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.

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3
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2answers
47 views

Introducing a phase, what changes?

This question is related to: Mach-Zehnder interferometer and the Fresnel-Arago laws Let us say we have unpolarised wave taking the form: $$\psi=\psi_0 e^{i(kx-\omega t)+i\phi(t)}$$ Where $\phi$ ...
0
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0answers
17 views

Electromagnetic Wave Impedance

In a derivation of the transmission and reflection coefficients for light incident at an angle onto a surface where we have a change in refractive indices the proof says that ...
1
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2answers
47 views

How does always the magnetic field lag the elctric field in a conductor?

In conductor, the relation between the phase of the magnetic field $\delta_B$ and that of the electric field $\delta_E$ is given by $$\delta_B-\delta_E=\tan^{-1}(\frac{\beta}{\alpha})$$ where $\alpha$ ...
0
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0answers
17 views

Free charges inside a conductor and propagation of EM wave

In Griffith's book on Electrodynamics, while discussing the propagation of electromagnetic wave in a conducting medium, he set $\rho_{free}=0$. He argues that, any extra charge given to the conductor ...
0
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1answer
30 views

Eddy currents in a superconductor

Just had a lesson we just had our teacher introduced the concept of eddy currents, and showed us how a magnet moves slowly through a metal tube due to the opposite generated magnetic field. If you ...
0
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1answer
27 views

Torque on a charged ring

I have been studying electromagnetic induction. As I understand, a magnetic field will exert a force on a moving charge. What I would like to know is whether a changing magnetic field will exert a ...
0
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1answer
24 views

Net magnetic field in a loop

The Ampere's law states that the net magnetic field in a loop is proportional only to the current inside the loop. So if we calculate the net magnetic field in figure 1 and figure 2 we would obtain ...
1
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2answers
62 views

Magnetism In Space

I am not an expert when it comes to physics. I was looking at maglev technology the other day and a thought crossed my mind. Would similar systems work for deep space exploration. I understand ...
0
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0answers
21 views

Magnetic Field from Portion of Infinitely Long Cylindrical Shell

I just had this question on an exam and got a weird answer. A $\theta=30^\circ$ portion of an infinitely long cylindrical shell carries current with density $J=\frac{di}{dl}$ in the $\hat{k}$ ...
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0answers
36 views

Photon transmission

I want to know exactly how light travels. Are each photon in a light beam traveling in a cosine function? I'm confused because only when it goes through polarization that it starts to show this type ...
1
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2answers
48 views

Why is the electric potential zero in this case?

The situation: a charge of $-2q$ is situated a distance $r$ to the left of a charge of $q$. What is the electric potential at a point $p$ a distance $r$ to the right of charge $q$? So basically: -2q ...
0
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0answers
28 views

Propagation Of Wave in Rectangular Waveguide

From what I understand, electric and magnetic fields are perpendicular to one another and the direction of wave propagation.The text book states that the direction of wave propagation in the ...
0
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0answers
19 views

Magnetic susceptibility anisotropy

I have some problems in understanding magnetic susceptibility anisotropy. I know that magnetic susceptibility can be described via a rank 2 symmetric tensor so the magnetization induced in a sample is ...
0
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0answers
26 views

Longitudinal Polarization and Spin-0 for Massive Vector Fields

I was wondering if anybody would be willing to explain how a plane wave solution of the form $\vec{B^\mu}=\epsilon^\mu{e^{k_0ct+\vec{k}.\vec{x}}}$ for a massive vector field's equations, say for ...
2
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0answers
61 views

Gauge transformations for Schrödinger equation [closed]

I want to prove the Schrödinger equation is invariant under the gauge transformations \begin{align*} \mathbf{A} & \rightarrow \mathbf{A}' + \mathbf{\nabla} \chi \\ \phi & \rightarrow \phi' - ...
0
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0answers
19 views

May the total charge in a supercapacitor be different using unipolar and bipolar voltage power supply?

Consider a supercapacitor where a Helmoltz double layer is formed at each of the 2 electrodes, which is like having 2 capacitors mounted in series, but with different polarities. The total charge at ...
1
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1answer
60 views

Induced current for conjoined loops in varying magnetic field

How do we calculate the emf and the current induced in two loops of wire, that have a portion in common between them? The specific example we had solved in class is: The left side loop is a square ...
1
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1answer
39 views

Probable mistake in the derivation of the vector form of Biot-Savart's Law

In the course of "Classical Electrodynamics", our professor stated Biot-Savart's Law as follows: $$\vec {dB}=\frac{\mu_0}{4\pi}\cdot \frac{i\vec {dl} \times \vec r}{r^3}$$ Then he proceeded to derive ...
-1
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0answers
28 views

Definition of a field as a condensate state of bosons

I would like to know if a single boson can create a field or is it a requirement to have a condensate state of them where the number of bosons is not determined. For example, if you create a single ...
0
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0answers
36 views

Electromagnetic field produced by a charge?

I guess vibration of a charge particle produces vibrating EM wave and oscillation of a charged particle will produce oscillating EM wave. If charge is only accelerating (speeding up) what will happen ...
1
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2answers
68 views

Which part of my idea is wrong about infinite energy produced by EMF for certain circumstance?

As a someone who is on the first year of EEE student, facts in a simple way: time varying magnetic fields around conductors produce electricity for outer space, object will keep going at the same ...
-1
votes
0answers
25 views

Torque of a current loop (circular) inside another one

I have a circular coil of 12cm of radius that conducts a current of $13A$. A second coil, with 50 turns, and a current of $1.3A$ is in the certer of the other one. I need to find: a) the magnetic ...
11
votes
4answers
514 views

Are EM radiation and EM waves the same thing?

Are EM radiation and EM waves the same thing? I have seen this topics treated separately in many books. It is still not clear to me whether EM radiation and EM waves are synonymous. Is there any ...
0
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2answers
31 views

Direction of magnetic field

How did we know that the direction of magnetic field is from north to south and not the opposite? For example, we may use iron filings, and they will take the shape of the magnetic field, but how we ...
0
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2answers
37 views

electrical field in coaxial cable

When getting the electric field between the outer and inner cylinder. why is it that we are only concerned with the field generated by the positive charge distribution on the inner surface and not ...
3
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1answer
69 views

Difference between radio waves and other electromagnetic waves?

Yes radio waves have different frequency and wavelength than others but it seems that radio waves are produced by sinusoidal current while other electromagnetic waves do not need need sinusoidal ...
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0answers
41 views

Frequency of Electromagnetic Radiations/Waves?

"A charge that is accelerated will produce variable electric and magnetic fields. These are electromagnetic waves. If the charge oscillates with a frequency f, then the resulting EM wave will have a ...
1
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1answer
32 views

Charge affected by EM-pulse. What is the equation of motion?

I'm studying for my test on radiation for Tuesday. I came across this exercise. Thought it looked interesting but now I'm stuck and I can't move forward before I finish this one. Exercise: A ...
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0answers
22 views

Two charged conducting spheres when placed in contact with each other [duplicate]

What happens when two charged conducting spheres of different radii are brought in contact with each other. How does it affect the charge distribution and field lines of spheres?
3
votes
0answers
39 views

What experiments confirmed Poynting's Theorem?

Actually, I have two related questions. The fist is the above question. The second is, what experiments confirmed that $\varepsilon_0\left(\frac{E^2}{2} + c^2 \frac{B^2}{2}\right)$ is the ...
0
votes
1answer
30 views

Why is the electric field homogenous inside a circuit?

In a circuit between to poles of a battery, there is an electric field accelerating the charges in the wire towards lower potencial (but due to resistivity they only travel at drift velocity). Is ...
0
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0answers
23 views

The radiation intensity considering dipole, quadrupole and magnetic dipole parts

In page 204 and page 205 of the book "The Classical Theory of Fields" written by Landau and Lifshitz, there is this sentence In averaging the square of the magnetic field, all the cross-products ...
0
votes
1answer
50 views

Magnetic force on a charged particle doesn't affect total energy

So there's this sentence in a book I am reading. It states "When a charged particle is placed within a magnetic field, despite the magnetic force acting on the particle, there will be no change in the ...
0
votes
1answer
40 views

Principle of capacitor

It is said that second conductor reduces the potential of fist conductor and hence increases charge taking ability of first conductor My confusion... As per my limited knowledge it is electric ...
0
votes
1answer
37 views

Biot–Savart law for a finite wire or the center of a square coil

I need to find the magnetic field inside the center square of a coil (I think this is the name, I'm translating, but if not, I'm talking about a loop of a wire, just 1 turn) of side $50cm$. So, I ...
0
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0answers
16 views

What is the energy density of a spinning orbiting ball of uniform mass with surface charge?

