Em Definition and 1000 Threads

How can I find the induced current density by EM wave in a material? Should I have ma = Fbinding + Fdriving + Fdamping like treating it as a spring? Then the current density should be charge density of the material x velocity (ρv), isn't it? Is there any condition the EM wave cannot...

Homework Statement A 50cm wavelength EM wave in air has 50mW/m^2 of energy. what is the frequency? what is the average E field? What is the B field strength? What would be the λ in water? Homework Equations I found the λ. How do I find it in water The Attempt at a Solution...

Homework Statement Homework Equations Savg = Em * Bm / (2*μ0 * c) The Attempt at a Solution I solved for S avg without calculating inside the cos, but I got it right. The z and t is given, but is there the reason why you don't solve inside the cos, or is it the bug? it's...

The setup: I am reading the review: arXiv:hep-th/0004098 (page 9-10). In Einstein-Maxwell theory, the gravitational field equations read: \begin{equation} R_{\mu \nu} - \frac{1}{2} g_{\mu \nu} R = \kappa^2 \left( F_{\mu \rho} F^{\rho}_{\;\;\nu} - \frac{1}{4} g_{\mu \nu} F_{\rho \sigma}...

Homework Statement Hi In Griffiths (chapter 9) he states that any wave can be expressed as a linear combination of sinusoidal waves, f(z,t)=\int_{-\infty}^{\infty}{A(k)e^{i(kz-\omega t)}dk} = e^{-i\omega t}\int_{-\infty}^{\infty}{A(k)e^{ikz}dk} Is it correct to say that this in principle...

Hi all, I've a hamiltonian that describes the coupling of electrons in a crystal (bloch electrons) to an EM field described by a vector potential A \begin{equation} \mathscr{H} = \frac{e}{mc}\left[\mathbf{p}(-\mathbf{k}) \cdot \mathbf{A}(\mathbf{k}, \omega)\right] \end{equation}...

Why is a magnetic field "a field-of-force in space" while a gravitiational field is "not a field in space, but a curvature of space itself"? Why can't we describe and explain EM repulsion and attraction the way we explain gravitational attraction? Why don't we say that the presence of a charge...

It is my understanding that electromagnetic radiation is absorbed by an electron and then emitted at another angle. So why does particle size affect scattering when the phenomenon involves electrons? Also, why does the size of the wavelength of the light relative to the diameter of the particle...

Maxwell's equations use four dimensions. But wouldn't we need more dimensions to completely describe the EM force. I'm thinking of polarization and twist. So how many mathematical dimensions are necessary for a complete description? That is, how big do the matrices need to be and how many...

B=Boexp[-(kz-ωt)2)] i(hat) Calculate the electric field associated with the above magnetic field pulse. Calculate the Poynting vector for the EM field and the total energy per unit area. Use Maxwell's equations in vacuum and assume electric potential is zero. Homework Equations...

Alternating current produces EM Wave. What determines the frequency(or wave length) of an EM wave related to current or voltage?

Hi I don't understand the polarization of EM waves. I have same questions about that. 1-) As you know, EM wave is consist of both electric and magnetic field/wave. And there is 90 degree between them. Is that possible to separate these two fields or waves? I mean is that rule: If there is...

Homework Statement Show that in vacuum the magnitude of the momentum density vector of a plane electromagnetic wave is equal to the energy density divided by the speed of light, c. Homework Equations \vec{S} = \vec{E}x\vec{H} The Attempt at a Solution This doesn't seem too hard if you know...

I was just reading about EM wave propagation and had two questions I would appreciate an answer to. 1-I read how the electric and magnetic fields of an EM wave oscillate sinusoidally and perpendicular to each other and the direction the wave is traveling. Is there any significance or special...

Hello: I was under the impression that gauge symmetry was a property of the Lagrange density. Here is the Lagrangian for EM written out in its components: \begin{align*} \mathcal{L}_{EM} &= J\cdot A +\frac{1}{2}\left(B^2-E^2\right) \quad eq.~1\\ &=\rho \phi - Jx Ax - Jy Ay - Jz Az \\...

