carriers "know" how much voltage to use for work in a specific component?

Once you accept circuit theory, then things must work as the theory describe. It is still a valid question to ask why is circuit theory true and why circuit theory is apparently non local. Given there ...
• 708
Accepted

### How to handle divergences in Poisson's equation in the presence of a point charge?

There is mathematically no problem with differentiating distributions like the $\delta$-distribution, you just need to use the notion of the distributional (or weak) derivative. The particular case of ...
• 127k

### Where does $4\pi$ come from in electromagnetism?

The point is not so much about the factor of $4\pi$ being in the force, but rather that there must be a factor of $4\pi$ between the force (i.e. "Coulomb's law") and divergence (i.e. "...
• 12.1k
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### Doubt regarding an assumption made in an example in Griffiths

There are two ways of justifying what Griffiths concludes. The first approach—which is the one he adopts—is to argue that there is no possible magnetic field consistent with the spherical symmetry. ...
• 16.4k

### Flow of electrons in wire

The answer depends on the level of approximation that you are confortable with. Are we discussing a pinball like model for electrons or a quantum mechanical model? Do we consider the electrons ...
• 5,638

### Purpose of Using Taylor Series and Multipole Expansion to Approximate Potential

Most math problems lack exact symbolic solutions. But sometimes, when you break a problem down into an infinite series of problems, the individual problems are more tractable. This is especially ...
• 21.8k

### Why decreasing the distance between a parallel plate capacitor increases the electric field? Wouldn't it remain the same? $\sigma/\epsilon_0$?

Two possibilities. 1 Charged capacitor not connected to anything else. Charge,$q$, and hence charge density, $\sigma = q/A$, cannot change. Electric field $E = \sigma/\epsilon_0 = V/d$ does not change....
• 98.2k

### What theorem Feynman is referring to?

From the blockquote you have provided, it seems that he is referring to the gradient theorem (fundamental theorem of calculus for line integrals). Say we have a scalar field $\psi$. The theorem says ...
• 2,550

### How do charge carriers "know" how much voltage to use for work in a specific component?

Anthropomorphizing the physics in this case has made your problem far weirder than necessary. The fact that you have different resistances means there is different current flow for a given voltage. It ...
• 3,252
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• 57.1k