Homework Statement Suppose that a police car on the highway is moving to the right at 28 m/s, while a speeder is coming up from almost directly behind at a speed of 34 m/s, both speeds being with respect to the ground. The police officer aims a radar gun at the speeder. Assume that the...
Hello,
I took an Electrodynamics course this semester, where we derived Maxwell's equations from the field's Lagrangian density.
As a motivation, we "looked" for a scalar (in the relativistic sense) having something to do with EM fields - and had we found one we would have declared it a...
I understand that E^2 - B^2 is invariant under various transformations.
If we consider the vector ( E, B ) as a column, then E^2 - B^2 is preserved after mutiplication by a matrix -
| cosh( v) i.sinh(v) |
| i.sinh(v) cosh(v) |
I think this transformation belongs to a group...
Maybe the wrong word but can you get electromagnetic radiation in any frequency or is there a "quantum" frequency for which all other frequencies are some integer multiple?
Related question - is there an absolute low and high frequency?
I understand that the quantities
E^2 - B^2
\vec{E} \cdot \vec{B}
(the dot is vector inner product).
where E and B are the electric and magnetic components of an EM wave,
are invariant under Lorentz/Poincare transformations.
Can someone explain the physical significance of this ? Is...
Homework Statement
For a time independant or static situation
-\int_{a}^{b} \vec{E} \bullet d\vec{l} = \Phi(b) - \Phi(a)
a) Show that for any closed path
\oint \vec{E} \bullet d\vec{l} = 0
b)Using Stokes Theorem show that
\oint \vec{E} \bullet d\vec{l} = 0 implies \vec{\nabla}...
Why does the Lagrangian density for the EM field in a dielectric medium take the form d^3 \bf x \left[ \epsilon \bf E^2 - \bf B^2 \right]? I can see that the expression for Lagrangian density has units of energy per unit volume as you would expect but that's about it. Much appreciated.
Show that the action integral for the electromagnetic field in a matter with dielectric constant \epsilon is given by S_m=\frac{1}{8 \pi} \int dt d^3 \bf x \left[ \epsilon \bf E^2 - \bf B^2 \right]
where the standard expressions for the E field and B field E=-\frac{1}{c}\partial_t \bf A -...
How an em wave propogates??
i understand that an em wave can be produced due to an oscillating electric field or oscillating magnetic field... but how does this wave move forward at the speed of light??
This should be possible with table top experiments rather than LHC scale experiments:abstract:
Electromagnetic radiation decays with 1/r in three dimensional
space, while the non radiating Coulomb field decays faster with 1/r^2.
The general expressions for any dimension are 1/r^{(d-1)/2} for...
I have a question about the EM Spectrum. Is it existing in strips or is it completely continuos? Can a photon have a frequency of any value or does it have to have specific wavelengths according to the space between 2 electron orbits? I understand photons are generated when an electron drops...
So I have an upcoming project that I started working on. I thought I had the foundation to actually tackle the task at hand, but now that I've started it, I realized I'm kind of weak with some fundementals. If someone would be so kind to read what I am going to type, and add to it, or tell me...
Instead of calculating relative mass and density of an object to quantify gravity and gravitational forces, could Em field density be inserted into these calcs? why the shift from EM to Gr, relative to size? I know string theory is all the rage for unification, but why complicate an already...
Yup another "oh crap I don't have the book" issue. EM Fields, Wangsness
my elements of solid state physics book finally came in the mail but now I need my EM book
If you have it I just need the questions, the book got returned to sender so I need to wait longer for it than expected(I'm not...
I'm doing some calculations and I've run into something rather strange.
I need to evaluate the following dot products
\vec{\epsilon}_{k,\,s}\cdot\vec{\epsilon}_{-k,\,s'} = ?
