Em waves Definition and 226 Threads

My father-in-law uses a USB internet stick for his internet since he lives in The Middle of Nowhere where there is no cable nor DSL. His problem is that reception from his basement office is very poor. However, reception from the second floor of his house is okay... I don't understand this...

Homework Statement The helium-neon lasers that we use in lab produce light waves with an average power of 0.85 mW. Suppose that at a distance of 1.0 m from the laser the beam has a diameter of 1.1 mm. a) What is the average intensity of the laser beam 1.0 m from the laser? b) What is the...

The instantaneous energy density of a region of space of an EM wave is: u = \epsilon0E2 [J/m^3] hence the average energy density is: uavg = (1/2)\epsilon0E02 [J/m^3] uavg = <S> / c [J/m^3] Is this equal to the wave's average http://en.wikipedia.org/wiki/Radiation_pressure"...

When I read about Fresnel equations, I see that it is based on boundary equations determined by Maxwell's equations. So I would think these equations only apply to EM waves. But is there a similar behavior in other waves like sound waves in water? Would I want to use or modify Fresnel...

Homework Statement Re‐write the formula E = Eo cos (k• r −ωt) for each of the three waves, in terms of the angles θi, θr and θt and the dielectric constants ni and nt (for the materials on the left and the right) in place of k The incident wave is in the xy plane only as is therefore...

Homework Statement A star is moving away from Earth at a speed of 2.4 x 10^8 m/s. Light of wavelength 480 nm is emitted by the star. What is the wavelength as measured by an Earth observer?Homework Equations fo=fs(1 - vrel/c) I substracted because they the star is moving away from the earth...

If you held frequency constant, and changed the amplitude of EM waves coming from a source, then would the distance into a material the EM waves would penetrate change?

Electricity and magnetism had been unified under Maxwell's four famous equations. But I wonder if there any method to separate the this two components from an EM wave? Will there be any effects if this two components are separated? Hope you all can help me to solve this problem^^ Thank...

Hi, I have been reading my textbook and online but I'm not sure if I understand. An EM wave attenuates in a conductor but not in a dielectric? If that is correct what does the impedance of a dielectric represent, since I thought impedance would be associated with an energy loss...

When an EM wave has a higher frequency, it is able to penetrate materials more easily. However, why does a microwave able to penetrate haze while visible light can't? Why visible light is able to enter our atmosphere while those of gamma can't?

Hi Everyone! I'm new here and like this forum. Can anyone tell me how the electron moving roundly in atom doesn't emit EM waves while changing it's speed?

Hi, I'm having difficulty understanding exactly how the reciever loop detects the EM waves in this experiment and I can't find any definitive information online. My understanding is that since EM waves are transverse, to be absorbed by the receiving electrodes, the length of the molecule chains...

Homework Statement Describe the sum of two EM waves that have the same initial phase and same amplitude but different frequencies such that \omega _1 >> \omega _2.Homework Equations E=E_0 \cos (kx -\omega t + \alpha).The Attempt at a Solution I summed them up and reached, after an...

Homework Statement Show that the superposition of three waves with frequencies \omega _c, \omega _c + \omega _m and \omega _c - \omega _ m and same amplitude are equivalent to another wave of frequency \omega _c which is modulated by a sinusoidal wave with frequency \omega _m, i.e. E=E_0 \left...

In the case of plane waves, E is orthogonal to B and they're both orthogonal to the direction of propagation, call it k. I'm not sure I'm picturing well what such an EM wave is. For instance I know that E and B oscillates with respect to time. Without looking to quantum electrodynamics that...

In general the electronic susceptibility, χ, is a function of frequency and is complex for a dielectric medium. So what are the implications of this for the propagation of EM signals in a dielectric medium? Since the electronic susceptibility varies with refractive index, and the refractive...

Hello. Just a noob question about electromagnetic waves. An electron "wiggles" and sends out a change in electric field, which creates a change in magnetic field, which creates a change in electric field etc etc. My question is, because the photon travels to virtually infinite distances...

