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We all know that light is an electro magnetic wave. but is electricity a EM wave? If it is then why light does not requires a medium to travel and why on the other side electricity needs a conductor ( I mean a medium) to travel. WHY? Or HOW?

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How is electric current an EM-Wave? A single electron traveling in empty space constitutes a current, but how is that a wave? It doesn't even radiate if not accelerated. –  nephente Feb 3 at 12:41
Well, for one thing, it doesn't. As an extreme example, look at electrons flowing from tip to surface in an arc welder. I think your confusion is that DC current involves moving electrons (or occasionally positive ions) around, while EM waves are an 'artifact' of AC field potentials. –  Carl Witthoft Feb 3 at 12:53
My book says, "the information about beginning of the flow of current is transmitted through the propagation of electromagnetic waves (electric impulse) and not with the drift velocity of electrons. Hence, the electric bulb turns on almost instantly, when the switch is closed." I think you meant something like this in saying electricity as EM wave. –  Godparticle Feb 4 at 11:08
@ VINAY you got me absolutely right. Please explain the same thing to these guys. –  Phantom Physicists Feb 4 at 12:56

3 Answers 3

up vote 1 down vote accepted

Electricity, understood as movement of electrical charges, can generate an EM-Wave, if the geometric conditions of the circuit and frequency conditions in the current flow are given.
As for the means to travel, it is interesting to refer to "skin effect." As the frequency of the current passing through a conductor is increased, the flow of electric charge moves to the outer surface of the conductor. When the wavelength of the frequency associated with the movement of electric charges, it becomes comparable to the conductor length, the phenomenon of "radiation" is produced.
Ultimately, the movement of electric charge is normally performed in a conductive medium. If the specified conditions are met, this movement can generate an electromagnetic wave, which can propagate even in a vacuum.
So, electricity is not an electromagnetic wave, but can generate a disturbance in the associated electromagnetic field that has the ability to spread like a wave.

Something interesting to note is that an electromagnetic wave can generate electricity (photoelectric effect).

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electricity is refered to the energy carried by electric current. EM are generated by accelerating charge particles e.g. in a dipole antenna when given an AC voltage input. The energy of current is transmitted as EM waves.
For sure electricity is not an EM wave rather EM waves can be generated through electricity.
I guess you got this doubt by considering lightning of clouds as electricity. The lightening you see is visible light produced due to the heavy de-exitation of a lot of atoms(molecules) of air.
Magnetic field is always prependicular to the current and is found in closed loops.

"Then why does light does not require a medium to travel".

The question of this kind always rises when we compare light waves with other kinds of mechanical waves say sound waves. And the answer can be Aether, if you mean by medium some physical thing , is the medium through which light travels. Alas ether is not founded yet.
What is Aether? Aether is really an "enfant terrible". Aether is a concept to explain light waves using the old machenical view of nature. Aether should be different from all other media's like air water etc. ,it should be of 0 density transmitting light waves at such a high speed. Nature has shown itself in such a way that all the attempts to use the old machenical view got failed.
Einstien's special theory of relativity poses an astonishing explaination of nature in which we do not need Aether to explain the motion of light.
The dual nature of light and matter gives the death to your question. you know electrons also behaves like waves , do electron waves need some medium to move through? If yes then at the same time they are particles too. A particle deosn't seem to need any medium to move.
Similarily light also shows dual character. Science has advanced so much that we now have accepted the modern view of nature because it describes the nature better than the old machenical veiw and gives more insight to the nature.

One can never tell why. One can only tell you how.
$1$ Art: The unsuccessful search for a medium for the propagation of light.(page 328) of book SPECIAL THEORY OF RELATIVITY by V. Α. UGAROV

$2$ Book: THE EVOLUTION OF PHYSICS by Albet einstien and leopold.
$3$ Art: Attempts to Preserve the Concept of a Preferred Ether Frame The Ether-Drag Hypothesis of book Introduction to Special Relativity by Robert resnik.
$4$ This article explained here

There are many more good articles about aether. Those i've mention are those which i'have read so i can promise you that these are good explainations to the best of my knowledge.

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"In several parts of this treatise an attempt has been made to explain electromagnetic phenomena by means of mechanical action transmitted from one body to another by means of a medium occupying the space between them. The undulatory theory of light also assumes the existence of a medium. We have now to shew that the properties of the electromagnetic medium are identical with those of the luminiferous medium." - Maxwell

Maxwell's displacement current is a physical displacement of the aether.

A light wave is an aether displacement wave.

Aether has mass, physically occupies three dimensional space and is physically displaced by the particles of matter which exist in it and move through it.

Displaced aether pushing back and exerting inward pressure toward matter is gravity.

The state of displacement of the aether is gravity.

A moving particle has an associated aether displacement wave. In a double slit experiment the particle travels through a single slit and the associated wave in the aether passes through both.

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