what does one mean by "time varying" electric fields?
156038
That means they change wih time. I do not understand your question. \n\nSuppose I measure the electric field at some location, X=10. If I move a charge close to X=10, say to X=9, then away to X=1, then back to X=10, then the electric field varies with time as I move the charge closer and then farther. It is a time varying electric field.
31993
Where ever an electic charge is made to oscillate there will be electic field and magnetic field.\n\nNowadays every one is familiar with cell phones.The cell phones receive the electric and magnetic field produced at the transmitting end.\n\nRadio ,T.V are other examples of receiving electic and magnetic fields.Very very familiar example is the light which we see.\n\n Light is one form of electic and magnetic field. Hence whenever we open our eyes we feel the precence of electic and magnetic field.\n\nAs a crude answer  when ever we see we find electric and magnetic field.
864979
The speed of the propagation of the electric field within a wire is limited by the speed of light.  Information cannot travel faster than light, so if you switched on a light bulb millions of miles away it would take a very noticeable lag before you see the light come on.\nFirst the electricity must travel down the wire at a speed no faster than c, then the light emitted by the bulb must return at c.\n\nIt is important to note that although the influence of the electric field propagates at the speed of light, the electrons making up the electric current do not travel this fast themselves since they have mass.  The individual electrons in the current carrying wire travel much more slowly.  The electrons that go "into" one end of the wire are not the same electrons that "come out" of the other end.
220810
No equations but this may help.... when an electrical signal is travelling along, for example a piece of copper wire, there will be a field generated aroung the cable, similar to that of a magnet (remember at school we were taught about magnetic fields  with a magnet piece of paper and iron filings)\nWhen a second piece of wire is brought in close proximity to the 1st piece then it will cut the field , and a signal will be induced into the second piece of wire.This is called mutual induction. If a signal is now added to the second wire then the induced signal will either add or detract from it dependant on the phase at the time.... this will happen, also within the 1st piece of wire, as a field is now being generated by a signal supplied to the second wire.\nNow, by twisting the pairs together the field generated by the signal in the wire will be changing direction along its length (positive then negative then positive and so on)thus cancelling any induced signals (could be crosstalk in a speach circuit) out
86731
The splitting and shift of a spectral line into several components in the presence of an electric field.
243034
magnetic fields, if moved in the right way, can create electric currents. Those currents could mess with the nucleus and take it from metastable to unstable. All depends on how the magnetic fields are set up and how you change them.
319281
Faraday's Law: Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. No matter how the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.
1076485
i dont know much about physics but i did a search and this is what i got hope it has what you're looking for:\n\nhttp://science.electronicsinfoline.com/Physics/Electricity_and_Magnetism/
565906
Electromagnetic radiation travels (propagates) by means of oscillating electromagnetic fields that pass through the air and the vacuum of space equally well, and does not require a medium of transport (such as the aether). When radio waves pass an electrical conductor, the oscillating electric or magnetic field (depending on the shape of the conductor) induces an alternating current and voltage in the conductor. This can be transformed into audio or other signals that carry information. The word 'radio' is used to describe this phenomenon, and television, radio, radar, and cell phone transmissions are all classed as radio frequency emissions.
363705
An electric field due to stationary positive or negative electric charges starts to look a bit like a magnetic field due to north and south magnetic poles when you move through it faster and faster.   If you could reach the speed of light it would look exactly like a magnetic field, and conversely a magnetic field looks more and more like an electric field the faster you move.   The reason physicists lump these two phenomena together is that they're two aspects of the same thing, and what they both look like depends on how fast you're moving through the electric or magnetic field.   So the answer to your question is yes, there's a difference, and yes, electricity always involves magnetism.   An electromagnetic wave, like light, consists of an oscillating electric field which produces an oscillating magnetic field which produces an oscillating electric field which...
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Electric current is the flow of electric charge. This can be electrons or charged ions, like in electrolyte solutions. \n\nElectrons are the charge carriers in metals. They follow an an erratic path, randomly bouncing from atom to atom, but generally drifting in the direction of the electric field.\n\nThe net drift speed of the electrons is therefore slow, of the order of mm/sec in copper wires.\n\nHowever, electric current signals are waves which propagate at very high speed, close to the speed of light in the medium.
212659
Electromagnetic fields. In the classical view, a charged particle experiences a magnetic force when it is at some non-zero velocity with respect to a magnetic field. This is in addition to any electric force from any electric field that is present.\nRelativity theory unites these two fields as it reveals that a magnetic field is just what an electric field "looks like" to a charged particle when there are non-zero relative velocities involved.\nQuantum field theory (specifically quantum electrodynamics aka QED) further simplifies this by viewing electromagnetic force interactions as exchanges of "virtual photons".\nAs was said before, depending on the scale of the system, any of the other 3 fundamental forces may non-negligibly affect the particle as well.
473172
You've actually got several concepts and questions merged together.\n\nWhen you ask "how does the aerial setup the waves from only the ac signal?"  I assume you're asking how any DC components of the signal get filtered out?\n\nA transverse electromagnetic wave involves both a VARYING electric field and a VARYING magnetic field, appearing at right angles to each other and to the direction of travel of the wave.\n\nAny DC component has no varying component, therefore, no wave is generated.  Although DC flowing through a wire creates electric and magnetic fields, no wave is generated because there is no variance in the fields.  \n\nThere are other electronics concepts that require the changing electromagnetic fields of AC to work.  A transformer uses AC, not DC.  A capacitor will block DC signals, but allow AC signals to pass.\n\nAlso, as you indicated, an efficient antenna has a matched impedance to the signal source in order to maximize the amount of engergy propagated by the antenna in the desired direction(s).
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Electrostatics is the study of static or non time varying electric fields.\n\nElectromagnetics is the more general term applied to the study of electric and magnetic force fields.  Usually most situations deal with time varying currents producing time varying magnetic fields.  Maxwell's equations show us that time varying magnetic fields produce time varying electric fields.\n\nThe rest of electromagnetics is the study of the physical properties of these force fields, how they behave in a conductor, how antennas can radiate these fields, etc.
428861
to move back and forth from the frequency to the time domain
276990
read this page\nhttp://en.wikipedia.org/wiki/Field_(physics)
504604
Time constants in electronic circuits.