I know for spherical or plane EM wave, there's relation E=cB, and we can prove it by the explicit expression of these two kinds of wave. But does E=cB hold for all EM waves, e.g. all possible wavelike solutions of maxwell's equation?

What is the difference between EM Waves and EM Pulses and how are they related to one another? When trying to look up info on this, I always get a full article on either just one or the other so that no comparison is ever made between one and the other, the definitions alone seem a little...

Can man-made EM waves produce physical vibrations of objects? Can man-made EM waves vibrate powders like sand or talc? I'm trying to understand if any types of electronic frequencies can cause physical vibrations...thanks.

I've been trying to search for this seminal paper on EM waves in stratified media. 'Investigations on the propagation of sinusoidal electromagnetic waves in stratified media', by F. Abeles Ann. Phys. (Paris) 5, 596, 706 (1950). I cannot find it in any database. Can anyone please tell me...

Let's assume that electron is moving around the unit circle. Using Maxwell equations show what is the frequency of radiating EM waves. How to start with it? What's the form of known variables - current density and charge density?

Please see the diagram attached, I don't understand how my lecturer is resolving the E-field in the perpendicular case. He obtains: E_i = \bold{y} e^{-i\omega(t - \frac{n_1}{c} (-xsin \theta_i - z cos \theta_i))} How has he obtained the (-xsin \theta_i - z cos \theta_i) part from that...

I'm having some trouble understanding this module. It would be great if anyone could help. In a homogeneous nonconduction region where μr = 1, find εr and ω if E=30(pi)e[i(ωt-4/3y)] in z direction H=0.1e[i(ωt-4/3y)] in x direction I am to understand that for a homognous nonconduction region...

So in a DC current we have a relative uniform movement of electrons in one direction. If we would have a very narrow coil around the dc current carrying wire, (like an atom wide), every time an electron pass trough the plan of the coil, should induce a voltage in the coil, so theoretically we...

Can EM waves falling on a solid contribute towards lattice vibrations? If yes, then i)when is the energy used in lattice vibrations, ii)when is it used in excitation of electron into higher energy level, and finally, iii)when is the energy utilized for slight vibration of the electron...

I have some basic doubts regarding how the energy is transferred (e.g. transmission of radio waves) as EM waves. As I know, the wave is not anything that can be practically seen in the space, but it is a model that we use to describe how energy is transferred. But if we think practically, how...

Does light exhibit any type of dispersion in a vacume?

My notes say that Heinrich Hertz was the first to generate and detect EM waves in the lab. ... Uhhh, this might seem really basic to you guys, but what exactly are EM waves? Because I thought they were any type of wave that appears on the electromagnetic spectrum, including visible light...

What exactly is tempertaure? As far as I know it represents the average vibration of atoms. How it relates to EM wave? because I have read in many Physics texts saying that 'the temperature of this wave is X Kelvin'. How do they find the temperature of individual EM wave? Correct me if I...

Will the frequency of EM waves produced by oscillating current in an LC circuit be the same as the frequency of the current? Thanks!

1. Since skin depth is the attenuation of the wave in a conductor, this means the reflection isen't the incident wave... so what is the reflection? 2. Water doesn't stop light since it's frequency is too high, i saw on forum it's because the big ions can't move fast enought. How can that be...

Hi all, I was reading "Geometrical Optics Reflected Fields" chapter from "Introduction to Uniform Geometrical Theory of Diffraction" textbook. The author assumed that the surface is perfectly conducting and therefore he only considered the reflected waves. He derived a formula for the...

Homework Statement Two incoherent EM waves of intensities 7I0 and 13I0 travel in the same direction in the same region of space. What is the intensity of EM radiation in this region? Homework Equations The Attempt at a Solution I have tried using I = I1 + I2 + ( 2* square root of...

