Electromagnetic Definition and 1000 Threads

Can light travels without electromagnetic field ? Thanks

$\newcommand{\uvec}[1]{\boldsymbol{\hat{\textbf{#1}}}}$ There is a uniform magnetic field $\mathbf{B}$ directed along the axis, and confined to a cylindrical volume of radius $R$. The magnitude of $\mathbf{B}$ is decreasing at a constant rate of $10$ mT/s. In unit-vector notation, what is the...

I saw a very old post where someone asked where an electron gets it's charge. Where does the charge come from? Doesn't it arise from the interaction with photons? My understanding is that electric charge and magnetism can not exist without photons, and the electron itself most likely could not...

So I can't find this anywhere, but I would really like an answer as it's driving me up a wall; Are the amplitudes of all electromagnetic waves the same, and if so how are the speeds of the particles that move along the wave not > c? Thanks in advance.

Homework Statement Homework Equations That is my solution: The Attempt at a Solution i solve my problem without ø=30°, I confused what this angle was used to do?

What is the smallest amount of electricity (volts, amps?) required in order to create a magnet capable of spinning a 50 grams steel object 150,000 - 200,000 rounds per minute (rpm)? Phrased another way: What is the smallest electrical engine capable of doing that at the present? 50 grams might...

Homework Statement Thin conducting disc, radius a, thickness b and resistivity p (assumed to be large enough induced currents produce no magnetic field). There is a uniform B field B0sin(wt) parallel to its axis. I first had to find the electric field a distance r from the disc axis in the...

Homework Statement Explain the location of the poles of the electromagnet. Homework Equations RHR The Attempt at a Solution Is this correct?or are the poles opposite of what they are meant to be. I believe it is south on the left a confirmation would be great thank you :)

Hello! I am not quite sure how do i verify the complex wave function of EM wave \vec{E}(x,y,z,t)= \vec{E}0ei(kz-\omegat+\delta) is a function of the wave equation \nabla2\vec{E}=\frac{1}{c^2}\frac{∂^2E}{∂t^2}

Hi, In EM theory to derive the 'wave equation for electric field in a conducting medium' we make ρfree to be zero, but we still use σ to be nonzero. My question is why we are doing this ? σ denotes the conductivity of the material and a material can not conduct if it has no free carriers...

Hello everyone. I have a question about waves and how they interact in certain settings. 1.) What happens when two EM waves (of different frequencies and amplitudes) arrive at the same space at the same time, and are traveling 45 degrees to one another? Do their trajectories, amplitudes, and...

Homework Statement the ans is C for this question. i really have no idea , van someone explain please? Homework Equations The Attempt at a Solution

Homework Statement for this question, i only know that E=-L dI/dt... the ans is C , can anyone explain how to get C? Homework Equations The Attempt at a Solution

If you'll allow me to disregard the effects of Strong Interaction, how would I calculate the Electromagnetic Force between two oppositely charged point particles that are in contact with one another? Let's assume two particles with opposite Elementary Charges: 1.60218E-19 and -1.60218E-19 and...

So if an EM waves travels from one medium to the other, it refracts depending on Snell's law. But what happens when it doesn't travel from one to the other, but goes right along the boundary so that one end of the amplitude is in each medium? As the wave "waved", would it have different speeds...

Hi, I have just registered to ask something that I can't find the answer anywhere. As you know, microwaves are absorbed by water molecules because of its shape and angles etc. I wonder which wavelength can be absorbed by nitrogen molecules in the air or at least need to learn a method to...

We have recently begun learning about quantization of the electromagnetic field and I would to understand more. It is tempting to want to connect the number states of a definite momentum and polarization to the concept of a classical plane wave. However it seems less straightforward than I might...

Homework Statement An electromagnetic planewave (non-monochromatic) propagates in vacuum along the positive x axis. The electric field vector is parallel to the y axis. We know the dependence of the component E_y on the variable x at the moment t = 0: E_y(x) = E_0\ \text{if}\ |x + a| < b...

