Elecrtomagnetism Definition and 143 Threads

Say we have a coil connected to a battery in a uniform magnetic field, perpendicular to the magnetic moment of the coil. This is a simple motor. There is a torque on the coil that varies with the angle θ between the field and the moment. Clearly, the angular velocity ω is not constant. Here is...

I have recently studied about relativity being the reason for magnetism. The example given was about a magnetic field generated from current down a long wire. When two such wires with current in the same direction were parallel to each other there was an attractive force between them because...

I am reading Maxwell's "a treatise on electricity and magnetism, Volume 2, page 156" about "Ampere's Force Law". I have some confusion in the following pages: My question is of two parts: 1.Equation 20, i.e. ##P=\dfrac{B+C}{2r}## is the outcome of special case (i.e. l=1, m=0, n=0) But in...

Hi, I'm taking an undergrad course in Electromagnetism and Optics, and in the lecture notes it reads: "Consider the formal equation ε0D⋅E = 1 ... that must be obeyed for waves traveling in different directions as defined by the wave vector k but with a given energy density." Could anyone help me...

I know formula ## p=\frac{h}{λ} ## p is photon momentum h is plankc constant λ is EM-wave wavelenght but it is only valid for one wave. How to describe most general EM- field in terms of photons? Is there always discrete number of photons? If EM field is given in terms of a)EM-vectorfield...

I want to know the angle of view from which Lenz's law and Faraday's law can be seen methodically.

Homework Statement A particle with charge ##e## and position vector ##\vec{r}## (relative to some frame, S) moves with constant velocity ##\vec{v}##. A second charge ##e'## is moving with the same velocity ##\vec{v}## through the field generated by ##e##. If ##\vec{d}## is a vector from ##e##...

Homework Statement 1. Homework Statement [/B] Prove the potential energy of interaction between an electric charge ##q## moving with velocity ##\vec{v}## and an electromagnetic field with potentials ##V## and ##\vec{A}## is given by ##U = qV-q \vec{v} \cdot \vec{A}## Homework Equations...

Homework Statement [/B] In a thin rectangular metallic strip a constant current I flows along the positive x-direction, as shown in the figure. The length, width and thickness of the strip are l,w and d, respectively. A uniform magnetic field B is applied on the strip along the positive...

I'm not sure if the title correctly says what I am looking for. I'm a few years out of college and I'm trying to review some electromagnetics topics. A lot of the "proofs" in my EM book seem to take a lot of shortcuts, or use "intuition" to explain why some calculus operation can be simplified...

Homework Statement This problem propped in my head yesterday related to a project I'm working on (not homework, I'm not in school, but I thought this was the best place for it) and I just can't figure out how to crack it! If we have a large plate made up of nxn smaller plates, what is the...

Homework Statement [/B] I have two spherical metallic shells with radius ##3a## and ##a##, the little one is placed inside the larger so that the center of the little one is at a distance of ##a## from the center of the larger. The outer one has a charge ##3Q## and the one inside has a charge...

Homework Statement We know that coulomb's law describes the force between two charged bodies as proportional to the magnitudes of the charges and inversely proportional to the square of the distance. Of course, like charges repel and unlike attract. Now theoretically, if we placed two...

Homework Statement Greetings. Can someone give me hint how to solve following problem: Homework Equations From my understanding, you need following formula to solve problem: and then potential can be obtained by integrating over the current distribution. But right now these foormuas really...

I don't know why I was persuaded that in the free space, the electric field of an EM wave is always orthogonal to the direction of propagation. I've recently read my old textbook, and found that this is true only when the wave is far from the emitting source. But if I've understood right the...

Homework Statement a) A charge q is released a distance d above a grounded infinite conducting plane. It's non relativistic velocity is v. Find the induced surface current density on the plane. b) Show that the above current density produces a vanishing magnetic force on the charge. Homework...

Divergence theorem states that $\int \int\vec{E}\cdot\vec{ds}=\int\int\int div(\vec{E})dV$ And Gauss law states that $\int \int\vec{E}\cdot\vec{ds}=\int\int\int \rho(x,y,z)dV$ If $\vec{E}$ to be electric field vector then i could say that $div(\vec{E})=\rho(x,y,z)$ However i can't see any...

Will copper behave as a dielectric in high frequencies?...I tried to answer the question with loss tangent but relative permittivity of copper posed a problem...everyone on internet opines differently about relative permittivity of metals...then I looked at skin depth which decreases with...

Hello, I am trying to find out if there are any differences between how the Electric engine for car works vs how an Electric Engine for Drone works. I am sure the both consist of an Ignition coil, stator and rotor. However I have not been able to find the any schematics for a drones electric...

I have read that reactive power sustains/ supports voltage. What is the reason behind this?

Homework Statement Three equal charges with charge q and mass m are placed into an equilateral triangle of side length L. Find the speed of each when they are infinitely far from one another. Homework Equations -ΔU =ΔK (since the electric force is conservative), U= 1/4πε Σq1q2 /r The...

Homework Statement This is problem 3.4 from Prucell and Morin if you have the book. Homework Equations None The Attempt at a Solution Electric field inside a conducting sphere is zero. Let P be a point on one of its equatorial plane. The field along the plane is zero. So I know the charge...

