6
votes
Accepted
Why is magnetism used to refer to two seemingly distinct phenomena?
Magnetic field as a relativistic effect
Unfortunately, the Veritasium videos contain some truth but follow a misleading teaching tradition, going back to Purcell's book on Electromagnetism, which ...
- 23.3k
5
votes
What does the $B$ field refer to?
$B$ is the magnetic field. In the Lorentz force law $\vec{F}=q(\vec{E} + \vec{v}\times \vec{B})$, which tells you how charges respond to electric and magnetic fields, the field that appears is $B$, ...
- 33.2k
5
votes
Accepted
At which point is the magnetic field in a current carrying loop the strongest?
As a rough estimate for the behaviour, I have plotted a graph.
Taking a slice of the loop, the field from the left and right current elements fall off like 1/r^2, here I have modelled the graph such ...
- 3,696
4
votes
At which point is the magnetic field in a current carrying loop the strongest?
The magnetic flux on an electric current wire loop is the same case of that of a straight wire magnetic concentric rings around the wire. The only difference is that if we make a loop with the ...
- 2,984
4
votes
Accepted
Is Farady's law valid for conducting loop only?
Faraday's law is for a mathematical loop, even with nothing there.
- 1,104
3
votes
Torque due to magnetic field
$\overrightarrow{\tau} = \overrightarrow{M} X \overrightarrow{B}$ is valid only in uniform magnetic field. Any point can be taken as origin and torque will be same.
To prove it, first of all prove it ...
- 415
2
votes
Accepted
How is the solar magnetic field produced?
The Sun is mostly made of an ionized gas called a plasma. The source of a magnetic field is the motion of charged particles (in the simplest scenario). If you imagine the Sun is a roiling sphere of ...
- 14.3k
2
votes
Derivation of $~\nabla^2\mathbf{H}=\sigma\mu{\partial\mathbf{H}\over\partial\mathrm{t}}+\epsilon\mu{\partial^2\mathbf{H}\over\partial\mathrm{t^2}}~$
I don't know where you've seen this, but that source is wrong. This is the equation in a conducting medium, which means you have current
$$
\vec j = \sigma \vec E
$$
(Ohm's law) so no vacuum. ...
- 1,145
2
votes
Accepted
Why doesn't the EM field above the center of a charged current loop look like a bivector?
First remark, the fields are along $z$ only when you stay on the axis due to symmetry considerations. In general however, the magnetic field will curve around the loop and the electric field will ...
- 1,145
1
vote
Do electric fences such as those typically used to fence cattle generate magnetic fields?
An electric fence is powered by a supply circuit which produces a high-voltage output which is fed to the fence wire. The current accompanying the high voltage is limited by that circuit to a low ...
- 72.5k
1
vote
What does the $B$ field refer to?
Consider the expression for Gauss law $\nabla\cdot\vec{D} = \rho_f$. Evidently, $\vec{D}$ depend on free charges. But in the laboratory, we can usually control only the total charge. As a result, $\...
- 2,004
1
vote
Does a change in electric field cause a change in magnetic field, or do both just always happen together?
You are correct within the variant of EM theory where all fields are retarded, i.e. they are mathematically determined by state of some accelerated charge somewhere sometime in the past.
However, ...
- 27.8k
1
vote
Accepted
Would a ring magnet around a copper tube be slowed?
In a word, yes.
Eddy currents are induced in conductors exposed to changing magnetic fields. Those currents specifically counter the change in magnetic flux the conductor is experiencing. That's Lentz'...
- 282
1
vote
Accepted
Biot-Savart's law in magnetic medium
If your medium is isotropic, homogeneous, time independent, and fills all space then yes it would be valid. Note that if the last assumption falls (which is most often the case), you can have problems ...
- 1,145
1
vote
Is Farady's law valid for conducting loop only?
You can apply Faradays law for any loop as long as it is complete
1
vote
Accepted
Derivation of $~\nabla^2\mathbf{H}=\sigma\mu{\partial\mathbf{H}\over\partial\mathrm{t}}+\epsilon\mu{\partial^2\mathbf{H}\over\partial\mathrm{t^2}}~$
$\nabla × \vec{B} = \mu (\sigma \vec{E}) + \mu \epsilon \frac{\partial \vec{E}
}{\partial t} $
Take the curl and sub gauss law for magnetism
$-\nabla^2 \vec{B} = \mu \sigma \nabla × \vec{E} + \mu \...
- 3,696
1
vote
How are the Bloch equations non-linear?
First, let me note that the equations given in the OP are not the full Bloch equations, which usually include the relaxation terms with characteristic times $T_1$ and $T_2$ for the longitudinal and ...
- 37.1k
1
vote
Accepted
How are the Bloch equations non-linear?
The non linearities arise when you consider the feedback loop. The magnetic moment can generate a field of its own. $\mathbf{B}$ will no longer be the externally applied field, but will rather depend ...
- 1,145
1
vote
Accepted
Using "Maxwell's curl equations" to get $H_y = \dfrac{j}{\omega \mu} \dfrac{\partial{E_x}}{\partial{z}} = \dfrac{1}{\eta}(E^+ e^{-jkz} - E^- e^{jkz})$
Faraday's Law, for harmonically varying fields (time dependence $e^{i\omega t}$) in a linear medium is the equation (1.41a),
$$\vec{\nabla}\times\vec{E}=-\frac{\partial\vec{B}}{\partial t}=-i\omega\...
Buzz♦
- 12.4k
1
vote
Why does a ${\bf B}$-field follow a high $\mu$ core in an electromagnet?
Steady current flow and magnetostatics are entirely analogous and described by the exact same equations, with the following correspondences:
$$ \vec J\text{ (current density)} \longleftrightarrow \vec ...
- 7,257
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