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Results tagged with electromagnetism
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user 31895
The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.
1
vote
Will the way you make a coil affect magnetic induction?
The coiling has to be systematic to increase the induction effects. If you just bend the wires in random way, most of the induction from one part will cancel induction from the other part. To obtain i …
- 41.2k
1
vote
Accepted
Force on a magnet in a magnetic field
In particular i was wondering if the force on the magnet is directly proportional to the magnetic field produced by the wire.
If the magnet is far away from the wire, the force on the magnet can …
- 41.2k
0
votes
Does a change in electron's direction affect direction of force?
The external force on the current carrying charges in the wire is approximately given by
$$
\int \rho\mathbf E_{ext} + \mathbf j\times \mathbf B_{ext}\,d^3\mathbf x.
$$
where the $\mathbf E_{ext}, \m …
- 41.2k
1
vote
Moving conducting bar in (changing) magnetic field
(my original answer was wrong - I misunderstood the assignment.)
What the problem was trying to demonstrate is that in quasi-static (slow) changes of field around circuits with negligible resistance, …
- 41.2k
0
votes
Is the concept of a field necessary to electrodynamics?
What exactly is meant here? Since fields physically exist, why is this permissible?
What is meant is that if fields satisfy some simple boundary condition, for example, if they are all retarded, …
- 41.2k
0
votes
Accepted
induced emf when a wire or coil travel through a magnetic field
You're almost right. The induced electromotive force due to external magnetic field is proportional to rate of change of magnetic flux through the circuit. In case of the coil moving in a uniform fiel …
- 41.2k
0
votes
Why is Griffiths ignoring the bounded surface current caused by the magnetization of the cyl...
The relation
$$
\mathbf B = \mu_0(\mathbf H + \mathbf M)
$$
is general, it is valid both inside body, outside the body (in vacuum), and also at the boundary of the two.
Outside the body magnetization …
- 41.2k
1
vote
Are Ampere's circuital law and Biot-Savart Law exactly equivalent?
Neither Ampere's law nor Biot-Savart's law include anything about boundary condition for $\mathbf B$. In that respect they are the same.
But the Biot-Savart law is more general because it is valid eve …
- 41.2k
1
vote
What does it mean for a "field" to rotate?
Yes, if the two points are close enough to each other, as in a sample in MRI machine, they experience the same kind of rotating magnetic field, with the same frequency and phase. Rotating field means …
- 41.2k
0
votes
Link between energy per unit frequency and derivative of the energy in regard of frequency
The derivative is meant to denote the fraction (energy of waves in the interval $[\omega,\omega+\Delta \omega]$)/($\Delta \omega$). Usually $\Delta \omega$ is considered to small enough that $u$ is al …
- 41.2k
1
vote
Accepted
Is it conductors in magnetic fields or repulsion of poles that provides torque in BLDC motor?
They are different ways to explain the same effect. The explanation using the repulsion/attraction of magnetic poles is a simplification of the more detailed description in terms of all charges in the …
- 41.2k
0
votes
Accepted
Intrinsic polarity of a currentless coil
Is there a convention for right handed coil being North at top and vice versa in a helically wound coil ?
No, there can't be such a convention, because how would we determine which end of the two …
- 41.2k
0
votes
Faraday Law - Related question
I'm assuming the current in the coil is changing in time.
In the second case with the source of electromotive force (coil) near the measurement circuit, the voltmeter is unable to measure voltage (wh …
- 41.2k
0
votes
Force to extend a solenoid
A solenoid under current indeed experiences tension that acts to expand its radius ("so called magnetic pressure"). This is due to magnetic (Ampere) forces between axially opposed wire elements carryi …
- 41.2k
1
vote
Electromagnet with multiple layers of wire
Each turn of the wire centered at the same position contributes roughly the same (there is slight difference due to the fact that additional turns at the same position will have slightly larger radius …
- 41.2k