7

Data in magnetic storage media is stored by patterns of different magnetization directions. Writing occurs by subjecting them to a strong magnetic field that flips the magnetization direction to align with it, while reading happens using weaker fields (or optomagnetic effects). A very strong magnetic field across Earth would presumably change the orientation ...


7

In the standard model the $α=(g-2)/2$ of an elementary particle should be calculable , the calculations as accurate as the higher orders are computed. For the electron the calculations coincide with the experimental value to great accuracy The muon $α=(g-2)/2$ has different diagrams dominant so the theoretical value will be different, but it was seen ,...


5

Unfortunately the word “real” is a philosophical concept (part of the philosophical discipline of metaphysics). You really cannot avoid philosophy if you use the word. I avoid the word “real” for that reason and recommend others avoid it in a scientific discussion also. It is preferable to say what you mean explicitly. For example, some scientifically minded ...


4

These figures represent the root mean square background measurement noise per unit bandwidth, in other words if you had an ideal bandpass filter placed after the instrument whose bandwidth is B [Hz] around some frequency at which those specified figures are given, say, $\sigma [T/\sqrt {Hz}]$ then the output will have some additive fluctuation whose standard ...


4

To make up a concrete situation consider a horseshoe magnet and a charge moving between the poles. When you measure the force $\vec{F}$ acting on a charge $q$ moving through this magnetic field with various velocities $\vec{v}$ (e.g. in $+x$, $-x$, $+y$, $-y$, $+z$, $-z$ direction), then you get the following experimental results. Notice especially the $+$ ...


4

You already have $\tilde B_{ij} = \epsilon_{ijk}B^k \iff B^k = \frac{1}{2}\epsilon^{ijk}\tilde B_{ij}$ and similarly for $H$ and $\tilde H$. If the pseudovector components are related via $B^i = \mu^i_{\ \ j} H^j$, then the tensor components are related via $$\tilde B_{ij} = \epsilon_{ijk} B^k = \epsilon_{ijk} \mu^k_{\ \ \ell} H^\ell = \frac{1}{2}\epsilon_{...


3

The problem that you have is that your wire is infinite. If you apply the reasoning that you used to arrive at the result that the electric field lines always form closed loops to the currents, you would arrive at the requirement that currents should always form closed loops. Your current does not. Mathematically you are requiring the divergence of the ...


3

A finite segment of current by itself is inconsistent with Maxwell’s equations. Specifically, it violates the continuity equation. So you will not be able to find such a solution. You will either need to have the current go in a loop or have a changing charge density at either end of the wire. The changing charge density will produce a changing E field which ...


3

The drag is due to repulsion caused by eddy currents induced by the moving magnetic field in the Aluminum metal. The repulsive force opposes the motion of the metal ball according to Faraday's second law of electromagnetism. The same thing will happen if you replace the aluminum with copper metal.


3

Because the force experienced by the particle isn't just dependent on its location, either in magnitude or direction. The force depends on the particle location and it is perpendicular to its velocity. Thus if you change the velocity direction, the direction of the force changes. But if you want the magnetic field to be defined only as a function of position,...


3

A Nature paper was published on the same day, which seems to have attracted a lot less press. This presents a recalculation of the muon $g-2$ value, using standard model physics and their value is consistent with the new experimental value (Borsanyi et al. 2021). So there's one theoretical explanation of the result!


3

First, a DC motor can be made without permanent magnets. The permanent magnets on the rotor can be replaced with electromagnets. Then you have both electromagnets on the stator and the rotor. Second, a railgun's operation is not analogous to a DC motor. It is, however, analogous to an induction motor which also doesn't have magnets, just without the ...


3

Electrons accelerating in a magnetic field do emit electromagnetic radiation. It is known as synchrotron radiation or curvature radiation.


2

Yes there is a theory that explains the results ... the Standard Model. In other words, the claim is that the Standard Model already is consistent with the experimental data, and the original "prediction" was calculated wrong. Check out the paper published in Nature together with the muon g-2 results, or the writeup at popular level.


2

Kinetic energy of electrons due to electric current $I$ in an inductor is much smaller than magnetic energy $\frac{1}{2}LI^2$ (provided the inductor has large enough $L$, which is usually the case). So yes, strictly speaking total energy stored in the capacitor is transformed into magnetic energy and kinetic energy of current-carrying charges, but the latter ...


