# Tag Info

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

### 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
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

### 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
Accepted

### Is Farady's law valid for conducting loop only?

Faraday's law is for a mathematical loop, even with nothing there.
• 1,104

### 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
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

### 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
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

• 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

Faraday's Law, for harmonically varying fields (time dependence $e^{i\omega t}$) in a linear medium is the equation (1.41a), $$\vec{\nabla}\times\vec{E}=-\frac{\partial\vec{B}}{\partial t}=-i\omega\... • 12.4k 1 vote ### Why does a {\bf B}-field follow a high \mu core in an electromagnet? Steady current flow and magnetostatics are entirely analogous and described by the exact same equations, with the following correspondences:$$ \vec J\text{ (current density)} \longleftrightarrow \vec ...
• 7,257

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