Difference between revisions of "Electromagnetism"
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| − | '''Electromagnetism''' | + | '''Electromagnetism''' is the branch of [[physics]] which studies electric and magnetic phenomena. Electric and magnetic effects were known and even used by ancient civilizations, for example the Chinese used the compass, which is based in the magnetic field of the Earth at least from the year 1000 BC. However, a comprehensive theory of electricity and magnetism, which turned out to be different aspects of the same thing, had to wait until the XIX century with the works of [[Michael Faraday]] and [[James Maxwell]]. Einstein theory of relativity brought new insights to electromagnetic theory. |
| − | A | + | An electric charge A produces an [[electric field]] around it. The electric field is a somewhat abstract entity, it can be better understood as something that a second charge B “feels” when placed on it. So, when charge B is placed in the electric field generated by A, it will feel a force directed towards or away A. The force is attractive if both forces are of the same sign, and repulsive if they are of opposite sign. In any case, the electric field, and thus the force felt by B, is in a radial direction around A. (A is in the centre, and the field looks like rays coming out of it). |
| − | + | A continuous flux of electric charge is called an electric current. An electric current (indeed any moving electric charge), produces a [[magnetic field]] around it. Again, a magnetic field is an abstract concept; it can be intuitively understood as something that is felt by a compass. So, if a compass is placed near an electric current, its needle with point approximately in the direction of the magnetic field produced by the current (If it is strong enough so that the Earth magnetic field can be neglected). The direction of the magnetic field is at ninety degrees with respect to the direction of motion of the charge or current. For example, in the case of a straight conducting wire, the magnetic field produced circles around the wire. | |
| + | |||
| + | The classical theory of electrodynamics is completed with three more fundamental principles: | ||
| + | The first is that there are not isolated magnetic charges, also called magnetic monopoles. All magnets must have a north and a south pole. A magnetic monopole would be the magnetic equivalent of an electric charge. | ||
| + | The other two principles are that a changing electric field produces a magnetic field, while a changing magnetic fields produces an electric field. | ||
| + | |||
| + | All classical theory of electrodynamics can be mathematically expressed in a set of four equations called the [[Maxwell's Equations]]. | ||
==See Also== | ==See Also== | ||
* [[Electricity]] | * [[Electricity]] | ||
| + | * [[Magnetism]] | ||
[[Category:Physics]] | [[Category:Physics]] | ||
Revision as of 00:32, July 5, 2009
Electromagnetism is the branch of physics which studies electric and magnetic phenomena. Electric and magnetic effects were known and even used by ancient civilizations, for example the Chinese used the compass, which is based in the magnetic field of the Earth at least from the year 1000 BC. However, a comprehensive theory of electricity and magnetism, which turned out to be different aspects of the same thing, had to wait until the XIX century with the works of Michael Faraday and James Maxwell. Einstein theory of relativity brought new insights to electromagnetic theory.
An electric charge A produces an electric field around it. The electric field is a somewhat abstract entity, it can be better understood as something that a second charge B “feels” when placed on it. So, when charge B is placed in the electric field generated by A, it will feel a force directed towards or away A. The force is attractive if both forces are of the same sign, and repulsive if they are of opposite sign. In any case, the electric field, and thus the force felt by B, is in a radial direction around A. (A is in the centre, and the field looks like rays coming out of it).
A continuous flux of electric charge is called an electric current. An electric current (indeed any moving electric charge), produces a magnetic field around it. Again, a magnetic field is an abstract concept; it can be intuitively understood as something that is felt by a compass. So, if a compass is placed near an electric current, its needle with point approximately in the direction of the magnetic field produced by the current (If it is strong enough so that the Earth magnetic field can be neglected). The direction of the magnetic field is at ninety degrees with respect to the direction of motion of the charge or current. For example, in the case of a straight conducting wire, the magnetic field produced circles around the wire.
The classical theory of electrodynamics is completed with three more fundamental principles: The first is that there are not isolated magnetic charges, also called magnetic monopoles. All magnets must have a north and a south pole. A magnetic monopole would be the magnetic equivalent of an electric charge. The other two principles are that a changing electric field produces a magnetic field, while a changing magnetic fields produces an electric field.
All classical theory of electrodynamics can be mathematically expressed in a set of four equations called the Maxwell's Equations.
