All Questions
Tagged with electromagnetismelectric-current
1,016 questions
2votes
3answers
83views
Why do we take the RMS when talking about the effective voltage of AC instead of taking the mean of $|V(x)|$?
When we talk about the effective voltage of AC, we take the Root-Mean-Square, which ends up being $V_{peak} / \sqrt{2}$ for sine wave energy supplies. Why do we not just take the average value of the ...
- 23
2votes
1answer
68views
Mathematical incongruency on integral form of Lorentz force law
I'm a physics student. I'm currently taking an introductory course on electromagnetism. My book (Corrado Mencuccini - Vittorio Silvestrini, electromagnetism and optics, I've translated the title from ...
- 569
0votes
0answers
173views
Calculating instantaneous current in an AC carrying wire from magnetic field strength using the Ampere-Maxwell equation
I'd like to find an expression for the instantaneous current in an alternating current carrying wire. I've attempted this as below but I'm suspicious of my result. I'd like to know where I may have ...
- 13
1vote
2answers
139views
How to prove that transmission lines carry equal and opposite currents?
You always hear that, in a two-conductor TEM transmission line, the currents in each conductor are equal and opposite. I'd like to prove this, and I made an attempt (below). We'll assume an asymmetric ...
- 1,113
3votes
2answers
206views
Can electrons move near light speed on a superconductor?
We know that the resistance is exactly zero in a superconductor. Therefore, it seems that electrons can move very fast onto the surface of a superconductor since the drift velocity is admissible to ...
- 2,774
1vote
2answers
77views
Why is the line integral of $\vec{B}$ along an Amperian loop zero for a wire outside?
I am struggling to understand why we only take the enclosed $I$ into account when using Ampere's Law. I've looked it up online but haven't found any answer that satisfies me at all. Can anyone please ...
- 15
2votes
1answer
29views
What is the magnetic moment of a moving current loop as measured in the lab frame?
For a square loop of current-carrying ($I_0$) wire with a side $L_0$, I am aware that the magnetic dipole moment may be computed as $\mu_0=I_0A_0=I_0L_0^2$. The question is how the lab observer ...
- 2,774
4votes
1answer
320views
Surface Current Density Definition 5.22 and 5.23 are not Equivalent in Griffith Introduction to Electrodynamics
Hi everyone I am having some difficulty in understanding surface current density. I have check other similar post and did not find a similar question to mine. In the magnetostatics chapter of ...
0votes
0answers
29views
Cause of power surge when appliances are not switched off before power restoration
We are told that we should switch off electronic devices before the power is restored after a power outage because of possible damage due to power surge. But I do not understand where is the power ...
- 101
0votes
0answers
26views
Faraday disc voltage multiplication/current path
Imagine we had two faraday discs , the B fields through each are reversed so that current runs in series (center to rim in one disc, rim to center in the other), current is collected with axial slip ...
- 101
0votes
0answers
122views
Is Ohm's law incompatible with Maxwell's equations and the continuity equation?
Every electromagnetic system should be uniquely determined by Maxwell's laws and the continuity equation, so in order to use Ohm's equation $\vec{J}=\sigma \vec{E}$ should I remove one Maxwell ...
1vote
1answer
40views
Dynamic $E$ field line angle with respect to charged surface
Imagine a situation. There is a large conducting plate that is much longer than it is wide. Then there is a small plate , both are charged, the small plate is moved around keeping the separation ...
- 101
2votes
1answer
103views
Is drift velocity function of a point or of a region?
Is Drift velocity defined at a point of a conductor or it is defined for a region of a conductor? Please help, and try to use simplified language since I'm only in highschool, so might not be fluent ...
- 190
0votes
0answers
26views
Doubts over "Thomson theorem for Magnetostatics" (Miguel Fiolhais and Hanno Essen paper)
I was reading the paper "Magnetic Field Expulsion in Perfect Conductors | The Magnetic Equivalent of Thomson's Theorem" by Miguel C. N. Fiolhais and Hanno Essen (easily findable online). In ...
3votes
3answers
189views
Conservation of magnetic flux in a perfectly conducting circuit with variable inductance (e.g. solenoid of variable cross section)
As a specific example of such a circuit, consider an infinite solenoid made of perfectly conducting material (no electrical resistance) with the following cross-section: Let us suppose that there is ...
- 151
