How ac and dc generators work?

When a conductor moves in a magnetic field, an Electromotive Force (EMF) is generated in the conductor. This becomes an electric current through anything connected to the ends of the conductor. To generate a continuous current, a conductive coil (to multiply the EMF) is spun end over end in the magnetic field. As the coil moves in a circle through the straight field, the conductors have to change their direction, making the current change direction once every rotation (alternate). The alternating current is taken from the rotating coil by “slip rings” on the rotating shaft touched by stationary contacts. To undo the alternating, the moving ends of the conductor are exchanged every half revolution, at the moments in the cycle when the EMF passes through zero. This is done with a device called a commuator replacing the slip rings on the shaft that spins the coil: stationary contacts on opposite sides of the shaft touch two conductive half-cylinders attached to the ends of the conductor but insulated from each other. This will give a very “bumpy” direct current that can be smoothed by putting a condenser (capacitor) in the circuit.

(Edison was a great advocate of DC, but a transformer requires AC, so DC has to be used at the same voltage it is generated, a relatively low voltage that does not travel well. He envisaged a power station every city block! Edison is a greatly overrated man. His big invention was the research and development team, but he stole the credit for their inventions.)