Homework Statement The contour consists of a condenser with capacitance C = 2.22*10^-9 F and a coil of copper wire. The diameter of the wire 5*10^-4 m, the length of the coil 20*10^-2 m. Determine the damping logarithmic decrement Λ of the fluctuations? Given answer:0.018 Homework Equations...

I have a solid foundational understanding of far field electromagnetic radiation i.e., two in phase electric and magnetic fields oscilating perpendicular to each other and to the direction of wave propagation. However, I have some ambiguities regarding near field electromagnetic radiation and...

Homework Statement Let F1,F2 and F3 be the forces experiences by a test charge q at a point in a region of electric and magnetic fields E and B, respectively, for velocities v1,v2 and v3, respectively, of the charge. If F1,F2 and F3 are such that A= F1xF2 + F2xF3 + F3xF1 =/= 0, that is, their...

Can you make an educated guess on the amount of energy in the universe in the form of electromagnetic radiation (photons), considering the vast amount of photons moving in every direction throughout the vast universe, there is literally no point in the universe that you can be in and not observe...

Homework Statement A 425 mA conventional current is induced in a 48.0cm wire moved through a magnetic field. A 11.5 Ω resistor is connected to the wire as shown in the diagram below. If the magnetic force acting on the wire is 323 mN, then determine the direction and magnitude of the velocity...

Capacitors are popular candidates for explaining electric fields. The phenomenon becomes really apparent with the aid of a leiden jar ...which is really just a capacitor. Anyways, as long as you're cranking the handle on the electrostatic machine, the charge is going to build and build until I...

The electromagnetic spectrum contains wavelengths that are on the scale of macroscopic objects. What I'm not sure about then is, does this mean that photons corresponding to these "macroscopic" wavelengths are actually that size? My guess is that these photons have a corresponding electric field...

Homework Statement Question 1. General Plane Waves. We may represent a general electromagnetic plane wave by (real part of the complex exponentials) E=E_{0}*e^(i*k*r-iwt) B=B_{0}*e^(i*k*r-iwt) Show that Faraday's Law becomes iwB0=-ik x Eo Homework Equations dB/dt=- curl of E The...

Hello, I know the magnetic field produced by a direct current flowing through a solenoid has a north and south pole, so how about the magnetic field produced by a current flowing through a straight conductor, does it have a north and south pole too? If it have them, where is it located? A...

Homework Statement Consider a spherical dielectric shell so that ε = ε_0ε_r for a < r < b and ε = ε_0 for 0 < r < a. If a charge Q is placed at the center of the shell, find a) P for a < r < b b) ρ_pv for a < r b c) ρ_ps at r = a and r = b Homework Equations ρ_pv = -div(P) ρ_ps = P...

In classical physics, charged particles induce electric field ##\vec{E}_c## around them. How do we interpret this classical electric field ##\vec{E}## in quantum mechanics. Is this just the vacuum expectation value ##\vec{E}_c=<0|\vec{E}|0>##? if so, it means ##<A>\neq 0##. This would lead to...

Hi, sorry if this has been asked before. It is known that two parallel wires carrying electric currents in the same direction attract one another. The force is known as electromagnetic force. My question is whether this has been checked for two pure currents of charges. Specifically, whether...

I'm reading about electromagnetic waves and I can't make sense of their self-sustaining nature. If a charge accelerates for a moment and then stops a disturbance in the electric field is sent out. This changing electric field creates a changing magnetic field and they continue to sustain each...

I am interested to know if a copper coil wrapped around a iron pipe could be used to propel another iron pipe capped at both ends through the larger pipe with the copper coil around it? I am thinking that the larger iron pipe would need to be slotted from end to end and insulated from the...

