Em waves Definition and 234 Threads

I am not looking for formulas or references to theories... this is just a general question about how to visualize/explain EM waves. Are EM waves such as light, radio waves, etc. really more like pulses and we just measure their intensity from a static point as a wave line? I thought I...

If EM waves create gravitational field "around" them (as I understand is the case) which reference frame we should use? We could imagine several observers, some moving in the same direction with EM wave with different speeds, others moving in the opposite direction. The different observers...

Hi! I try to get some intuitive understanding on the equipartition theorem stating that in thermal equilibrium, energy is evenly distributed among all degrees of freedom of a physical system. This is indeed intuitive for a system consisting of composite particles with translational and...

Hi all, I've got a quick clarification question. Generally when the production of electromagnetic waves are discussed, it's done in the context of an accelerating electric charge. Is it possible to generate EM waves by instead accelerating something like a permanent magnet? I.e. if I wiggle a...

Hi, I have a few question about EM waves. What is an EM wave composed of? Are the E and B field lines real or imaginary. .. if it is an wave what is waving? (Eg water is waving in tsunami) wouldn't a pulsating chargr produce a electric pressure wave?

Homework Statement I'm working on using the wave equation to prove that EM waves are light. Homework Equations Here's what I'm working with: E = Em sin(kx-wt) B = Bm sin(kx-wt) ∂E/∂x = -∂B/∂t -∂B/∂x = μ0ε0 ∂E/∂t and the wave equation: ∂2y/∂x2 = 1/v^2(∂2y/∂t2) The Attempt...

Hey, I'm new here but I was hoping you guys could help me out. I am currently studying Waves mainly using MIT's course 8.03 - Vibrations & Waves. I am now at a point where I have almost finished reading AP French and entering EM Waves. Unfortunately French decided (for whatever reason) to not...

Mechanical waves (sound, water waves) and EM waves both undergo diffraction. But the actual physical processes involved in the two are totally different. EM waves are produced by accelerated charges while mechanical waves are tiny displacements of molecules of the medium in which the wave is...

I saw an example of a hypothetical EM wave that had constant E and B fields. Is that possible? How would it be produced? And wouldn't such a wave have an infinite wavelength?

Hi, I've read that the speed of em waves in the vacuum is the electric field component frac the magnetic field component, why and how can this be explained more easily ? Thanks

Homework Statement An EM wave with frequency 87Mhz travels in an insulating ferromagnetic material with \mu_0 \mu_r = 1000 and \epsilon_0 \epsilon_r = 10 - What is the speed of the EM wave in the material. Homework Equations v=(\sqrt{\mu_0 \mu_r \epsilon_0 \epsilon_r})^{-1} The Attempt at a...

why all EM waves are sinusoidal ? or this is not true at all, i.e., EM waves of other waveforms do exist ? the above 2 questions are among the most vague in classical EM theory, of which i studied many topics in collage as an electrical engineering student, and i liked the subject so i kept...

The Drude model of electrical conduction has the charge carriers being accelerated by an electric field and then interacting with the lattice ions. The cycle is then repeated. An unbound charged particle if accelerated emits electromagnetic waves. Does that mean that a prediction of the Drude...

Would a particle kept in the path of an electromagnetic wave experience a force? Both magnetic and electric field are present, so the equation of motion may be complex, but i have never seen my textbook refer to the the possibility of an em wave causing a charged particle to move.

EM waves do not need a medium for propagation. But isn't high frequency signal (like USB) flowing in a wire also electromagnetic. How come it needs copper as a medium.

Hi, recently I saw a great video about some scientists levitating small objects in mid air by trapping them in overlapping 180 degrees out of phase sine waveforms. It is easy to see that air is the medium through which sound can travel and sounditself being the vibration of air traps these...

Homework Statement EM Waves propagating through vacuum towards the x-direction approaches a conducting surface at x = 0. Part (a): Prove the following relations. Find the boundary conditions for E and B if charge density σ and current density s exists on the surface. Part (b): Find B in...

Homework Statement (a) Find the capacitance per unit length and find the inductance per unit length of a transmission wire above a infinite conducting plane. I used the image method (b) Show that EM waves can propagate, and find their speed and the characteristic impedance of the line...

Homework Statement Look at the Moire pattern in "Oppgave 5" (assignment 5) in the attached pdf file. The Moire pattern you see is supposed to represent the interference between two plane EM waves whose directional ##\vec{k}## vectors form an angle ##\theta## with each other. Anyway, the main...

Homework Statement The following dispersion relation is obtained by substituting a plane wave solution for ##\mathbf{B}## into $$\nabla^2 \mathbf{B} = \mu \epsilon \frac{\partial^2 \mathbf{B}}{\partial^2 t} + \mu \sigma \frac{\partial \mathbf{B}}{\partial t}:$$ $$\hat{k} = (\mu \epsilon w^2 +...

First of all, I understand that an EM wave is created by a charged particle that is moving. What I don't understand is how it propagates itself when traveling through a vacuum as there is no medium for it to interact with. Can this be explained by anything other than photon theory? I really...

Do quarks cause EM waves?

Hello, I was reading articles about EMR and health and I realized I never got how "output power" is related to frequency. Let's talk about energy, the rule is: the higher the frequency (shorter wavelength) the higher is the energy transported by the wave. Now power, power is the energy...

Do we have any understanding as to why em waves have same speed in all inertial frames?

