Electric Current Generation

Let us reconsider a few of the many methods available for generating electric currents. There are at least four principal ones: 1. chemical reaction; 2. thermal or heat action; 3. light action, and last but not least, 4. magnetic action.

In a battery currents produce chemical effects and the process is reversible. In other words, batteries can generate electricity by moans of chemical reactions. To produce a current by chemical reaction, an alkali or an acid is made to react with a metal. The device to be used is called a voltaic or an electric cell, a group of two or more cells connected together forming a battery. The reader is certain to remember that the voltaic cell is so named after Volta, its inventor, who was the first to show that electricity could be generated owing to chemical reactions.

Producing current by thermal action is the next method to be considered. Heat is certain to produce current when applied to two unlike metals soldered together in two points. The apparatus used is called a thermoelectric couple or thermocouple, for short. The word "couple" used in this term should mean that two unlike metals or metals and alloys, say, such as cooper and constantan arc joined together so that they can be properly heated in the point of the joint.

The reason the thermocouple generates current is due to the fact that the heat tears the electrons off of the negatively charged metal at the point of joint, just as the electric cell chemical reaction is expected to tear the electrons off of the zinc electrode. It is these electrons that constitute the current flowing through the circuit.

Our physicists are known to have produced semiconductor thermo elements, which without any machinery convert thermal energy into electric energy as efficiently as small steam installations do.

Falling on a special kind of cell, a light beam can generate an electric current. The appliance using that phenomenon to produce electricity is called a photoelectric cell. Photoelectric cells appear to be used in a great number of common devices. One can't help mentioning lasers, too, since it has been found that laser powerful beams can be turned into electricity with a very high efficiency.

To generate a current by magnetic action, a wire is made to pass through a magnetic field, the latter being set up either by a permanent magnet or an electromagnet. In the case of the wire cutting through the magnetic field of a permanent magnet, the appliance is called a magneto-electric machine or simply "magneto". The wire cutting through the magnetic field of an electromagnet, the apparatus is said to be a dynamo electric machine or a dynamo, for short. Generally speaking, there are several ways by means of which electric currents can be generated by magnetic action, all of them being based on the same principle, namely, on cutting magnetic force lines with a conductor.

You are likely to think that the dynamo is similar to an electric motor. In principle you are right. Any d. c. motor may be used as a generator simply by rotating the armature. Nevertheless, the construction of both types of machines differing in details, a machine designed as a motor does not make a very efficient generator.