If you don't have any charges or currents, the electromagnetic Lagrangian becomes ##\mathcal{L}=-\frac{1}{4}F_{\alpha\beta}F^{\alpha\beta}##. The standard way to derive Maxwell's equations in free space is to replace ##F_{\alpha\beta}## by ##\partial_\alpha A_\beta -\partial_\beta A_\alpha## and...

Hello, I'm stuck on this question, and it's really annoying me. I scanned the page so it has a bit more context. It's question 3.7: "A long wire carrying a steady current is placed in a uniform magnetic field parallel to it's own length. What is the shape of the magnetic field lines...

Hi Guys, Your previous insights on the thread regarding gravitational rod shortening along the radial axis really helped me to have a naive but practical idea of what GR is about. The next step in my thought process seems to be whether the EM force could induce rod shortening. The force...

Hi all, can the angular frequency of a electric waves be used to determine the wavelength using the following; ω=2πf rearranging for the frequency, and using the following; E=hf=(hc/λ) or can this formula no be used as it is dealing with photons?

Since we can observe gravitational lensing and conclude that mass can affect the path of EM radiation it seems logical to me to assume that EM radiation will exert a slight gravitational attraction of it's own on a mass,- although I do not recall ever reading about this. Presumably the...

While I get the coherent and incoherent scattering process that leads to the bragg diffraction condition, I don't really understand the physical mechanism behind the transmission and reflection. Now, as I understand it, the bragg diffraction condition is satisfied only for one or two particular...

Is it true that the energy in electromagnetic waves can only be released in "packets" of energy? Or is this only the case for a system where a standing wave change from one mode to another which results in sending out an electromagnetic wave (photon). In other words if I ride on my bike...

First of all, I'm not sure if this thread belongs here or at the "Special & General Relativity" sub-forum, if I posted at the wrong place please move it. Homework Statement I encountered this problem working in my master's degree. I need to find the stress-energy tensor of the following...

Does the law of the conservation of energy apply to the light in our universe? If yes, is our universe a closed system? If no, is our universe losing energy?

Homework Statement First off: these are not homework problems technically, I'm doing these for my own benefit...they're not being graded or collected. Just trying to study for my final. Problem 1 A thin spherical, conducting metal shell has a radius of 15.0cm. A positive charge of 1.30µC...

Hello there! This is my first post here, hopefully I am not posting in the wrong place. Also, I am an engineer and have not used this stuff for years, so please be patient with me, I am pretty sure that my question is stupid :-) I would like to develop a simulation code for charged particles...

When we have a current in a long wire, what is the kind of total energy of the system? We do have an electric field inside the wire and a magnetic field outside it. I think the electric field has an energy, say E, and it is only this energy which appears also as magnetic energy and we don't have...

Homework Statement A wire of length L=20cm travels with an acceleration a=0.002m/s2 perpendicular to the Earth's magnetic field (B=20μT). Considering that the wire starts from rest, calculate the value of the emf (electromagnetic force) when an hour has gone by. Homework Equations My...

So the other day I posted about designing an electromagnetic toy for my physics class project (https://www.physicsforums.com/showthread.php?t=726492). Unfortunately, where I live, finding disc magnets with conductive plating, is like really finding that needle in a very very big hay stack...

Hi all, I am looking at the possibility of creating a large magnetic jig for making up wiring harnesses. Currently we use wooden boards 2400 x 1200mm and simply put a full size drawing of the wiring harness on it and bang in nails. Although this is OK for some harnesses it is not ideal. We...

That is being done for my final project. I am following this concept: http://sci-toys.com/scitoys/scitoys/electro/railgun/railgun.html With the aluminum strips and thinking of making a race car and placing it on it. Now, would there be any restrictions on designing a race car with 4...

What are the three forces responsible for a neodymium magnet to fall slowly down through a heavy copper tube?

Obviously it makes sense when considering the force of weight and the fact that the object is not moving up or down, but what is it composed of? What I mean is, the ground you are standing on is made of molecules bonded through the electromagnetic force, right? But those bonds are parallel to...