Electromagnetism Definition and 829 Threads

I'm currently doing an experiment with magnetic levitation but I don't know if my independent variable will even affect my results at all. I am planning on building a rail of magnets and levitating a type 2 superconductor on it. I wanted to change the material surrounding the rail of magnets...

I don't really understand how to find the solution. I've tried to find the solution in books and google but still can't find it. In general, the Question 1 the problem is using the method of Image charge and Induced surface charge density. but this time my professor changed it to something else...

I need to use hermiticity and electromagnetic gauge invariance to determine the constraints on the constants. Through hermiticity, i found that the coefficients need to be real. However, I am not sure how gauge invariance would come into the picture to give further contraints. I think the...

The title pretty much covers it. I'm having to calculate the field induced inside the human body by an antenna in the near field (essentially, a phone placed close to a user's head), and I'm drawing a blank on how to relate the field generated by the antenna to the field induced inside the...

Hi, I'm trying to understand what determines whether a plasma will be collisionless or collisional. I understand that a diffuse plasma with large mean free path will be collisionless but I don't really understand it from an electromagnetic point of view

a) $$\phi_T=\phi_F-\phi_I=10^4\cdot 4\cdot 4-10^4\cdot 4\cdot 4=0\, \textrm{Nm}^2/\textrm{C}$$ b) $$\phi_F=\underbrace{300\cdot 4}_{\vec{E}}\cdot \underbrace{4\cdot 4}_{\textrm{area}}=19200\, \textrm{Nm}^2/\textrm{C}$$ $$\phi_0 = 300\cdot 0\cdot 4\cdot 4=0\, \textrm{Nm}^2/\textrm{C}$$ Then...

By measuring angle \theta from the positive ##x## axis counterclockwise as usual, I get ##d\vec{E}=k( (\lambda_2-\lambda_1)\cos(\theta)d\theta, (\lambda_2-\lambda_1)\sin(\theta)d\theta )## and by integrating from ##\theta=0## to ##\theta=\frac{\pi}{2}## I get...

From ##\oint_{\Gamma}\vec{H}\cdot d\vec{l}=\sum I## by Ampere's Law which gives ##H \Delta l=\Delta N\cdot i\Leftrightarrow H=n i## where ##n=## number of turns per unit length so ##i=\frac{H}{n}=\frac{10^3 A / m}{\frac{200}{0.2m}}=1 A##. Since ##\vec{H}=\frac{\vec{B}-\mu_0\vec{M}}{\mu_0}## we...

I considered the capacitor as two capacitors in parallel, so the total capacitance is ##C=C_1+C_2=\frac{\varepsilon_0\varepsilon_1 (A/2)}{d}+\frac{\varepsilon_0\varepsilon_2 (A/2)}{d}=\frac{\varepsilon_0 A}{2d}(\varepsilon_1+\varepsilon_2).## Since the parallel component of the electric field...

Can someone provide more information about this method to measure chracteristic impedance using resistance paper?. Kraus' book claims that the characteristic impedance can be measured by simple dc measurement. It even shows a case to mesure the impedance of a coaxial cable with square outer...

I have thought about the following ##\oint \vec{H}\cdot d\vec{l}=0\Leftrightarrow H_{int}(D-h)+H_{ext}h=0\Leftrightarrow (\frac{B}{\mu_0}-M)(D-h)+\frac{B}{\mu_0}h=0\Leftrightarrow M=\frac{D}{D-h}\frac{B}{\mu_0}## but (supposing what I have done is correct) I don't understand which value of ##B##...

From the graph we see that at ##H=4 kA/m,\ B=1.5T##. We have that ##M=\frac{B}{\mu_0}-H=\frac{1.5T}{\mu_0}-4kA/m## and from Ampere's Law that ##i=\frac{HL}{N}=\frac{4kA/m\cdot 0.1 m}{100}## and the current (density on the surface is) ##\sigma_{m}=M##. Does this make sense? I am having...

I have doubts about the wording of the exercise: (1) energy density is ##u=\varepsilon_0 (cB)^2## but since the question asks for mean energy density should I perhaps average over ##cos^2 (\omega t)## (there due to the ##B^2##) and thus use ##<u>=\frac{1}{2}\varepsilon_0 (cB)^2##? (2) it seems...

Considering a reference frame with ##x=0## at the leftmost point I have for the leftmost piece of wire: ##\int_{x=0}^{x=2R}\frac{\lambda dx}{4\pi\varepsilon_0 (3R-x)}=\frac{\lambda ln(3)}{4\pi\varepsilon_0}##. The potential at O due to the semicircular piece of wire at the center is...

