Electromagnetism Definition and 830 Threads

I need help in calculating the magnetic field outside of an iron core solenoid at different distances. I have made an electromagnet by taking a 99.99% pure iron (5cm in length and 1 mm in radius) and wrapping wire over it. I have measured it's magnetic field at the end and cannot find an...

hi, I would like to put into words that I really wonder how these lagrangian or lagrangian densities are created. For instance in the link at 59.35 suskind says $$\int A^u dx^u$$ is invariant or action integral. How is this possible ?Could you provide me with the proof?

Homework Statement We want to calculate the field of a uniformly polarized sphere of radius=R Homework Equations V(\vec{r}) = \frac{1}{4 \pi\epsilon_{0}} \oint_{S} \frac{\sigma_{b}}{r} da' + \int_{V} \frac{\rho_{b}}{r} d\tau' The Attempt at a Solution i)I know that \sigma_{b} = P...

So here is my question, and maybe I am not asking it right, but here we go: If electromagnetism prevents me from actually touching anything at a quantum level, how is it that I can get cut by a knife, or get a road rash falling off my bike? If the negative field of electrons that surround...

I was trying to understand how the electric & magnetic forces are related. I was going through the equations & the simple explanation of relativistic magnetic field given everywhere. Which goes like this... There is a current carrying conductor & a charge capable of moving outside it. The...

I've been recently trying to understand the concept of paramagnetism, but I feel like I'm running into 2 conflicting models. Stern–Gerlach seems to suggest that electron spins always point up or down to an incident magnetic field, regardless of their spatial orientation. Similarly, when...

Hi guys, I'm just curious about how does Classical Electrodynamics by Hans Ohanian and Electromagnetic Fields by Ronald Wangsness compare? I know Griffiths is like the way to go when it comes to EM, but personally, I find his book too hand wavy and the explanations are sometimes lacking, so I...

Can anyone please help I want to calculate the power required to make a electromagnet of strength 1 tesla and length 600km. And how much energy a train consume in traveling per km with speed of 112km/h

Hi Everyone, I'm trying to justify to myself why |F(a)| > |F(b)| > |F(c)| I think I can see why |F(b)| > |F(c)| due to special relativity case c observed from the charges point of view would observe the charges closer due to lorentz contraction. As the charge is invariant would result in...

In special relativity, the electromagnetic field is represented by the tensor $$F^{\mu\nu} = \begin{pmatrix}0 & -E_{x} & -E_{y} & -E_{z}\\ E_{x} & 0 & -B_{z} & B_{y}\\ E_{y} & B_{z} & 0 & -B_{x}\\ E_{z} & -B_{y} & B_{x} & 0 \end{pmatrix}$$ which is an anti-symmetric matrix. Recalling the...

Homework Statement The volume between two infinite plates located at x=L and x=-L respectively is filled with a uniform charge density ##\rho##. Calculate the electric field in the regions above, between and below the plates. Calculate the potential difference between the points x=-L and x=L...

Homework Statement Can someone explain what regenerative breaking is? Homework Equations no equations required The Attempt at a Solution I understand that this occurs with electric cars. It uses the idea that the electric motor and the electric generator are so similar. But how does the...

Homework Statement Homework Equations no equations are required The Attempt at a Solution is this correct? [/B]

I originally posted this to the advanced homework -section, but maybe this isn't advanced enough to warrant being posted there :oops:. If a mod sees this, feel free to delete the original on the other forum. I'd do it myself, but I can't. 1. Homework Statement Calculate the mutual inductance for...

I have noticed there are a few designs for permanent magnet brushed DC motor, but I can't seem to find the benefits and downsides of either one. The first one (first attachment) uses three electromagnets placed on a triangular rotor. There are two arc permanent magnets on the outside. In this...

I have been reading up on electric bike motors, there are a few things regarding size and wire gauge that have me confused. I have seen disassembly videos of around 300 watt electric bike motors with planetary gears, and I can't see how anyone can push through 300 watts through the wires without...