Homework Statement A plane polarized electromagnetic wave propagates with Erms = 30 V/m. What is the power transmitted to a circular disk of radius r = 2m, if all of the light is absorbed by the disk and S is perpendicular to the disk? Homework Equations There is a passage that goes...

I've been given a practice question for an exam and I can't quite get it started. The question is: Intelligent beings on a distant planet try and communicate with Earth by sending powerful radio waves swept in frequency from 10 to 50MHz per minute. The linearly polarized emissions must pass...

A moving charge creates a Bf so is an EM wave created (for example) by an electron oscillating in a conductor producing a changing Bf which then induces an Ef with both perpendicular to the direction of propagation? If so I am presuming the point where the Bf crosses the axis represents the...

If the universe is expanding at less than the speed of light, what happens to EM radiation that is emitted from stars at the edge of the universe?

What I'm wondering is whether or not the E-fields and B-fields making up an EM wave always point outwards. Would it be possible to have an EM wave where either the E-fields or B-fields, or both, point inwards towards the path of propagation? The only diagrams I see in books and the internet...

I was reading an article about Cherenkov radiation in wikipedia. If the electron moves slower than light the EM waves in the medium are destructive and if they travel faster than light waves are constructive .Why so?When the electron travels faster than light the radiations cannot interfere...

Sorry if this is in the wrong place. Was not sure what it is categorised as. I have come across the following:e^{-\frac{\omega}{c} nkz}, referring to attenuation of a wave. It was found here...

I'm a little unsure of my own answers to these questions. Hopefully I'll clear up my misconceptions. 1. If I measure the E-field and B-field at a point in space where there is an EM wave, would I be able to determine the direction it propagates from? My Ans: I don't think so, since when...

The interaction of light with matter, or EM waves in general, falls into 3 categories: transparent where they pass through, opaque where they are scattered, and shiny where they are reflected. What on the quantum mechanical level about the atoms electrons determines those properties? I think the...

Hello all, I had a question about Electromagnetic waves. Although it isn’t homework (just to settle something in my own mind) I thought this would be the best place to put it. Perhaps it would be best if I could explain a situation I could understand and then hopefully someone could bridge...

Homework Statement Our prof has told us we can get help from wherever/whoever we want as long as it isn't classmates. This is a take-home test. The relevant question: You have a three-layer dielectric. | Layer 1 | Layer 2 | Layer 3 | Layers 1 and 3 are semi-infinite. Layer 1 is air (εr =...

Hi all, I was just wondering if there has been research into computing using electromagnetic waves. It seems to me like a sealed off box with internal EM pluses could be used to mould waveforms through interference, which would act as logic gates to provide useful computational results. Would...

Homework Statement A rectangular metal plate measures 0.20 m long and 0.3 m wide. The plate is heated to a temperature of 1,433 K by passing a current through it. Assuming that it behaves like a blackbody, how much power does the plate radiate under these conditions? Homework Equations...

Homework Statement Moving in negative x-axis: E1 = E sin(wt + kx) Moving in right axis: E2 = Esin(wt-kx-θ) moving to right write complex representation The Attempt at a Solution E1= E Im(exp[i*(wt+kx)]) E2= E Im(exp[i*(wt-kx-θ)]) are these correct or do I have to take into...

Hi there, I'm stuck with this problem, I've already worked out some algebra but I can't seem to get what I am asked, when trying to solve the equations I simply can't get the answer, so I was hoping you could help me. Here we go Homework Statement Calculate the transmission coefficient T...

When the mic hears the noise, it creates an alternating current electrical signal right? So how does that translate to em waves? Is it just that a higher frequency radio wave length would resemble a higher pitch? If so, is it impossible to hear the pitch "produced" by, say, visible light?

Other than nearby light pollution. Or is that the only reason?

My book seems to not go into a lot of details as to how EM-waves are created. More or less they just state that they are created by accelerated charges. I guess that somehow makes sense since an accelerated charge is clearly altering the electric field everywhere in space and that is as far as I...

I read that speed is directly proportional to wavelength in a medium. so does it mean that gamma is the slowest in air compared to the rest of the waves?

Is it possible (and practical) to use electromagnetic waves to heat copper (or other metals such as iron, steel or an aluminium alloy) over long distances (such as 1km)?

I was wondering, if two EM waves of the same freq could add via superposition ON THE SAME ELECTRON or atom (at the same time) to become ionizing? For argument's sake say if each wave was just below UV I remember E = hf, which would indicate no, I don't see how the energy would not add...

I know that if you have alternating current in a wire, it will produce electromagnetic waves since the electric and magnetic field change direction continuously as the wave propagates, and that the wave direction, orientation of the E component, and orientation of the B component will all be...

Homework Statement You and a friend are sitting in the outfield bleachers of a baseball park 140m from homeplate. The temperature is 20*C. YOur friend is listening to radio comentary with headphones while watching. There is a microphone located 17m from home plate to pick up the sound as the...

I am assuming the answer to my question is no, but what am I missing? My reasoning is very basic: E=hf, therefore as the universe expands the wavelength of all the far traveling radiation is increased and due to constant velocity c their frequency must decrease which translates into them losing...

So, I have been doing a lot of reading. I have an 8 year old girl that has renewed my interest in physics, chemistry, biology, etc. I find it interesting that we say that Electromagnetic Waves travel through a vacum. We know that mechanical waves like those propagated in liquids and gas...

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...