In the early 19th century the following similarity between two charged particles and two magnets was observed:

• both created "forces" that could operate in a vacuum

• charge had a postive and negative component; magnets had a north and south pole force could then be either attractive or repulsive.
  

• both the magnetic force and the electrostatic force strength decreased as 1/R²

In 1820 Oersted did this experiment:

and discovered that an electric current creates a magnetic field

Similarly, a coil of wire with a current passing through it generates a magnetic field. This is known as an electromagnet or solenoid .

So now we know that a current can create a magnetic field. If a magnetic field can create a current then we have a means of generating electricity. Experiments showed that a magnetic just sitting next to a wire produced no current flow through that wire. However, if the magnet is moving a current is induced in the wire. The faster the magnet moves, the greater the induced current.

This is the principal behind simple electric generators in which a wire loop is rotated between to stationary magnetics. This produces a continuously varying voltage which in turn produces an alternating current .

Visualization of a simple electric generator:

To generate electricty then, all we really want to do is have some (mechanical) mechanism turn a crank that rotates a loop of wire between stationary magnets. The faster we can get this crank turned, the more current we can generate.

Popular Methods of Turning the Crank:

• Let water fall on it (Hydro Power)
• Direct a nozzle of steam at it (Coal, Nuclear Fired Steam Plant)
• Let the wind turn it (windmill)
• let the sun make steam: