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2
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2answers
79 views
+50

Relating Poyntings theorem to Lenz and Faraday's law?

In system's similar to a motor, where the armature begins to accelerate simultaneously there is induced $-\epsilon$ to reduce the applied current(hence the applied power $P(t)$ is also reduced), or ...
0
votes
0answers
5 views

How do you calculate the charge on a conical pendulum with capacitance in a magnetic field?

A conducting wire of length L supporting a metal sphere of mass m and capacitance C is hung from a grounded rigid pivot and made to rotate as a conical pendulum at angular frequency ω. A uniform ...
0
votes
0answers
27 views

Does an electromagnet use more energy when it is repelling another magnet?

Kind of a strange question. Is the amount of energy used to power an electromagnet directly proportional to the amount of work an electromagnet does? That is, if I were to power an electromagnet ...
4
votes
1answer
3k views

Force on Earth due to Sun's radiation pressure

I have been asked by my Classical Electrodynamics professor to calculate the force that the Sun exerts in the Earth's surface due to its radiation pressure supposing that all radiation is absorbed and ...
2
votes
2answers
153 views

Momentum around an accelerated electron

Assume that an electron is accelerated along the +x-axis. The electron will radiate electromagnetic energy and momentum in every direction. But it seems to me that the EM momentum it radiates in ...
0
votes
1answer
122 views

potential inside a cylindrical shell in terms of the surface potential?

Given a potential distribution $V(\phi)$ at the surface of an infinite cylindrical shell, is there an easy way to derive the potential inside the cylinder. No charges or currents anywhere.
1
vote
1answer
376 views

Induced electric field due to a moving wire

An infinite wire carrying a constant current $I$ in the $\hat{z}$ direction is moving in the $$y$$ direction at a constant speed $v$. Find the electric field, in the quasistatic approximation, at the ...
1
vote
0answers
23 views

One from Landau's Minimum (Macroscopic Electrodynamics)

A dielectric sphere with the electric and magnetic susceptibilities ε1 and µ1 is rotating with angular frequency ω in a constant electric field E~ in a medium, characterized by the parameters ε2 and ...
0
votes
0answers
14 views

Electric field produced by polarized medium at the surface of a conductor

Suppose we have some conducting sphere of radius $R$ and charge $Q$ submerged half way into a medium with permittivity $\epsilon_1$. I have deduced that the electric field produced by the sphere will ...
3
votes
1answer
65 views

Introductory literature on the multipole expansions including toroidal moments

I wish to understand the general idea of the multipole expansion in the context of classical electrodynamics and, especially, the concept of the toroidal moments. All the papers on the subject I've ...
0
votes
1answer
19 views

How do I show for an ideal transformer $M^2=L_1L_2$?

I've been stuck on this problem for about an hour. In an ideal transformer, the same flux passes through all turns of the primary and of the secondary . Show that in this case $M^2=L_1L_2$, where ...
4
votes
2answers
167 views

Far field diffraction of EM waves: what does the zero frequency signify?

If you have a system of independently radiating electrons/point-charges, the far field distribution of the EM waves can be approximated by the Fraunhoffer diffraction integral, or simply by the ...
4
votes
2answers
37 views

Stored energy and momentum in a magnetic field?

How is it possible for a magnetic field to store energy and momentum? And can deliver it to another object(charge/dipole) or field? I can't depict it. I know it occurs but how? For example, the ...
0
votes
1answer
44 views

Motion of Particle due to Lorentz Force

So my professor gave us the following question: A particle with electric charge $Q$ and mass $M$ is initially traveling with velocity $v_0$ in the $x$ direction at time $t= 0$. There is a constant ...
0
votes
1answer
352 views

What are the boundary conditions for EM waves normally incident on the interface between two dielectric media?

An EM wave, amplitude $E_0$, frequency $\omega_0$, is incident upon a material with relative permittivity (dielectric function) $$\varepsilon \left( z \right) = \left\{ \begin{gathered}{\varepsilon ...
4
votes
2answers
212 views

What is the area in Faraday's law if we have only a piece of metal moving in a magnetic field?

If a piece of metal of length $l$ is moving with a speed $v$ in a region where there is a uniform magnetic field $B$ perpendicular to it, there will be a potential difference across its terminals ...
0
votes
1answer
40 views

Why does the energy of the mechanical wave depend on frequency but the EM wave does not?

