Electricity is produced in different ways from different sources. The most common sources are friction (static), heat (thermocouple), light (photo cell or solar cell), pressure (crystals), magnetism (generators) and chemical action (battery).
1. Static electricity is produced by friction. In friction, electrons in an insulator can be separated by rubbing to produce opposite charges that remain in the dielectric.
2. Heat energy is converted into electrical energy through the use of a device called thermocouple. It is a device consisting of two dissimilar metal wires twisted together at one end but open at the opposite end. When the joined end is heated, it produces a low DC voltage at the open end. The voltage produced by this device is directly proportional to the temperature of the metal wires. To produce a higher voltage, a number of thermocouples may be joined together.
3. Photoelectric matter. Some materials are photoelectric, which means that they can emit electrons when light strikes the surface.
A device called photovoltaic cell or photo cell is made of a vacuum tube with two electrodes. One electrode is coated with sensitive materials such as cesium or selenium which give off electrons when illuminated. These electrons strike the other electrode which in turn, collects the electrons. If the tube is combined with a fixed voltage source, there will be electron flow in the circuit and this will activate photoelectric devices such as television cameral tubes, phototransistors, alarm systems and photoelectric cells.
4. Pressure (crystals). Certain crystals such as quartz crystal is applied to produce the voltage needed to establish operating frequencies for radio and TV sets.
5. Magnetism. Any moving charge has an associated magnetic field and any changing magnetic field can produce current. A motor is an example of how current reacts to a magnetic field to produce motion. If the rotary motion results from the conversion of electrical energy into mechanical energy, the process can be reversed to change mechanical energy into electrical energy. This is done by using an electric generator, which produces voltage by means of a conductor rotating in a magnetic field.
When large quantities of electric power are needed, electric generators in big power plants get their mechanical energy from the following:
A. water or hydroelectric power
B. steam/turbine power (includes fossil, carbon, nuclear, and geothermal powers;)
C. engine power (which makes use of diesel or gasoline); and
D. wind power from windmills.
6. Batteries. A battery is made up of several individual cells wired together to produce a bigger amount of energy. Batteries are categorized into wet and dry cells.