Hi people, I studying electromagnetic waves (intermediate) and I don't understand how the expression for linear momentum of a wave is obtained, if the wave doesn't carry any mass. In particular, I have to explain why the radiation pressure on a perfect absorber is half that on a perfect...

Homework Statement A dipole of moment ##\vec{p}## where p is fixed, moves with velocity ##\vec{v}## though a magnetic field ##\vec{B}##. Show that the force on the dipole is ##\vec{v}\times(\vec{p}\cdot\vec{\nabla})\vec{B}+\dot{\vec{p}}\times\vec{B}##. Homework Equations...

I have a doubt about Ampère's that keeps me awake at night haha, but I think that for a more knowledgeable person it may seem pretty obvious. I've seen in several books that, in a coaxial cable with equal and opposed currents in the core and shield, the magnetic field outside the outer conductor...

A 5μF capacitor is connected in parallel with a 2MΩ resistor and the combination is then connected in series with a 1MΩ resistor through a switch to a 12V battery. Find the time taken for the voltage across the capacitor to rise from zero initial value to 2V after the switch is closed.From what...

I was studying for (first year) physics class and was playing around with the Bohr Model of Hydrogen. I tried calculating the electric potential at the Bohr radius r =5.29e-11 m, where V = \frac{e}{4 \pi \epsilon_0 r} (from the point-charge formula for electric potential) and I got 27.19 J/C...

The title is explanatory. I know that an iron core yields a stronger electromagnet. What if you have an electromagnet with an extremely tiny air coil relative to its volume? Does the small air coil diameter effect the electromagnet?

Homework Statement A charge (q) is placed in-between two other equal charges named Q. Q-----q-----Q a) If both Q's are positive, is charge q in equilibrium? If yes, is it a stable or unstable equilibrium? b) What about if one Q is negative while the other is...

Im trying to compare, visually in my head, the difference between transmitting data vs something like radio or microwaves vs how inductance and capacitance. I understand that the way the wave is modulated for example, AM or FM, can be interpreted as 0s or 1s. Im trying to compare this to...

Hey there - just a simple question. I've heard of the electroweak and grand unification energies, but was wondering if there was such thing as an electromagnetic unification energy. If such a thing exists, do we know what that energy is?

There is a frame that circles around a point because of the Lorentz force. Frame is placed between North and South magnets and there is s current flowing in a frame. My question is - can a charge in a wire move in a circle - for instance clockwise? I mean, if the square frame turns, then the...

Homework Statement A sphere with radius R has a spherically symmetric charge density that varies as 1/r. What is the electric field outside and inside the sphere? Homework Equations E=kQ/r^2, ε=permitivity of free space, Q=total charge, ρ=charge density, dτ=infinitesimal volume The Attempt at...

Homework Statement I need to show that $$\del*\vec{A(\vec{r})}=\frac{\mu}{4\pi}\int{\frac{\vec{J{vec\r'}}}{\vec{R}}}d\tau=0$$ where A is the vector potential and R refers to "script r" or (r-r') where r is source point of charge and r' is the measurement point. tau refers to a volume integral...

My question stems from a discussion I had with my colleague today. In Electomagnetic coupling , like in waveguide structures. We apply pertubation theory to find out the coupling between various modes that get coupled in the device. My colleague said that the coupling interaction was...

Can someone walk me through calculating the final step in this problem. Problem statement: If the charge q is produced by adding electrons to the mass, by how much will the mass be changed? It was calculated that the charge q is 2.374 * 10^-7 C which is correct and I know that we need to...

Homework Statement a small spherical insulator of mass 6.00×10−2 kg and charge +0.400 μC is hung by a thin wire of negligible mass. A charge of −0.220 μC is held 0.290 m away from the sphere and directly to the right of it, so the wire makes an angle theta with the vertical. What is the angle θ...

Hi 1)Is this sentence right? When we say for example the wavelength of red light in vacuum is 750 nm it means that the length of electric field and magnetic field that are perpendicular in the propagation direction of wave is 750 nm in one cycle? 2) We say that oscillating charges in antenna...

Problem statement: The E field measured just above a glass plate is equal to 2 V/m in magnitude and is direct at 45° away from the boundary, as shown in the figure. The magnitude of the E field measured just below the boundary is equal to 3 V/m. Find the angle theta for the field in the glass...

In an inductor, a current waveform 90o out of phase with the voltage waveform creates a condition where power is alternately absorbed and returned to the circuit by the inductor. If the inductor is perfect (no wire resistance, no magnetic core losses, etc.), it will dissipate zero power. I...

Homework Statement Turns of wire would around a toroidal core, carrying a sinusoidal alternating current i(t), represent a toroidal coil in my case. My question is, does magnetic force affect a non-moving charge outside of toroidal core and is there a magnetic field outside of toroidal core...

Homework Statement This is Problem 7.6 from Electronic Properties of Engineering Materials by Livingston. "Over a wide range of frequencies, the dielectric constant of a polymer is found to be proportional to the inverse square root of frequency. (a) How does the phase velocity of EM-waves...

Apologies for the melodramatic title. In studying AC current distribution in cables (skin effect), one can view the AC current as producing a time varying magnetic field in phase with the current itself (Ampere's Law). This in turn creates an electromotive force 90 out of phase with the current...