Why does the energy of the mechanical wave depend on frequency but the EM wave does not? Are there any implications?
3
votes
1answer
60 views

Is this a valid Gauge fixing condition?

I've been given the following gauge fixing condition: $$A_\mu A^\mu = 0 $$ And I've been asked to show if it is a valid gauge fixing condition or not. I believe that it isn't because I've already ...
0
votes
5answers
231 views

Applying Newton's 3rd law in electromagnetic systems

From this diagram: What is the action force here, and what is the reaction force? From two references, the wire and the magnet? *Assume the magnet being an electromagnet(air core, basically a ...
3
votes
2answers
95 views

Does light interact with electric fields?

We know that light is an electromagnetic wave and it does interact with charges. It contains magnetic field and electric field oscillating perpendicularly but when we apply an electric or magnetic ...
0
votes
2answers
52 views

Negatively charged ball orbiting positively charged ball in space?

Would it be possible to make something like two metal balls, one positively charged and one negatively charged, in space, where the negatively charged ball would orbit the positively charged one like ...
1
vote
0answers
13 views

Force on a magnetic dipole due to a magnetic field

Imagine a solenoid which has current $i$ and is producing a magnetic field $B$ which equals $$B=\mu N i$$ Now, imagine we put a small cylindrical magnet at the end of the solenoid. Then because at ...
2
votes
1answer
61 views

Penning Trap Simulation

I'm currently working on a particle tracker and I would like to implement a Penning trap. I think I might have a problem with the field of the electrical quadrupole. My idea was to place 2 dipoles and ...
1
vote
1answer
313 views

The image current due to moving charges and a current carrying thin wire

Suppose we have a plane conductor and positive charged particles of mass m are moving parallel to the plane conductor at a distance d. The trajectory can be assumed to be straight. An image current ...
1
vote
0answers
33 views

induced current in loop

I'm re-asking this question that was posted by @zhzh and subsequently closed. If you have a loop that is spun clockwise as a magnet is moved near it, is a current induced in that loop? If the ...
4
votes
14answers
2k views

Metallic and glass sphere of same size released at a height

This question was in my exam today : A metallic and glass sphere of same size were dropped at same height. Which sphere would hit the ground first and why? I have thought about several things and ...
0
votes
2answers
45 views

A static electron and a radiating electron

Let us consider an electron A, which is at rest in one frame of reference and another electron B which is accelerating in that frame of reference. Now the fields due to electron B are time varying . ...
4
votes
1answer
88 views

Why are agglomerated gold nanoparticles black?

I put a drop of aqueous red colloidal gold on a glass. After the drop dried I saw that remaining nanoparticles were black instead of red. Why black? Does it mean that plasmon resonance is so strong ...
1
vote
0answers
28 views

What does the density of points (tail point of the vectors) represent in the geometrical representation of a vector field? [closed]

While trying to understand the divergence of a vector through the geometrical representation of the vector field, I found that pictures can be misleading. Even a vectors field which looks to be ...
0
votes
2answers
213 views

Drift Speed and Current in Two Different Inertial Frames

We have a long, cylindrical wire carrying a constant current I in an inertial frame. At a distance of R from the center of the wire, the magnitude of magnetic field is $μI/2πR$. What is the magnitude ...
2
votes
0answers
61 views

Classical electrodynamics as an $\mathrm{U}(1)$ gauge theory

Preface: I haven't studied QED or any other QFT formally, only by occasionally flipping through books, and having a working knowledge of the mathematics of gauge theories (principal bundles, etc.). ...
1
vote
1answer
43 views

How to understand the continuity equation $i\omega \rho=\nabla\cdot\mathbf{J}$?

Suppose that $\mathbf{J}$ is alternating current and its intrinsic frequency is $\omega$, i.e. $\mathbf{J}(\mathbf{r}',t)=\mathbf{J}(\mathbf{r}')e^{-i\omega t}$ , and $\rho$ is charge density. Then my ...
0
votes
1answer
21 views

Conservation of momentum in electrodynamics and force on the northern hemisphere of a uniformly charged sphere

In chapter eight of his book "Introduction to Electrodynamics", Griffiths gives the following example: "Calculate the net force on the 'northern' hemisphere of a uniformly charged solid sphere of ...
11
votes
4answers
439 views

Is the electromagnetic mass real?

