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Electric Current
Electrons, while they can flow, do not flow through all materials equally and in some materials not at all. When electron can move through a material it is said to be a conductor and when a material inhibit the flow of electron it is said to be an insulator. For example copper and most metals are good conductors and rubber, glass, plastic and wood are good insulators. When electron do flow, it is called a current. And since the always try to maintain a balance electron always flow from a high concentration to a low concentration.
As electron flow through a wire they create a magnetic field. A major part of the the modern world relies on this effect. It drives motors and has numerous other applications. The magnetic field runs round the wire in a anti-clockwise direction (when looking down the wire from negative to positive). If you place a thick wire along the north, south of the compass with north positive and south negative. Once you connect it to a current you will see the needle swing clockwise to face east west.
The first basic use of this magnetic field is a way to measure current. Moving the needle of the compass against a spring gets us a analog current meter. If a small amount of current moves through it moves the needle a small way, not having enough power behind it to push against the spring. If there is a large amount of current the magnetic field is stronger and will push harder against spring. So the further the needle moves the stronger the current. Modern analog meter use a coil of wire to build up the magnetic field and provide a greater sensitivity.
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