\vec{\epsilon}_{k,\,s}^*\cdot\vec{\epsilon}_{-k,\,s'}^* = ?
where \vec\epsilon_{k,\,s} is the normalized...
when you integrate the energy density (from electromagnetic field) times the differiential volume of the whole 3D space for a photon...would you get the energy of it? E=hf ?
one more question... if there is a positive charge in 3d space... when i integrate the electromagnetic energy density...
Hi, I have a question about electromagnetic amplitudes. we can easily find the wavelength of any EM, but how do we determine its amplitude? in terms of joules vs. length vs. frequency?
I was wondering if there is upper and lower limit (absolute) of frequencies for electromagnetic waves?
My reasoning was as follows: the lower limit is bound by close to 0 Kelvin temperature of emitter and the upper limit of possible frequency for EM wave is by "planck's time" by relationship...
I question the educational value of such an exam. We've been working out of Jackson this year, and based upon my experience the typical jackson problem (just one) takes at least two hours, even if you know what you're doing and make minimal mistakes (ie dropping signs, forgetting terms in your...
What is the factor that determines whether an object will be transparent, translucent, or opaque?
Also, what makes reflecting surfaces reflect EM rays?
I'm attempting to calculate the above, but I'm stuck.
What I have thus far:
intensity is the time average of the poynting vector, where the poynting vector is the cross product of the E and B fields.
Using the given expressions, I get:
\frac{\sqrt{a^2 + b^2}}{\mu \omega} E_0^2 \exp(-2bz)...
Hello,
Here on this movie:
http://video.google.com/videoplay?docid=2256433507046558974&q=tesla&pl=true
at 19:35
There is shown Tesla's engine, which balances EM forces, that are able to raise a piece of metal into the air which then keeps on staying there.
If anybody is familiar...
I was debating on another forum about EM Pulse (yes, I just watched War of the World :-p ).
Anyway, does anyone know exactly what electrical components will be damaged by an EMP?
I know silicon chips would be dead, but what about capactors, diodes, resistors, etc.
Also, if a cars...
An electron is initially at rest. At a time t1 = 0 it is accerated upward with an acceleration of 10^18 m/s^2 for a very short time (this large acceleration is possible because the electron has a very small mass). We make observations at a point A, which is 15 meters to the right of the...
Can a monochromatic plane EM wave exists in a plasma when \omega is less than \omega_p (the plasma frequency)? If so, is it attenuated?
I read in a text that a wave incident on a plasma with \omega < \omega_p is completely reflected, but does this mean such a wave can't exist in a plasma?
If...
Here is the question i am working on:
An AM radio station broadcasts with average power 4000 W in all directions. A dipole receiving antenna 65 cm long is at a location 4 miles from the transmitter. Compute the amplitude of the emp that is induced be this signal between the ends of the...
Hi, if someone could help me figure this out I'd really appreciate it.
Estimate the average power output of the Sun, given that about 1350 W/m^2 reaches the upper atmosphere of the Earth.
I know the answer is 3.8 X 10^26 W but I don't know how to get there. I've tried different equations...
I'm a little confused about what happens when we connect two objects by a wire. Does this just equal the potentials, or does it equal the charges? Also, does this depend on the nature of the objects (is it different for e.g conductors or capacitors?)
thanks for your help
I thought in classical physics, only four forces account for all mechanics:
1 gravitational attraction
2 electromagnetic force
3 nuclear strong force
4 nuclear weak force
There is also a Lorentz force on a charged particle moving through a magnetic field. How does classical EM...
A circular parallel plate capacitor has plates of radius 0.1m; the plates are separated by 0.10 mm. A current is supplied to charge the capacitor. While charging, the potential difference across the capacitor increases by 10 V/μs.
What is the magnitude of the rate of change of the electric...
Hello,
I need to purchase two books, for EM theory and Thermodynamics. I have briefly used couple of books years back and I can't seem to remember their titles or author. I slightly remember that the EM book was a blue color with a lots of information for first year - 4th year...
Whats the simplest proof that the Electromagnetic laws are independent of frame of reference? .What I know is contradiction method which einstein also used to conclude the postulate of SR.
