Electrical principles - Creating electricity

Sources

There are six sources of electromotive force (voltage)

• pressure
• magnetism
• heat
• light
• chemical
• friction.
  

Chemical

A battery uses a chemical effect to produce electromotive force: The chemical effect is achieved by placing two dissimilar metals into an electrolyte. An example is the placement of a copper and zinc electrode together in a solution of sulphuric acid. As the two metals react, they create a voltage potential.

When a battery cell is connected to an external source, its chemical energy will decrease as the cell produces electrical energy. When the chemical energy of a dry cell battery has expired it will no longer deliver electrical energy. This makes it a temporary voltage source.

Light

The sun's rays can be used to produce a voltage potential. This is achieved using a solar cell (commonly called a photoelectric (pe) cell). The solar cell is a thin junction made of two different types of semiconductor materials. Light falling onto these semiconductors causes electrons to move freely, creating a potential difference. The most common types of semiconductor used are silicon, boron and phosphorus. Solar cells are often used for battery charging in remote areas as well as powering street lights and road signals.

Heat

A voltage is created when two dissimilar metals are joined together and one end of the metal is at a different temperature to the other. This will create millivolts only, but by connecting a number together in series or parallel an increased voltage can be obtained to use with electronic circuitry. A common use of this technology is in a thermocoupler. Thermocouplers can be used to measure and control temperature.

Pressure

When a quartz crystal is cut and subjected to stress it creates a difference of potential across the material. This is called the piezo effect. The most common uses are in electronic scales or gas igniters on stoves.

Magnetism

The most common way of creating an electromotive force is by using magnetism. When a conductor passes through a magnetic field, cutting through the invisible lines of flux, a voltage is induced into the conductor.

This method of creating electromotive force is used in:

• wind generators
• tidal generation
• hydro plants.