The electric field is the one generated by the charge ##+Q## on the inner sphere of the capacitor, which generates a radial electric field ##\vec{E}=\frac{1}{4\pi\varepsilon_0}\frac{Q}{r^2}\hat{r}## which, due to the presence of the dielectric, become...

In my textbook on EM, the formula for self inductance of a finite solenoid is given as: L= (μ(o)* N^2*A * {√(a^2+ l^2) - a} )/l^2 where a=Radius of each turn, l=length of solenoid. I am having trouble and extreme difficulty in trying to ascertain how this formula was derived in the book and...

B equals 50*10^-7 T (at first instance) Fm equals 8*10^-20 N (at first instance) I know Fm is perpendicular to the velocity, and I know the estimation of the trajectory (somewhat similar to the curve y=lnx). Since I think vertical velocity will be constant, only changing the x component, I...

High! I have a EM plane wave hitting normally a surface dividing universe in media 1 and 2, both without losses. So we have incident, reflected and transmitted waves. It's a simple exercise in which you are given the basic data about two media and wave incident amplitude H in medium 1. I get...

A thin shell in reality doesn't have zero thickness. Consider the image below, showing a cross-section of a small portion of the shell: Here we are considering a more general case in which we have electric fields of magnitude ##E_1## and ##E_2## on each side of the shell. Gauss's Law...

When we connect tungsten filament light bulb to the battery, filament becomes hot due to electrons losing kinetic energy in the electric field inside of conductor. Heat is eventually converted to electromagnetic radiation making light bulb shine. Light energy comes from flow of electrons and...

What am I missing? I also don't get the title of the section: "Charge distributions with enough symmetry for Gauss's Law". I thought Gauss's Law was valid for any closed surface enclosing a charge. I don't understand what "enough symmetry" means in the title above. I get that with symmetry...

Using Gauss's Law By using a symmetry argument, we expect the magnitude of the electric field to be constant on planes parallel to the non-conducting plane. We need to choose a Gaussian surface. A straightforward one is a cylinder, ie a "Gaussian pillbox". The charge enclosed is...

Hey, I was trying to figure out this problem. I got (a) using B = mu * NI/L but I'm not sure how to start the part about the magnetic field in the gap after the solenoid is ripped in half with 1 cm gap. Thanks for the help!

I am interested in particular in the second integral, in the ##\hat{r}## direction. Here is my depiction of the problem: As far as I can tell, due to the symmetry of the problem, this integral should be zero. $$\int_0^R \frac{r^2}{(x^2+r^2)^{3/2}}dr\hat{r}$$ I don't believe I need to...

The strategy will be to figure out what ##dq##, ##\hat{r}_{dq,p}##, and ##r_{dq,p}## are, plug them into the expression for ##d\vec{E}_{p_r}##, then integrate over ##d\vec{E}_{p_r}## to obtain ##\vec{E}_{p_r}##, the electric field at ##P## due to the arc on the right. Then I will repeat the...

Consider two different Taylor expansions. First, let ##f_1(s)=(1+s)^{1/2}## $$f_1'(s)=-\frac{1}{2(1+s^{3/2})}$$ Near ##s=0##, we have the first order Taylor expansion $$f_1(s) \approx 1 - \frac{s}{2}$$ Now consider a different choice for ##f(s)## $$f_2(s)=(1+s^2)^{1/2}$$...

I know what the answers are, because this is all part of the notes from MIT OCW's 8.02 Electromagnetism course. In case you want to see the actual problem, it is example 2.3 that starts on page 18; the limits I am asking about are on page 20. How do I go about calculating the limits? Ie, what...

Hi! So I know about the electron-photon interaction but what about photon-photon interaction? I mean, I do know there is a very small chance for them to interact, but how else do they transfer energy in order to get from Sun to Earth, for example? When it comes to sound waves I get it, for...

In p.385 of Griffiths QM the vector potential ##\textbf{A} = \frac{\Phi}{2\pi r}\hat{\phi}## is chosen for the region outside a long solenoid. However, couldn't we also have chosen a vector potential that is a multiple of this, namely ##\textbf{A} = \alpha \frac{\Phi}{2\pi r} \hat{\phi}## where...