How large would a superconducting magnetic energy storage device be if it were to safely carry 100 kilowatt-hours of energy? How much cryogen (liquid nitrogen) would it consume per hour if the device were made from high-temperature superconducting materials (YBCO or similar).

Homework Statement Homework Equations ##\oint_{C} Bd\ell = \mu I_{enc}, B_{normal}## continuous across boundary, ##H_{parallel}## continuous across boundary The Attempt at a Solution $$\oint_{C} Bd\ell = \mu I_{enc} \rightarrow B = \frac{\mu NI}{2\pi r}$$ Any help much appreciated. How...

Laplacian for polars: $$\frac{1}{r}\frac{\partial}{\partial r}\left( r\frac{\partial \phi}{\partial r}\right) + \frac{1}{r^{2}}\frac{\partial^{2} \phi}{\partial \theta^{2}} = 0$$ This is in relation to a problem relating to a potential determined by the presence of a wedge shaped metallic...

Hi- Sorry if this is a silly question, but by definition the magnetic flux is given by integral B dot dA. But From Gauss' law for magnetostatics is this not zero around a closed loop? So would that not then imply that the EMF around any closed loop is zero? Obviously I'm missing something, so I...

Is it me, or the overall problem in CED is not addressed anywhere? Statement of the problem: Let there be two massive electrically charged particles of invariant masses m1 and m2 and electric charges q1 and q2, respectively. They are free to move arbitrarily in Minkowski spacetime endowed with...

When a particle (or any objects) accelerates when acted upon by fundamental forces, what is happening to the amount of energy in that particle? A large example would be an asteroid in space caught by Earth's gravity and accelerates toward Earth as a result. The fundamental forces here can be...

Homework Statement Two identical parallel-plate capacitors, each with capacitance 10.0 μF, are charged to potential difference 50.0 V and then disconnected from the battery. They are then connected to each other in parallel with plates of like sign connected. Finally, the plate separation in...

We assume that there is no electric field inside the perfect conductor because relaxation time of metal is very short. whereas J=sigma*E But if this is the case, how can current flow inside the metal? -Is this because of battery? If there is a battery connected to a metal...

Hello! In this thread, in this answer, my statement "A time-varying electric field creates a magnetic field which is time-varying itself" was refuted. Because I never observed this before, I would like to discuss about it. As far as I know, Maxwell's equations are valid always together, that...

Homework Statement What will be the final velocity of a proton (when it is very far away) if it it released from rest at the center of a uniformly charged hoop and given a slight push in one direction. assume it follows the axis of the hoop. mass of proton: m = 1.67x10-27 kg charge of proton: q...

We know that EMW are generated by accelerating charges. If I accelerate a charge it should gain kinetic energy equal to half the mass of the charge times velocity squared. But at the same time it will radiate electromagnetic waves which carry energy itself. So where does this energy come from...

Hello everyone, Lately, I have been reading and studying the Maxwell's https://es.wikipedia.org/w/index.php?title=A_Treatise_on_Electricity_and_Magnetism&action=edit&redlink=1 https://es.wikipedia.org/w/index.php?title=A_Treatise_on_Electricity_and_Magnetism&action=edit&redlink=1 Thanks for...

Homework Statement Three electrons form an equilateral triangle 0.800 nm on each side. A proton is at the center of the triangle. Homework Equations U = k[(q_1*q_2)/r] The Attempt at a Solution I tried to use the following equation: k*[(3e^2)/(0.8*10^-9) - (3e^2)/(0.4*10^-9)] I plugged in...

Hello! I still would like to thank those who participated to my previous thread about group velocity and dispersion. Now there is a (maybe) simpler question. A sinusoidal, electro-magnetic plane wave in the vacuum propagates in a certain direction with the following wavenumber, which is supposed...

Hello! In this previous post, most replies point out that it is not possible to predict the angle of refraction (and so the frequency) at a certain interface, given the wavelength of the original signal. In particular, But when dealing with optical waveguides, it seems to be different. I am...

I have trouble understanding how a receiver doesn't get bombarded with frequencies... and exactly how does a receiver only "accept" certain frequencies? I understand if you send energy(or electricity) through a copper wire (and other types of metals) it makes a frequency with certain hertz...