What is the energy density of a spinning orbiting ball of uniform mass with surface charge? I know that all the energies involved are mass-energy, spinning energy, orbiting energy, electric energy ...
-5
votes
1answer
74 views

What is exact difference between gravitational force and magnetic force? [closed]

I've read that gravitational force is due to mass only and magnetic field is due to moving charged particles. But my question is: what are other difference between them? Can we set up a small ...
0
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0answers
33 views

Electromagnetic Field caused by accelerating and oscillating charge particles?

Will accelerating and oscillating charges will cause EM waves of different shapes ? As EM waves are always shown as sinusoidal Electric and Magnetic Fields perpendicular to each other. Does it mean ...
-1
votes
3answers
37 views

Frequency of other light in white light [closed]

I have this question in mind because I read that the frequency of light depends only on the source of light. If we consider a source of white light then it emits light of different colours also. Then ...
1
vote
2answers
34 views

Finding the speed of electrons in a magnetic field

So I'm trying to solve this problem in which an electron beam is "drawing a picture" on a TV screen. The electrons are accelerated to a voltage of $3 kV$ by wire coils and are then directed to ...
0
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0answers
23 views

Charge Magnitude Based on Isoline Spacing

Suppose we have two positive charges of unknown magnitudes. We are given the isoline map (the equipotential lines) for the two-charge system. One has isolines more "squashed together" (more closely ...
1
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0answers
24 views

Wire with current in magnetic field $\vec{B}$has force $\vec{F_1}$. When rotated, $\vec{F_2}$. Find $B$ [closed]

I have the following question: In a wire with $10cm$ there is a current $4A$ going 'upwards' in the $z$ axis. The force over this field, under a constant magnetic field $\vec{B}$ is $F = -0.2\vec{i} ...
1
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1answer
49 views

Magnetic monopoles gauge theories

I'm quoting 't Hooft: "[...] Locally stable field configurations may exist that have some topological twist in them [...].Careful analysis of the existing Lie groups and the way they may be ...
2
votes
1answer
35 views

Is there any electric current in a continuous medium of moving charges?

Suppose that unlike in real life where charge is carried in fixed discrete chunks like electrons that one has a continuous fluid in a bottle that carries charges. Suppose that the fluid is stirred in ...
1
vote
1answer
89 views

Hamilton's equations of motion on Dirac's formalism

I'm having several doubts about the procedure proposed by the Dirac-Bergmann algorithm in order to get the correct equations of motion of electrodynamics (Maxwell's equations). Suppose I've already ...
1
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0answers
45 views

Electromagnetic waves and photons? [duplicate]

Electromagnetic waves are photons or photons cause electromagnetic waves ? Its said that when charges are accelerated we get electric and magnetic field that carries energy but then they say that this ...
1
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0answers
28 views

Why the motion of rotating magnet doesn't stop if we use a superconducting wire?

I would like to know why magnets rotated,wouldn't stop their motion if we place a superconducting wire as said by William Beaty at MadSci Network.
6
votes
3answers
198 views

How do electromagnetic waves carry energy?

Its said that electromagnetic waves carry energy. Is this because these waves are made up of electric and magnetic fields which can cause changes to the stuff that falls with in their range? Is that ...
3
votes
2answers
101 views

Can bending spacetime produce electromagnetic fields?

Let's say that we can somehow bent spacetime, can this produce electromagnetic fields? or EMF can only be emitted from charged particles of matter?
0
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2answers
67 views

Electromagnetic Radiation and Communication!

I read that the accelerated charges create electromagnetic field/spectrum which consists of following different waves: gamma, X-rays, ultraviolet, visible light, infrared, microwaves, & radio ...