Can radio waves penetrate steel? What about titanium? Maybe a characterization of what they can't penetrate would be more informative? ...Or a way to figure out what materials they can penetrate. Thanks, Jake

Homework Statement The plastic rod of the length L=1 m has a non-uniform charge density λ=cx where positive constant c =2x10-6 [some unit]. What unit does c have? Find the electric potential at the point on the x-axis 1 m to the left from the left end of the rod. Find the electric...

Homework Statement Hi I wish to Fourier transform the following expression P(t) = \int\limits_{ - \infty }^\infty {dt_1 dt_2 \chi (t - t_1 ,t - t_2 )E(t_1 )E(t_2 )} What I do is the following \int\limits_{ - \infty }^\infty {P(\omega )e^{ - i\omega t} } = \int\limits_{ -...

Homework Statement Given the following EM wave propagating in vacuum, find the direction along which the electric field oscillates and the direction of propagation of the wave: \vec{E} = (-3\hat{i} + 3\sqrt{3}\hat{j}) 10^4 e^{i[\frac{\pi}{3} (\sqrt{5}x + \sqrt{5/3} y10^7 - 8.1246 *10^{15} t]}...

When I studied EM we always treated EM fields as being "individual" autonomous fields generated either from the separation of charges or induced by other phenomena. However, I'm reading that modern physics is treating the zero-point energy as fluctuations in THE EM field. Susskind clearly states...

Let's say there is a conducting plane of conductivity \sigma. Boundary conditions for above and below such plane are: E_1^t = E_2^t (D_2 - D_1 ) \cdot n = \rho i.e. tangential components of E field are continuous and perpendicular components of D are discontinuous because of surface charge...

Assuming, of course, that we simply rescaled our color perspectives so that longest wavelengths = red, shortest wavelengths = violet. Are there any such pictures?

Homework Statement two long cylinders (radii a and b) are separated by material of conductivity (sigma). if they are maintained at a potential difference V, what current flows from one to the other, in a length L? Homework Equations Please see the attachment The Attempt at a Solution...

Suppose you have two coherent microwave beams, one beam at 45 degrees to a reflecting wall and the other one at 90 degrees, with the two beams pointing to the same point on the wall. If the two beams are 180 degrees out of phase and destructively interfere at the point on the wall, will the...

Homework Statement A particle of mass m and charge q is attached to a spring with force constant k, hanging from the ceiling. Its equilibrium position is a distance h above the floor. It is pulled down a distance d below equilibrium and released, at time t = 0; Under the usual assumptions...

When an EM wave goes in a conductor it says that the B field component lags the E field component, What causes this? I looked in Griffiths and I couldn't find the answer. Does it have something to do with the fact that when the EM wave enters the conductor it is moving the free electrons in the...

I was always told that EM radiation is a far field effect. Does this mean that the light emitted from the accelerating electron is not right next to the electron but a little further out. And also how do you calculate the frequency of the light coming off. When I looked through Griffiths...

I understand the classical view of EM fields as being (theoretically) continuous. What I don't quite get is how this can be reconciled with the QM view of photons coming only in fixed frequencies (The electromagnetic field may be thought of in a more 'coarse' way.). Is the number of possible...

When an accelerated charged particle is shot into an electromagnetic field such that the accelerated particle comes to a complete stop in the field, we naturally have loss of energy from the charged particle. But what is this energy converted to? And where? Does the particle release radiation...

¿ Can diff. EM frequencies create diff. magnetic fields with diff. properties ? I understand that a magnetic field is generated via moving charged particles . Electricity and magnetism are linked through electromagnetism . Electromagnetism can be in different wavelengths and frequencies but...

I would like to know whether Kelvin or KJs matter when it comes down to a material radiating and / or conducting its heat.

why electromagnetic waves are represented by complex numbers?

The cytoskeletal structures were considered responsible for the elementary cellular intelligence in the past. (For example, see the articles from Albrecht Buehler. http://www.basic.northwestern.edu/g-buehler/FRAME.HTM.) Microtubules are pipe-like structures made of two kinds of proteins...

