Electromagnetic

Electromagnetism is the fundamental force called electromagnetic force. We look to the diagram above for a simple explanation.

The image above represents a sliced view of a coil, so we’re looking at it as if it’s been cut in half. The Xs and the DOTs in the image represent the flow of electricity in the coil, the dots are where the electricity is coming out of the page, and the Xs represent the electricity going into the page. This representation is commonly understood as the right hand rule, which in this case, you use the fingers of your right hand to wrap around in the direction of the electricity. If you then point your thumb straight out, you’ll see the direction of the electromagnetic forces, which is represented here with the lines and arrows on them.

source: http://www.oocities.org/rjwarren_stm/Physics_Notes/U4_Electro.html

The electromagnetic force is always present when there is current, ie. the flow of electrons.

In 1873, James Clerk Maxwell published his Treatise on Electricity and Magnetism, where he states specifically four observations:

1. Electric charges attract or repel one another with a force inversely proportional to the square of the distance between them: unlike charges attract, like ones repel.
2. Magnetic poles (or states of polarization at individual points) attract or repel one another in a similar way and always come in pairs: every north pole is yoked to a south pole.
3. An electric current in a wire creates a circular magnetic field around the wire, its direction (clockwise or counter-clockwise) depending on that of the current. (right hand rule)
4. A current is induced in a loop of wire when it is moved towards or away from a magnetic field, or a magnet is moved towards or away from it, the direction of current depending on that of the movement.

If we pay specific attention to his observation four, we can now see the fundamental knowledge that allows the electric generator to work.

source: http://www.gcsescience.com/pme18.htm