# Tag Info

### In what direction would current flow in the coil?

The magnetic field on and near the axis decreases as you move away from a coil. As the second coil moves away from the first coil the flux through it would decrease. By Lenz's, law, ...
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### What is the meaning of $\vec H$ with respect to the total field?

Here the problem is that you are using too many notations and you are changing them constantly. The master equation in electrostatics : $$\vec{D}= \epsilon_0 \vec{E} + \vec{P}.$$ (i) $\vec{D}$ is ...
1 vote
Accepted

### Can Sagnac effect be observed in coiled, rotating electrical cables conducting electric signals?

My first thought was: yeah, you can have counterpropaging electic signals in a single cable, so I rather expected that in that type of setup a Sagnac effect can be elicited. I have a point of concern ...
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### Is Faraday's cage described in electrostatic 100% insulated?

Electrostatics problems do not consider cases where charges are moving. They are valid problems, but more complex. So you have one electrostatic problem. You add a charge and wait again for ...
• 36.3k
1 vote
Accepted

### In an electrostatic field with zero divergence everywhere, where is the charge located?

You can look at the required charge when your field is given by your formula in a finite domain $D$ and zero outside. Physically, this gives you a surface charge on the boundary $\partial D$ given by: ...
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### Why can't we calculate potential at a particular point due to an infinitely long thin wire with uniform positive linear charge density?

We can definitely calculate the electric potential, as long as we choose a valid (in this case, non-infinity) reference point with respect to which we measure the potential. The common choice in ...
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Accepted

### How current is induced when there is a change in external magnetic field?

If still charges in a wire loop do not respond to a (or have their own) magnetic field,… Electrons at rest (even in a wire loop) have their own magnetic field. Each electron is also a magnetic dipole....
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### Exact Definition of electrostatic field

You are correct, those conditions are not the same. $\nabla \times \vec{E} = 0$ does not necessarily imply that the field is electrostatic. The well-known example is induced electric field of ideal ...
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### Exact Definition of electrostatic field

Does a time-independent charge distribution necessarily imply an electrostatic situation? . The electrostatic field is a field such that it is static ,ie, time invariant. This implies a time ...
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### Why electric field is unaffected due to dielectric shell?

The fields of surface charges on the dielectric shell cancel. Think of the polarization in the dielectric shell as a charge $-q$ accumulated at radius $a$ and a charge $q$ accumulated at $b$. For ...
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1 vote
Accepted

### Definition of electrostatic field

You are correct in that an electrostatic field is a field E(r) that does not depend on time. You seem to be confused by the definition $$-\nabla \phi(r) = E(r)$$ Maybe it would help to contrast this ...
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### Why is AC current attractive and DC repulsive?

I think you may be referring to something like a person holding and unable to release an object they are grasping that becomes electrically live. In electric shock parlance this is sometimes referred ...
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### Increase of potential when charging a capacitor

So, both the electric fields of the capacitor and the battery point in the same direction, thus adding up a higher electric field within the capacitor. The electric field in a parallel plate ...
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### Electromagnetic waves produced from a sinusoidal current

The current density is concentrated in the $z$-axis $$\mathbf{J}(\mathbf{r},t)=I_0 \mathbf{e}_z \delta(x)\delta(y) \sin(\omega t)$$ where $\mathbf{e}_z$ is the unit vector in $z$ direction and $\delta$...
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1 vote

Here is the circuit when current has ceased to flow with some extra annotations. Let us take unit positive charge around the circuit $XY(Z)X$, $X\to Y$ : Work done by external force is $\... • 93.4k 0 votes ### Energy transfer with electromagnetic waves In order to better understand what happens in case of lighting a bulb I suggest that you ask yourself the question how does the water know where to flow out if there is a hole in the bottom of a ... • 101 0 votes Accepted ### What is the intuitive reason why Ampere's law is incorrect? The other answer already shows that Ampere's law and charge conservation in their differential forms $$\vec\nabla\times\vec{B}=\mu_0\vec{J}$$ $$-\frac{\partial \rho}{\partial t}=\vec{\nabla}\cdot\vec{... • 36.2k 2 votes ### What is the intuitive reason why Ampere's law is incorrect? It is a mathematical fact that the divergence of the curl of a vector field is always zero. I'm not sure whether one can give an "intuitive reason" for this or not, but it is in fact true. ... • 47.1k 4 votes Accepted ### Unconvincing sentence in wikipedia Ignore the word "static" in the first quote, or at least don't interpret it to mean "this only holds in the static case" in which all charges are stationary. The units of the ... • 6,935 1 vote ### Potentials of two near conductors For a sphere charged with a total charge ( Q ), the potential at a point located at a distance ( r > R ) (where ( R ) is the sphere's radius) from the sphere's center is given by ( \frac{kQ}{r} ). ... -1 votes Accepted ### A question about Coulomb's law for one moving and one stationary charge Yes. In the frame of the stationary charge Q, the electric field is:$$\mathbf E_Q = \frac{kQ\mathbf r}{r^3}$$The force at a (moving) test charge$q$is$\mathbf F = q\mathbf E$. But the inverse is ... • 15.8k 1 vote ### In a conductor responding to an external$E\$-field do the electron clouds just shift slightly or do the electrons fully dissociate to go to one side?

The density of free electrons in a metal is enormous compared to the charge imbalance induced by any field that won't destroy your laboratory. So, the "sea" of electrons in the metal is ...
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