Was there any study of this experiment in the context of classical electromagnetism? It is often claimed that such an experiment is impossible to explain classically, yet, the only classical model I've seen employed is Newtonian mechanics (bullets). The EM fields associated with the electrons...

I have always been interested in learning more about electromagnetism after going through Resnick Halliday Krane 5th edition. Upon reading a few ( read quite a lot) of E&M book threads, I have come to realize that the following texts are often pitched as alternatives to each other: Griffiths...

I was reading this:

Let's say an object far far away from the Earth free falls in gravitational field. At Earth's surface free falling object gains kinetic energy E_1. Let's say an electron far away from the proton free falls in electromagnetic field. At Bohr's radius free falling electron gains kinetic energy E_2...

Interesting thing, the undergraduate courses of electromagnetism states the electromagnetic field caused by electric charge: d∗F=4π/c∗J, and students, in my opinion, mistakenly imagine the electromagnetic field as a product of charged particle. In my opinion, it is more correct to say that...

I know that the resistance of an ohmic conductor increases with length because the electrons going through the conductor must undergo more collisions in a longer conductor. But why decreasing the cross-sectional area of the conductor also increases the resistance of a conductor?

Hi to everyone! I'm currently working on a University project and one of my crazy ideas needs me to get my hands on a pretty strange electromagnet. the measurements are 40cm by 40cm with a height of 3 to 5 cm (doesnt matter a lot) i don't need this magnet to be very powerful (just enough to...

Summary:: Can a moving object cause disruptions in a magnetic field that could be detectable? Hello, I was hoping someone could assist me on a query I have regarding disruptions in a magnetic field. For some context, I am creating a science fiction story which features a non-humanoid alien...

So as the summary suggests, I am studying Electromagnetism, magnetic properties of matter and Magnetization vector in particular. As a first example and to introduce the Magnetization vector (M), my textbook shows a ferromagnetic substance in a uniform magnetic field (B). Then, every atom of...

So it seems the typical way to approach this problem is to consider the sphere when it has charge q and radius r. With uniform charge density ##\rho##, this becomes ##q = 4/3 \pi r^3 \rho## and so ##dq = 4 \pi r^2 dr \rho##. Using our expression for the potential outside of the sphere, we find...

I have encountered two (?) definitions of the electric quadrupole moment. They are: $$Q_{ij}=\frac{1}{2}\int \rho(\vec{x}')x'_i x'_j\,\mathrm{d}^3x'$$ and $$Q_{ij}=\int (3x'_i x'_j-\delta_{ij}x'^2)\rho(\vec{x}')\,\mathrm{d}^3x'$$ I am trying to study radiation arising from the electric...

I've attached a picture of a table in Sean Carroll's The Particle at the End of the Universe. It says that photons don't "feel" electromagnetism, but gluons feel the strong force, the W and Z bosons feel the weak force, and gravitons feel gravitation. How is this so? (I have no formal quantum...

I accelerate charged particle ##A## causing virtual photons to travel to distant charged particle ##B## which feels an electromagnetic force proportional to ##A##'s acceleration (for a classical field description of this effect see https://www.feynmanlectures.caltech.edu/I_28.html Eqn 28.6)...

So my idea was that to reach the equilibrium position, the final moment of force has to be 0 (so in the end the forces will “eliminate” each other). And I found the equation Fm=B*I*l*sinα, which should characterize the force, which affects wire with the current in a magnetic field, and Fleming’s...

We are discussing the introduction to Einstein field equation, so he start talk about the linearity in Newtonian gravity and the non linearity in GR. But there is somethings I am missing: > " (...) in GR the gravitational field couples to itself (...) A nice way to think about this is provided...

Hi I am looking for a textbook that covers most of the topics in a general undergraduate electromagnetics course. It would be great if the topics below are covered. I don't mind getting a few but would like to find a good explanation of these topics. thanks Gauge invariance Lorenz gauge Greens...

I want know is there any unified and consistent theory between general relativity and electromagnetism ? If yes could you provide me any textbook ? I'm interest

Electromagnetism in the atoms is why we can't pass through a bank vault. But supposed electromagnetism were canceled for an object, what would happen to the residual or remaining Pauli Exclusion principle? Would it still cause resistance to passing through the vault? On a second scenerio, what...

Poynting's Theorem (https://en.wikipedia.org/wiki/Poynting's_theorem) says: The rate of energy transfer (per unit volume) from a region of space equals the rate of work done on a charge distribution plus the energy flux leaving that region. $$-\frac{\partial u}{\partial...