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E.M.Theory....

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I hav sum doubts about the fundamental concpts of E.M.Theory....As far as i knw an E.M. wave consists of an E field and a H field both of which vary wth time n distance....Why is it necesary for the fields to vary with time???Do the fields also vary wth distance???I mean is it necesary for them to vary wth distance as well????If yes,WHY???
 

BrownOut

Banned
They vary with time and distance. Otherwise, you have no wave. Go to the ocean and see some waves. That's how i do it.
 

crutschow

Well-Known Member
Most Helpful Member
You can have static E fields (from a charged surface) or H fields (from a permanent magnet). But that won't generate an E.M. wave. A wave, by definition, is oscillating, thus to generate an E.M. wave, the E and M fields must also oscillate (vary with time).

The fields vary with distance since the volume that the field occupies increases with distance from the source of the field. Think of how a light dims, the further you are from it.
 
Okkk....now wht happens when an E.M. wave encountrs a prfct conductr n a prfct insulatr????What is a prfct condctr n a prfct insulatr anyway???
 

JimB

Super Moderator
Most Helpful Member
Okkk....now wht happens when an E.M. wave encountrs a prfct conductr n a prfct insulatr????What is a prfct condctr n a prfct insulatr anyway???

I think you need a new keyboard.
A great number of the characters are missing.

JimB
 

omer_farooq_172

New Member
first of all the EM waves r produced when there is a chnge in either electric or magnetic field. The necessary thing is the word "change". if electric field changes it will produce a changing magnetic field and a changing magnetic field will produce a changing electric field.
this prcess continues by which the waves propogate.
simple example is of the mobile fone if recieves signals near any sound system there a sound is produced in the speakers.
this is also the effect of these fields if there comes a conductor in their path
further they pass directly through the insulators with no effect on either of the two
 

Sceadwian

Banned
Even super conductors aren't perfect conductors they only remove resistance from the equation. There is no such thing as a prefect insulator, neither can exist.
 
this is also the effect of these fields if there comes a conductor in their path
further they pass directly through the insulators with no effect on either of the two

I didnt quite get u...i believe a E field cannot exist in a conductor???What about an H field???
And wht happens to the E and H fields as they enter the insulator???Are the E and H fields inside n outside the insulator the same (in magnitude n phase)????
 

devronious2009

New Member
E and H fields permeate and could easily exist inside both an insulator and conductor. I think the answer your thinking of is electric current which is a different concept than an E and H field. E and H fields are forces, a current is a stream of charged particles which can create both. But in a conductor the transfer of electrons does not induce a net E field no. That's not to say you couldn't hook up electro static plates outside the conductor and permeate it with an electric field. Does that make sense?
 
Am pretty confused ovr here....all alng i knew that an E field cannot exist inside a conductor...it terminates on the surface n it is normal to the surface....could u xplain a bit more vividly...or refer 2 sum websyt for the same....
 

Sceadwian

Banned
I think it might be easier if you could reference where you were taught that an efield can't exist in a conductor. An electric field exists whenever there is a difference in the number of electrons between any two mutually influenced objects.
 

devronious2009

New Member
An electric field is a field that permeates and is permitted at the rate of one divided by the permittivity of free space. What would make you think it wouldn't pass thru the massive distance between atoms? That's in fact free space. The distance between atoms is quite large in relation to the size of the atom. There is a huge amount of free space area like outerspace in the atomic structure of a metal conductor. Is there something that would stop an electric field from permeating thru the conductor's free space?

Its like a gravity field, in fact they are very similar in falloff and geometry just one's more powerful then the other. But they're both fields that permeate.

Can the earths gravity be felt on the other side of the moon? Of course it can, likewise the electric field of a parallel plate dipolar device could easily permeate thru the atoms in a conductor and likewise be felt on the other side of the atoms within it.

Its just simple field mechanics. The evidence is the gravitational forces out in space. We have no reason to beleive that the field from an electric force does not behave similar tot he field of a gravitational force. Do we?

But if you would like to conduct an experiment, put one pole of an electric plate on one side of a conductor and the other pole plate on the other side and see if they attract each other, if they do then they definately permeate thru the conductor from the source of the field which is the plates.

In similar character, and this is something you can do quite easily, take two magnets and put them on each side of a conductor and see if they attract. its a field just like the electric and gravitational fields. An aluminum plate will do perfect for the conductor.

I think you are refering to the electric field created by electron chaining from an electromotive force, which is entirely different mechanics.

The fields don't just exist everywhere, they are radiated from a source. And if they are radiated and have an origin where the source is, then passing thru something and reaching the other side means that it is in fact passing thru and exists on the inside as well.

How do you think permanant magnets are made? The magnetic field is permeated thru a conductor which is heated and the atoms are affected and align with the magnetic field which is then cooled and they retain their alignment.
 
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Sceadwian,
when a E field is applied to a conductor the elctrons move opposite to the applied field and create an E field which opposes the actual E field....In fact the E field is created just to cancel out the original E field....So there is no E field INSIDE the body of the conductor....Where did i go wrong???

devronious2009,
the E field does exist on the other side of the conductor....It induces opposite polarity charge on the 2 ends (considering a rectangular metal slab for convinience) which act as source and sink......But the E field INSIDE the slab is 0....Thats what i meant....Please do correct me if am wrng....

I hav searched the net a bit....it has been mentioned in quite a few cases that the E field inside a conductor is 0 only for static E fields....may b thts where the problem lies...could u elaborate on that please???
 
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