Electromagnetic Definition and 1000 Threads

Hi, this looks stupid and simple, but I just can't get my head around it. Assuming a homogeneous medium. The electromagnetic continuity equation goes as ∇⋅J + ∂ρ/∂t = 0 since J = σE, ρ = ɛ∇⋅E, and assuming the time dependence exp(-iωt) we have σ∇⋅E - iωɛ∇⋅E = 0 (σ - iωɛ)∇⋅E = 0 So, σ - iωɛ = 0...

Why are electromagentic waves not visible itself but visible if they are reflected by an object ? Assuming a source of light emitting photons. This waves are not visible in the dark. If they end up on a surface of any object which "reflects" the light we start to see the object. What happens at...

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...

This question is a continuation/topic-extrapolation of: https://www.physicsforums.com/threads/flux-in-magnetic-core-according-to-special-relativity.856482/#post-5374651 My question is 'how is the electromagnetic field different from some sort of mere electric-charge field?' The issue I have...

Is it correct to say a varying electric field creates a magnetic field and vice-versa instead of saying that a charge creates such fields?

Say you have a transmitting whip antenna. If you send a quick DC burst into it, you will get the electrons in the antenna accelerating in one direction like this: If that EM wave is then absorbed by a receiving whip antenna, the electrons will also move in one direction. The polarity of the EM...

I am trying to create a solenoid with a high flux density, but I need the specifications (wire gauge, current applied, etc). The diameter of the core would be preferable around 15mm. The length can be pretty much anything reasonable. I need this for a project that requires a strong repulsive...

Consider the image below Does it emit all 3 types of heat in the form of UV, IR and light? At what threshold does light start to appear and what colors should it illuminate? Hypothetically, say I have an induction furnace and is capable of setting frequencies to about 700THz, will it be able to...

Does electromagnetic radiation emitted by cold hydrogen gas travel at the speed of light?

Homework Statement Problem is as follows: (Figure 1) shows two very large slabs of metal that are parallel and distance l apart. The top and bottom surface of each slab has surface area A. The thickness of each slab is so small in comparison to its lateral dimensions that the surface area...

In my physiology (biological science) class it was explained that, upon eating some food source, some energy is converted into a useful form for the body, and some energy is lost in the form of heat. The lecturer didn't explain what form this heat is in. I thought that 'heat' must be an EM...

hello, I was wondering what caused quantum fluctuations within an electromagnetic field as i recently accepted that there are no virtual particles what causes the energy to fluctuate. here the quantum fluctuations are said to be caused by virtual particles. essentially I'm asking for an...

Hi, I am working on a project where I've to make an electromagnet and very very low amount of current (micro amp to nano amp) will be supplied to the electromagnet. And finally have to measure the magnetic filed with a sensor. My question, is it feasible to generate measurable magnetic field...

I was thinking about a laser, a very strong laser, how does it "burn" things? And what about the microwave oven? What happens in the atomic scale? I know that when something has an increase in temperature the atoms moves quicky because the the temperature is proportional to the kinetic energy...

Homework Statement A small bar magnet is being slowly inserted with constant velocity inside a solenoid as shown in figure. Which graph best represents the relationship between emf induced with time Homework Equations ε = -dφ/dt φ = B.A The Attempt at a Solution Since the magnet is brought...

I am confused with the fact of radiation pressure on Wiki and my homework solution. They are both arguing that the pressure produced by a ray of light to be reflected with incident angle θ and intensity I is: $$\frac{2I\cos^2(\theta)}{c}$$ My thinking We know that: $$Ft=\Delta p$$ We see the...

Hello, first off, I'm not sure if I put this question in the right place so sorry about that. Given Bi = 1/2 εijk Fjk how would you find F in terms of B? I think you multiply through by another Levi-Civita, but then I don't know what to do after that. Any help would much appreciated.

Homework Statement Hi this is my first post I hope that my explanation is good. Now this is the explanation. Now I will provide the known values. So I start looking literature and some formulas to solve this and I found two different propagation constants. Gama and Beta. Homework...

Is this phenomenon explicable with the simple laws of electromagnetism alone?

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...

Homework Statement http://physics.columbia.edu/files/physics/content/Quals2010Sec2.pdf Problem 1 Consider a rigid, ideally conducting sphere of radius R, with total charge zero. The sphere rotates with angular velocity Ω, ΩR<<c. Suppose a dipole magnetic field threads the sphere. the dipole is...

Hello. I'm trying to wrap my head around how Lagrangians work in classical field theory. I have a book that is talking about the gauge invariance of the Lagrangian: \mathscr{L} = -\frac{1}{4}F_{\mu\nu}F^{\mu\nu}-J^\mu A_\mu. It shows that we can replace A^\mu with A^\mu+\partial^\mu\chi for...

I may be asking a ridiculous question and if so, then I apologise. Anyway, if there is an object with a charge of +1 and also another object with a charge of -1, one metre away from the first object, then what is the force between these objects in Newtons? Also is there a way in which to convert...

Homework Statement Calculate electric field and magnetic field produced by radiation emitted by a 100 W bulb at a distance of 1 m if radiation efficiency is only 5%. Homework EquationsThe Attempt at a Solution I only know how to find intensity due to the bulb: I = P/4πr2 = 5/4π W/m2 I have...