I was researching about the discovery of electromagnetism and how Johann Ritter (Discoverer of ultraviolet light) used silver chloride to discover the heat of ultraviolet light but why couldn't Sir william Herschel discover it with just a thermometer like infrared light?

I was told in high school that Rutherford's atomic model was wrong because an electron which is in acceleration must release energy. That's how electromagnetic waves are made. and then I was told that Bohr gave his model and solved this problem. By making energy quantized. But what I really...

Homework Statement Suppose light of momentum -P\hat{\textbf{k}} is shone on a sphere of radius R. What is the momentum transferred onto the sphere? Homework Equations The Attempt at a Solution I think the transferred momentum upon reflection is given by (-2P\hat{\textbf{k}} \cdot...

Is there a formalism that relates the properties of energy (electromagnetism) to the properties of spacetime (relativity)?

Hello! In this document a solution of Maxwell's equations in cylindrical coordinates is provided, in order to determine the electric and magnetic fields inside an optic fiber with a step-index variation. The interface between core and cladding is the cylindrical surface r = a. For example, the...

I'm supposed to find the magnetic field, the scalar electric potential and magnetic vector potential for the following electromagnetic wave: \vec{E} = E_0 cos (kz - \omega t) \left \{ \hat{x} + \hat{y} \right \} Alright, the magnetic field goes as \vec{B} = \frac{1}{c} \hat{k} \times \vec{E}...

Hello all I need help, please recommend a good source for electromagnetism for a high school student, but it should be a bit brief and gives a good understanding of the topic. I am supposed to go over merely those concepts in a matter of hours. - Inductor - Lenz's Law - Back emf - Inductor...

Homework Statement 1.0 mA proton beam accelerated through potential difference of 1 keV. Determine the volume charge density of the beam after acceleration assuming uniform current distribution within diameter of 5mm, with zero current outside of this. Particle starting from rest. Final answer...

Hello I hope you know the phenomenon called "Magnetic train". My teacher used it in classes to demontrate electromagnetic phenomena. So he told the advanced learners (however, here I am xD) to investigate it, especially the forces and how certain parameters affect the velocity. But I do not...

Homework Statement A coil, made up of 1850 loops, is inserted in an electric circuit and has a resistance of 45,0Ω. The area of each loop is 4,70⋅10^(-4) m^(2). The coil moves from a region where there's no magnetic field, to a region where the magnetic field is present. The normal to the coil...

Do electrons excite the EM field or do they just create virtual photons that do? If you could only see EMF excitations, would you see the electrons or virtual photons coming from the electrons?

In a source-free, isotropic, linear medium, Maxwell's equations can be rewritten as follows: \nabla \cdot \mathbf{E} = 0 \nabla \cdot \mathbf{H} = 0 \nabla \times \mathbf{E} = -j \omega \mu \mathbf{H} \nabla \times \mathbf{E} = j \omega \epsilon \mathbf{E} If we are looking for a wave...

Homework Statement A circular loop of radius R is on the xy plane and the center is at the origin, the current is flowing in a counter-clockwise manner. a) Let Q=(a,0,a) be a point such that a>>R. Find Br and Bθ at Q. b) Let Q=(ha,0,0) be a point on the x-axis such that h<1. Find the vector...

Hey, guys! I had a brief electromag question. If capacitance is defined as the amount of charge that can be stored in a capacitor per unit of potential difference, then technically can capacitors made from insulators still have a capacitance? The problem I'm considering is calculating the...

Hello. Is it possible that gravity is actually electromagnetism?

If a compass is placed above a current carrying wire, why does the compass needle align itself in the direction of the magnetic field produced by the wire?

I've always been taught: North poles attract south poles. Yesterday after studying electromagnetism, I've a question to ask. Here's a diagram: In circuits like these, this is how the north and south poles of these electromagnets are defined. Now my question is, is the reason that the South pole...

Is there an equation for elctromagnetism which describes it in terms of gravity; and vice versa? Thank you for your time and help and please correct me if I'm being ignorant!