2

The zero is due to canceling the part from vector potential change and the scalar potential change in the electric field definition.


2

The convenient infinitesimal surface $\rm dS$ is shown in the Figure-01 : \begin{equation} \mathrm{dS} \boldsymbol{=}\mathrm{hdw}\boldsymbol{=} (2R\sin\theta)( \mathrm d\ell\sin\theta)\boldsymbol{=} (2R\sin\theta)( R\mathrm d\theta\sin\theta) \tag{01}\label{01} \end{equation} so \begin{equation} \mathrm{dS} \boldsymbol{=}2R^2\sin^2\theta\mathrm d\theta\...


2

You've come to a long time phyilosophical question: does a field actually "exist"? We cannot measure fields. There is no instrument able to measure a "field". The instrument you use to measure electric field is actually based on forces. The instrument detects an electric force and then it deduces the value of the $E$ field. In an empty ...


2

Parallel wires with currents in opposite directions repel each other due to the created magnetic fields. Your square loop has that case for opposite sides of the square. The forces on the loop due to its own magnetic field will try to convert the square loop to a circular loop due to that repulsion. Whether it can depends on the forces in place to hold ...


2

Only the charge matters for the effect of an uniform magnetic field on its velocity. We can think of a limit experience where there is a magnetic dipole and no charge. If we put a electric neutral magnet over a floating device on water, the effect of the (uniform) magnetic field from the Earth is only rotate it to align to the field. There is no attraction ...


2

As the charge has a magnetic moment, it will interact with the magnetic field. When the charge enters the uniform magnetic field, the direction of its velocity changes, while its inherent magnetic field (due to spin) starts to rotate. But the rotation itself doesn't change. This rotation (spin) is the same inside the magnetic field as before entering the ...


1

If the same flux, $\Phi$, passes through each turn of a coil, the Faraday's-Lenz law can be written $$\mathscr E=-N\frac{d\Phi}{dt}.$$ This can correctly be regarded as the sum of $N$ single turn emfs, $\mathscr E_1=-\frac{d\Phi}{dt}$, since these are in series. Since $N$ is a constant we can clearly re-arrange our first equation as $$\mathscr E=-\frac{d}{dt}...


1

As of March 9, 2021 switchbacks seem to still be an unsolved mystery. Alfven waves look like one possible explanation. Nasa's website has an article with a figure showing 5 theories that might explain switchbacks: https://www.nasa.gov/feature/goddard/2021/switchbacks-science-explaining-parker-solar-probe-s-magnetic-puzzle The figure says a thousand words and ...


1

The only strictly correct answer here is that there is one "right-hand-rule" (RHR) from which all others are to be derived. This is the rule for determining the direction of a cross-product of two vectors. The statement of this rule is that to find the directionality of $vec A\times \vec B$, you first point your finders in the direction of $\vec A$,...


1

In a right handed system with, B, in the, +z , direction, and, v, at the origin, and going in the, +x, direction, a positive charge will be deflected toward the, -y, direction. The center of the circle will be on the y axis at: y = -r.


1

Part of the energy will be used up in driving eddy currents (induced currents) in the coil, so the final energy of the magnet will not be $mgH$. The total energy of the magnet $+$ coil system will, however, be conserved. Exact calculations will require knowing the geometry of the coils, the material they are made out of, etc. and solving Maxwell's Equations.


1

I understand that EM waves are self-perpetuated due to the interactions between changing electric and magnetic fields as described by Maxwell's third and fourth equations, but I'm stuck conceptually on what they are if there are no electrons or conductors around. people were stuck like you begininning of the 20th century thinking the EM waves required a ...


1

In general, the relationship between $\vec{B}$ and $\vec{H}$ is nonlinear and history-dependent. The formula $$ \vec{B} = \mu_0 \mu_{rec} \vec{H} + \vec{B}_r $$ is an expedient approximation that often works well for rare-earth permanent magnet applications. It refers to the ‘major hysteresis loop’ which is the path followed when $\vec{H}$ cycles between ...


1

However, a moving charge experiences a magnetic force that is perpendicular the direction of its magnetic field and velocity. So my question is: why don’t we just define our magnetic field to be the vector field that is the direction (and magnitude) of the magnetic force that a particle experiences at a given location? Very subtle point. You see, the ...


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