Hi there, Over the last couple of weeks, I have been learning about the relativistic description of electromagnetism through Leonard Susskind's Theoretical Minimum lectures, and although I have managed to follow it, there are some parts which I am becoming increasingly confused by, not helped...

Are electric and magnetic fields real or are they just mathematical manipulations? Of course, one could say that we do not care about whether they are real or not, the only thing which matters is that they are useful in describing various things. But we assign quantities like energy, momentum...

Ive been wondering about this for about two days and i have a simple question and that is , if I have two photons that are 180 degrees out of phase, passing through a surface perpendicular to the photons velocity vector then will the EM fields exert tension on the surface?(in this case the...

How would you calculate the energy in an electromagnetic field produced by a particle such as an electron?

Hello, I am trying to find the magnetic field that accompanies a time dependent periodic electric field from Faraday's law. The question states that we should 'set to zero' a time dependent component of the magnetic field which is not determined by Faraday's law. I don't understand what is...

In the same sense that Newtons (N) are the unit for measuring gravitational force, is there a unit for measuring electromagnetic force and if so what is it and what symbol denotes it? Thank you for your help and time!

I am wondering the realistic expectation of a large, rectangular electromagnet, or series of them, to elevate a variable weight. Specifically, can an electromagnet be designed in a 76 inch by 80 inch platform and elevate a plate of the same dimensions that can hold a maximum of 400 pounds...

Homework Statement Using a galvanometer and a coil, we thrust a magnet with a defined north and south pole into the coil and the galvanometer measured the induced current created. Now, depending on how the coil flow(front to back or vice versa) the galvanometer measured an induced current...

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?

Suppose you have a solution to the Maxwell's equations in vacuum, and now you want to find what kind of charge/current system create the wave in the first place, can this be done?

Hi, I am investigating the possibility of using 2 oppositely polarised electromagnetics to locate 2 moving bodies into the correct position as they move towards each other and would appreciate some thoughts on the feasibility of the solution and ways it might be improved. I am proposing using...

Does anyone have any thoughts on what would happen if you tried harnessing Electricity from an Electromagnetic field?

Hi All, I am a EE student and thinking about doing the following classes in Spring 16 - Signals & Systems + Electromagnetic + Physics 3. Any suggestions is Emag and Signal and systems very hard?, what Math do you need? (Dif Eq) Is it a bad a idea taking these classes at the same time...

Hello, This is just a curiosity of mine, after noticing light falling on a metal pendulum while doing a simple pendulum period measure, in the laboratory, using a mathematical pendulum at a small angle. Given that, there is a (very small) effect on the pendulum caused by the light falling...

Homework Statement We take a horizontal copper bar with length of 20cm and attach it from the middle to a vertical spring which mass is neglected and has a spring constant K, we apply a horizontal magnetic field with magnitude 1/2 T and have a 10A current run in the copper bar. The bar rests...

" Thus according to Maxwell, light waves are associated with changing electric and magnetic fields; changing electric field produces a time and space varying magnetic field and a changing magnetic field produces a time and space varying electric field. The changing electric and magnetic fields...

Hi there, I am thinking about an electromagnetic levitation project. Imagine a tube of about 13cm diameter with a flat rotation-symmetrical object of maybe 4cm diameter at one of its ends. The object should be oriented always perpendicular to the vertical tube...difficult to explain as I don't...

Consider a closed electric circuit consisting of a conducting straight rod connected to a DC voltage source switched on. In steady state the current flowing through the conductor creates a steady magnetic field around it with magnetic flux lines that can be represented as concentric circles...

Consider the problem shown in the "wave_incidence_1.png" attached image. An electro-magnetic wave is traveling towards an interface between its current medium and a new medium, which has a refractive index n_2 \neq n_1. The interface is represented by the (x,y) plane. The electric field...

Homework Statement In a certain system of units the electromagnetic stress tensor is given by M_{ij} = E_iE_j + B_i B_j - \frac12 \delta_{ij} ( E_kE_k + B_kB_k) where E_i and B_i are components of the 1-st order tensors representing the electric and magnetic fields \bar{E} and \bar{B}...

I'm studying electromagnetic induction and I'm trying to understand a couple of things: Why is the flux greatest when the angle between the conductor and magnetic field is 90 degrees? How does the induced e.m.f oppose the change which induces it? My thoughts: The flux is greatest when the angle...

As i am a physics amateur and most of what i learned is through videos, i sometimes get confused about energy conservation, my question concerns particle acceleration in CRT for example, we create a potential difference ( which requires energy) between the anode and the cathode, then the...

Homework Statement . A charge 2Q is located at the origin while a second charge -Q is located at x = 1m. Find the position x where a third charge should be placed so that the net force on this charge is zero? Homework EquationsThe Attempt at a Solution I know that the charge must be placed...

Homework Statement Please see the attached file.Homework Equations $$\frac{dΦ}{dt} = ε$$The Attempt at a Solution The only way I see is to apply some conservation of energy. But I don't know how. The potential energy is being converted to rotational energy. But how do I find the potential energy?

Source: http://gmammado.mysite.syr.edu/notes/RN_Metric.pdf Section 2 Page: 2 Eq. (15) The radial component of the magnetic field is given by B_r = g_{11} ε^{01μν} F_{μν} Where does this equation come from? Section 4 Page 3 Similar to the electric charges, the Gauss's flux theorem for the...

In a spherical symmetric problem the only nonzero components of the electric and the magnetic field are Er and Br Why?