BJ
I have a little doubt.
EM waves are coupled electric and magentic oscillations. But, to produce an electric field you need a charge and for a magnetic field, you need a moving charge ,but,electric field doesnot exist with a moving charge. So, what is the source of Em waves and moreover how...
Suppose I have an eliptically polarizied EM wave, whose electric field can be written as
\vec{E}=A\cos(kz-\omega t)\vec{e}_x+B\sin(kz-\omega t)\vec{e}_y,
where the constants A and B are amplitudes of the x and y components of the beam, respectively.
How would I report the amplitude of the...
I'm not sure if this belongs here or in the relativity forum but associated with an electromagnetic wave is a magnetic field B and the force of this field on a charge q with velocity v is qv x B. Since any charge will be moving with speed c relative to the wave, will the magnetic force on a...
I've read in a book, that if you had a standing electromagnetic wave between two metal plates, only nodes would be at the metal plates. This is due to the infinite high conduction of metal, the book says.
Why is that so?
argh hello guys, I've been trying to find out a simple answer to this question but all the resources I've looked at seem to skim over it or contradict each other, but simply:
Do electromagnetic waves have a variable amplitude? "Intensity" is not necisarilly the same, if you're using the...
I'm unsure what I'm doing wrong here... it has to be something. So let me explain the problem:
I'm supposed to rank the net magnetfic field strength for various arrangements. In all of the arrangements the magnitude of the current is the same. The distance between each of the charges is the...
http://www.surrey.ac.uk/qe/pdfs/cemi_theory_paper.pdf
I approached this initially with extreme skepticism, especially since it seemed impossible considering the myriad em fields we're immersed in without any perceptible effect on our consciousness, but I ultimately walked away viewing this...
Choosing the Lorenz gauge implies that sources of the EM potentials at a given point are the charge density (for scalar potential) and current density (for vector potential) that cross a collecting sphere converging at the speed of light toward that point. It is often said that the retarded...
This paper (broken into three peaces; see attachments below) introduces a re-discussion of the Lagrange density. The tool to get this result is a new mathematical operation whose existence can be guessed from some considerations concerning the calculation of the variations along the time of the...
Hi,
My question:
Explain how an electromagnetic wave is produced?
My Answer
A charged particle produces an electric field. the electric field exerts a force charged particles. Positive charges accelerate in the direction of the field and negative charges accelerate in the direction...
just want to ask what are electromagnetic waves and how are they produced?
also, do you where i can get a simple application of EM waves? just really need it... thanks!
This isn't really a brain teaser as much as a game.
I have a Five Crowns deck at home. This consists of a deck of 55 cards (well, two decks of cards) with five suits. 3 is lowest and King is highest. You can't do 3-King in a straight.
There are jokers, but I'm not using them --...
I have a photointerrupter sensor that is near an electric motor in a scooter and I'm tyring to tap into it. When I tapped into the sensor with a wire, the scooter stops running. Initially I thought it was my speedo circuit but then i found out that if I tap into the sensor with just a plain...
Consider the following general Hamiltonian for the electromagnetic field:
H = \int dx^3 \frac{1}{2} E_i E_i + \frac{1}{4}F_{ij}F_{ij} + E_i \partial_i A_0 + \lambda E_0
where \lambda is a free parameter and E_0 is the canonical momentum associated to A_0, which defines a constraint (E_0 =...
ok i have been thinking about this problem for a lil bit now and i think i have it correct but i would just like to double check:
(a) twelve equal charges, q, are situated at the corners of a regular 12-sided polygon (for instance, one on each numeral of a clock face). What is the net force...
Hello:
I will try to meet the terms of the 8 guidelines.
1. The behavior of light is explained with a rank 1 field theory, the
Maxwell equations. Gravity is explained with a rank 2 field theory,
general relativity. The two can be combined in one Lagrange density,
but they are not in...