We know that in electrodynamic when an incident Electromagnetic wave strikes a charged barrier it can either be reflected or transmits. And both of the incident, reflected and transmitted waves are in the same plane called plane of incidence. Now, i met a problem in which they state that the...

Are there any EM wave behaviors that cannot be explained in a purely physical, "photonic" manner? I'm speaking specifically of the photon's path from emitter to absorber, irrespective of "why" that path was taken (in other words, the double-slit experiment does not qualify in the context of my...

I am trying to review some basic physics, purely for my own interest, and have been looking at particle physics in the form of the Bohr model and EM theory in the form of Maxwell’s equation. While I still have a way to go on these topics, I was wondering if anybody is in a position to help me...

Show that the electric field: E = Emsin(kx-ωt) and magnetic field: B=Bmsin(kx-ωt) satisfy the following equations: -\frac{\partial B}{\partial x} = \mu_{0}\epsilon_{0}\frac{\partial E}{\partial t} and \frac{\partial E}{\partial x} = -\frac{\partial B}{\partial t} I have no idea...

I love Star trek and I was thinking, how to create a warp drive. I have read a discusion about EM waves on this forum, there was written that they do not need any medium for propagation and : “In a simplified sense the oscillating E field sustains the oscillating B field which sustains the...

Homework Statement Find the velocity of EM waves as a function of \epsilon_{0} and \mu_{0} 2. The attempt at a solution E = E_{0}cos(kx-\omega t) Using v= \frac{\omega}{k}

Homework Statement Sketch in 3D, the following waves. (both E fields are in x direction E_1 = 3*exp(-j*8*Pi*z) E_2 = 4j*exp(-j*8*Pi*z) (where j=sqrt(-1)The Attempt at a Solution I know how to sketch E_1, but my question is how to treat the imaginary amplitude, 4j in E_2. here is my stab at...

Ok my question is pretty simple and is in two parts. 1. say you created an em field what would have to an em wave the is propogating towards it. 2. what would would to an em wave if it went through an em coil. If you could would you be able to point me in the direction a...

Hi, Something has been bothering me about deriving the wave equation for a plane EM wave. We were showed this derivation in class and had to reproduce it but something is not making sense to me... The derivation is as follows: Suppose you have a plane EM wave (in a vaccuum) traveling in the...

Hi, i was wondering Sorry if i don't have the right words, i study in France Why are Microwaves better for heating up food ? I mean since E=hv, these should contain less energy Right now, i know vaguely, that atoms absorb photons where the energy can make it go from one of its characteristic...

Hi I was wondering how can antennas capture + receive Electromagnetic waves I was thinking, in particular of FM Transmitters Antennas, and Fm receiver Antennas. And also, how come metals act as a shield to EM Waves I know that antennas have a resistance, and that they consume Energy by...

Quote from Organic Chemistry, L.G. Wade, Jr.: "Not all molecular vibrations absorb IR radiation." "One of the component of an electromagnetic wave is E field. This field alternately stretches and compresses a polar bond." "If this alternate stretching compressing of the bond occurs at the...

can anyone help me derive the poynting vector from energy density of electromagnetic waves? and how we obtain average value <S> thanks

http://www.youtube.com/watch?v=5wnk6FVXCmc&feature=related That is one of several parts, 4 or 5 I believe. So is there any real science or truth to what he is saying? If he is correct it could quite possibly be the most important discovery in human history. Mind you, I'm not talking so...

Another thing that I've never really understood... As fas as I'm concerned, waves need a medium to travel through, but electromagnetic waves seem not to need one at all. I just can't visualise them as oscillations in anything. It sort of helps if I visualise EM waves as photons, because then...

This paper which just appeared on arxiv http://arxiv.org/abs/0709.2365 Loop quantum gravity corrections to gravitational wave dispersion Martin Bojowald, Golam Mortuza Hossain 27 pages (Submitted on 14 Sep 2007) "Cosmological tensor perturbations equations are derived for Hamiltonian cosmology...