I am an ameteur physicist (i actually have my degree in meteorology), and i have some questions about the EM properties of liquid metals or ferrous liquids when in spherical form. I understand if you are too busy or if i sound off, but if you do have the time to answer a few questions, it would...

Hi all, I know that the electric field generated by a dipole is given by \mathbf{E}= [1-i(\omega/c) r]\frac{3 (\mathbf{p}\cdot\mathbf{r})\mathbf{r}-\mathbf{p} }{r^3}+(\omega/c)^2\frac{\mathbf{p}-(\mathbf{p}\cdot\mathbf{r})\mathbf{r}}{r} e^{i(\omega/c)r} where \mathbf{p} is the dipole's...

Homework Statement Show that the electromagnetic wave equation \frac{\partial^{2}\phi}{\partial x^{2}} + \frac{\partial^{2}\phi}{\partial y^{2}} + \frac{\partial^{2}\phi}{\partial z^{2}} - \frac{1}{c^2}\frac{\partial^{2} \phi}{\partial t^2} is invariant under a Lorentz transformation...

In another recent thread it was being discussed whether there is energy in the field of an electron according to U = \frac{1}{2}\epsilon_0 E^2. I began by saying "yes", then changed to "no" because of the way the equation was derived. (It was derived by bringing together N=2 or more charges...

Why does a moving particle particle emit EM-radiation?

is it possible to make am em wave of length 5(lamda)...lamda=wavelength of em wave...

Assume a infinite depth good conductor block with width in y and length in x direction. Boundary is at z=0 and air is at z=-ve and conductor at z=+ve. Let a voltage apply across the length of the block in x direction so a current density established in +ve x direction. We want to look at the EM...

My understanding from the book about EM wave that E and B is perpendicular to the direction of propagation only in medium that is charge free so \nabla \cdot \vec E = 0. What cases when E and B not perpendicular to the direction of propagation? Thanks Alan

I just noticed that we tend to call EM wavelengths shorter than visible light "rays" while we call we call those that are longer "waves". Why is that? Did we ever think that "rays" and "waves" were physically different?

If photons "carry" visible light, and light is just a specific frequency of EM radiation... who carries radio waves? [PLAIN]http://www.antonine-education.co.uk/physics_gcse/Unit_1/Topic_5/em_spectrum.jpg And can an EM radiation at specific frequency be changed to a different frequency? I...

Organisms radiation EM energy. I am aware of the brain and nervous system as a source (because of electrical currents, etc) and that we have a lot of IR radiation. Is the majority of the energy due to blackbody radiation, a by-product of chemical reactions, or something else?

Okay I have a really odd question that might be difficult to answer. I have searched for an answer in several physics books and websites and don't think I have come across a specific answer for this question. Suppose I were to send a negative electromagnetic charge through a solenoid and want...

Since a changing current creates a magnetic field, and if there's a wire near by, the magnetic field will induce a current in that wire. What is needed / what does it take to turn that magnetic field into EM radiation such as a radio wave? Or is it purely just the frequency of the current, so...

OK, so recently I have learned that in the early 20th century, while Max Planck was attempting to explain the quantum nature of light, two men named Philip Lenard and Heinrich Hertz discovered the photoelectric effect. They found that an electron must absorb a specific amount of energy...

Can anyone explain why cranes in construction sometimes experience induced currents from antennas radiating from distances of up to several Kilometers. I have looked into the phenomenon several times, and have not been able to find a study or baselines to follow. I have a basic understanding...

Hi, From what I've learned so far, Lorentz transformation meets certain criteria, such as the constancy of EM wave propagation speed in vacuum, &/ casuality, among others. My question is, why would it/would it not be applicable to phenomena that have nothing to do with EM interaction? In...

Hi there PF How does on calculate the field strenght of the electromagnetic field (from Maxwells equations) and of the gravitational field (from general relativity). I want to relate this to particle physics, where the relative strenghts of the fundamental interactions are calculated here...