In his Lectures on Physics vol II Ch.28-2 Feynman calculates the field momentum of a moving charged sphere with charge $q$, radius $a$ and velocity $\mathbf{v}$. He finds that the total momentum in ...
15
votes
4answers
651 views

The problem of self-force on point charges

Allow me to preface this by stating that I am a high school student interested in physics and self-studying using a variety of resources, both on- and off-line, primarily GSU's HyperPhysics website, ...
1
vote
1answer
223 views

Magnetic dipole and magnetic moment

I don't quite understand the meaning of these terms. My physics book just gives the mathematical definition of magnetic moment as $\mu=Ia$, which means nothing to me. I know it has to do with torque. ...
11
votes
9answers
10k views
0
votes
0answers
22 views

magnetostatics and time varying fields

Mathematical statement for magnetostatics is $\nabla\cdot \mathbf{J}=0$ which accounts for no piling of charge and hence no time varying field term in the 4th Maxwell's equation.Are there any possible ...
4
votes
0answers
90 views

Why is there no induced current in this loop? [closed]

This problem comes from Barron's SAT Subject Test Physics book. A loop of wire and a bar magnet are moving relative to one another. Which motion in the diagrams shown below will NOT induce a ...
2
votes
1answer
168 views

Method of image charge for cylindrical conductor

I am simply puzzled that only for spherical and planar conducting surfaces the method of images is applied. Is it (really) impossible to find image charge or charge distribution which can simulate the ...
0
votes
1answer
40 views

emf of a moving wire in a variable magnetic field

Lets, say that Magnetic filed is either (case 1) $B=B_0$ or (case 2) $B=B_0\sin{\frac{\pi x}{L}}$in $z$ direction. We have a wire with a length of $L$ along $y$ axis which is moving in $x$ direction ...
3
votes
2answers
542 views

Frequency of rotating coil

Given a coil initially in the x-y plane, rotating at angular frequency $ \omega $ about the x-axis in a magnetic field in the z-direction. This uniform time varying magnetic field is given by $B_z ...
3
votes
1answer
74 views

Are the conducting electrons in a metal counted as free or bound charges?

Caused by another question on the propagation of EM waves in a metal, I got a bit confused on the notion of free and bound charges in a metal (sometimes called induced or external). Are the free ...
1
vote
0answers
27 views

Capacitor connected across two isolated sources [duplicate]

Lets say there are two isolated sources of positive charges $q_1$ and $q_2$ $(q_1>q_2)$ located sufficiently far apart. If the two are connected to the two plates of a capacitor, then what is the ...
1
vote
0answers
23 views

Find electric field induced by magnetic field using maxwell equations [closed]

I am a newbie to Maxwell Equations so I'd appreciate some tip. Consider a uniform time-varying magnetic field $$\vec B_{0}(t) \hat{z}.$$ The problem is to find induced electric field using ...
0
votes
2answers
43 views

Torque on a disk with charge

Imagine you have a disk with some number of charged metallic spheres spaced equally around a disk at some distance from the center of the disk and those spheres are mechanically attached to the disk. ...
7
votes
1answer
232 views

Motion in a time-dependent uniform magnetic field

Suppose you have an infinite solenoid generating an uniform magnetic field inside. The field is oriented along the solenoid axis : unit vector $\vec{\bf n}$. The field intensity varies linearly with ...
0
votes
1answer
27 views

Induced EMF, by moving the magnet is the same?

I know that when a wire is moving in a magnetic field, there is an induced EMF due to the change in area, therefore, a change in magnetic flux. However, what if things we're switched? Fixing the ...
1
vote
2answers
85 views

How does a charge distribution evolve with time? (in classical electrodynamics)

It is often stated that, in classical electrodynamics, the electric and magnetic fields determine uni vocally the dynamics of a charge distribution distribution (how it evolves in time). I can more or ...
12
votes
4answers
404 views

How does the emf “know” what the magnetic flux is?

I came across an example in my book where it has the changing flux from a solenoid passing through a larger ring at the end. Here's a picture: How does the large loop (or radius $r_1$) even ...