# Tagged Questions

The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

2answers
6k views

0answers
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### Type of motion when a long wire carrying current is inserted between two wires carrying current is moved normal to its length [on hold]

Two long rigid wires separated by a distance d and placed parallel, carry current I in the same direction. Determine the force developed . Now a third wire is placed in between the rigid wires keeping ...
0answers
30 views

### How do I determine the information needed to design a solenoid electromagnet that can ionize a gas? [on hold]

I have been trying to answer this question for a long time. I watched a video where a person used a solenoid to heat up aluminum till it became a liquid. I want to apply this, to a gas. I want take ...
2answers
4k views

### How come Wifi signals can go through walls, and bodies, by kitchen-microwaves only penetrate a few centimeters through absorbing surfaces?

The only difference that I know of between Kitchen Microwaves and Wifi signals is how much power is pumped through them. Why is it that Wifi signals, being 1000 times weaker can travel so much ...
1answer
37 views

### Correct Definition of Angular Momentum of a Charged Particle in an Electromagnetic Field? (Classical Mechanics) [duplicate]

What is the more correct definition of angular momentum $\vec{\mathbf{M}}$ in three dimensions? (I.e. classically/Lagrangian/Hamiltonian, not necessarily quantum or relativistic) ...
1answer
182 views

### The strength and control over the strength of electromagnets, correlation between the strength and weight of the magnets

I am currently working on a project that aims to use the attraction & repulsion between two electromagnets as an alternative to weights, from a physiotherapy and rehabilitation perspective to help ...
1answer
29 views

### A Formula for the Phase Difference Between the Electric and Magnetic Wave Oscillations?

A) Is there a formula for the phase difference between the electric and magnetic field oscillations, in vacuum, in an electromagnetic wave emitted from an antenna, as a function of the frequency the ...
1answer
188 views

### Hidden momentum

I'm trying to learn about hidden momentum. After reading what I could find with a google search, I understand that it is equal to the momentum carried by radiation, calculated with the Poynting ...
0answers
19 views

### Does a cathode ray tube emits electromagnetic waves from a steady DC electron beam?

In cathode ray tube, heated cathode emits stream of electrons but when I wrap a coil around tube a current will be inducted in that coil? after all electron beam is a steady DC current? so no emf?
0answers
38 views

### Can someone explain me magnetic potential? [duplicate]

I don't understand why we can write the magnetic field as a potential vector A, and what exactly this potential is. Is it just a mathematical thing? And how can it help me calculate the magnetic ...
1answer
142 views

### Energy conservation of permanent magnets engine

How to explain the fact that magnet can attract an object (apply a work W) without losing a (significant) part of its internal energy? How to apply the energy conservation principle? Please think to ...
1answer
114 views

### Why is U(1) the gauge group in classical electromagnetism?

Can anyone give a physical reason that $U(1)$ is the gauge group for classical electromagnetism? I am familiar with the principal bundle formalism for Yang-Mills theory and see that since the Lie ...
2answers
908 views

### Do intergalactic magnetic fields imply an Open Universe?

According to a paper on the arXiv (now published in Phys Rev D), they do. How credible is this result? The abstract says: The detection of magnetic fields at high redshifts, and in empty ...
0answers
240 views

### Galactic binary engine found in the center of the Milky Way? [closed]

It is accepted science that Sagittarius A* is the black hole in the middle of our galaxy, and motion measurements of Sag A* show that it is more or less stationary relative to our Sun, so why would ...
2answers
22 views

### Should static electricity affect a Crookes radiometer?

I've been playing around with a Crookes radiometer for fun and I happened across something I can't figure out. I know the fundamentals of the radiometer (e.g. partial vacuum, thermodynamics, etc.), ...
0answers
38 views

### Eigenstates of 2D harmonic oscillator in a constant magnetic field

I want to find the eigenstates of the 2D harmonic oscillator in a constant magnetic field $\vec B = \vec B(x,y)$. My Hamiltonian reads $H_0 = H_{xy} + H_z$ where $H_{xy}$, is the hamiltonian of the ...
0answers
31 views

### why was necessary the discovered of electromagnetism? [on hold]

Need to know much more for the necessity of electromagnetism. http://www.ck12.org/physical-science/Discovery-of-Electromagnetism-in-Physical-Science/lesson/Discovery-of-Electromagnetism-MS-PS/
1answer
207 views

### Can the physical properties of the EM field be described directly from the 4-gauge potential?

I'm trying to make an argument that classically, the EM field is considered a more 'real' physical quantity than the potentials, and am tempted to say that the fact that the field carries energy & ...
0answers
22 views

### A bar magnet is brought close to, but does not touch, a paper clip [on hold]

The paper clip moves toward the magnet. What does this observation show about the field associated with the bar magnet?
1answer
96 views

### What is relationship between electromagnetic mass and rest mass?

Is there a direct equation which compares rest mass $m_°$ and electromagnetic mass $m_{em}$? Nothing on web I found. $m_{em} = \frac{4 E_{em}}{3c^2}$ 4/3 problem The final solution of the ...
1answer
169 views

### Find magnetic field in a solenoid for different regions?

A steady current I flows along an infinitely long hollow cylindrical conductor of radius R. This cylinder is placed coaxially inside an infinite solenoid of radius 2R. The solenoid has n turns per ...
0answers
31 views

1answer
28 views

### What causes a charged particle to follow circular motion in a magnetic field? [duplicate]

I would like to know why particles follow a circular path in a magnetic field, what path they trace and how this path is measured and controlled?
2answers
336 views

### How does back-emf oppose the input-current?

A circuit, has current $A$ flowing at a certain $V$. When there is a change in magnetic-flux, based on Faraday's law of induction & Lenz's law, we know that there is change in Potential ...
1answer
50 views

### Relativistic transformation of electrical current [on hold]

If, in frame $S$, we have an electrically neutral wire with some current $I$, modelled as positive charges moving in $x$ direction and negative charges moving in $-x$ direction, then how would one ...