It has been demonstrated that a voltage can be produced by rubbing a rubber rod with fur. Because of the friction involved, the rod acquires electrons from the fur, making it negative; the fur becomes positive due to the loss of electrons. These quantities of charge constitute a difference of potential between the rod and the fur. The electrons which make up this difference of potential are capable of doing work if a discharge is allowed to occur.
To be a practical source, the potential difference must not be allowed to dissipate, but must be maintained continuously. As one electron leaves the concentration of negative charge, another must be immediately provided to take its place or the charge will eventually diminish to the point where no further work can be accomplished.
A voltage SOURCE, therefore, is a device which is capable of supplying and maintaining a charge while some type of electrical apparatus is connected to its terminals. The internal action of the source is such that electrons are continuously removed from one ter-minal, keeping it positive, and simultaneously supplied to the second terminal which maintains a negative charge.
Presently, there are six known methods for producing a charge or electromotive force (emf). Some of these methods are more widely used than others, and some are used mostly for specific app-lications.
Following is a list of the six known methods of production of an electrical charge.
1. FRICTION - produced by rubbing certain materials together.
2. PRESSURE - (piezoelectricity) - produced by squeezing crystals of certain substances.
3. HEAT (thermoelectricity) - produced by heating the joint (junction) where two unlike metals are joined.
4. LIGHT (photoelectricity) - produced by light striking photosensitive (light sensitive)substances.
5. CHEMICAL ACTION - produced by chemical reaction in a battery cell.
6. MAGNETISM - produced in a conductor when the conductor moves through a magnetic field, or a magnetic field moves through the conductor in such a manner as to cut the magnetic lines of force of the field.
Follow along as I provide you with a tutorial on how voltage is produced utilizing each method mentioned above.