Electrical energy can be obtained from heat. If a copper and an iron wire are joined to form a complete circuit and heat is applied to one of the joints, an electrical current will be set up in the circuit. The current, however, will be very small so that electricity from heat is not commercially practical. The principle does have a practical use for electrical measuring of radio currents, such as the thermo-ammeter (the heat ammeter) in which a very small current produced by heating two different metals is sent through an ordinary meter.
ELECTRICITY BY CHEMICAL ACTION
Batteries used for converting chemical energy into electrical energy are far more important than most people realize. Because of the great publicity given to A.C. Radio sets in recent years, many people have the idea that batteries are out of date, that they belong to a past age, and that
Fig. 4
one can be an Expert Radio-Trician without knowing anything about the conversion of chemical energy into electrical energy.
You probably might know that this is far from being true. Aircraft Radio, Marine Radio, Broadcasting Radio, Television Transmitters and Receivers, Public Address Systems, etc., depend to a certain extent on battery power. Besides, batteries furnish power for the automobile and pleasure boat radio which is becoming more popular all the time. Batteries are frequently used in sound picture studios and in the projection booth. Thousands of homes in some towns, rural communities and on farms not wired for A.C. or D.C. depend on batteries.
Batteries will always be used in the laboratory and at the Radio-Trician’s work bench.
Batteries generate e.m.f. that is continuous and unchanging in strength.
