ELECTROMOTIVE FORCE. GENERATOR

№ 19. ELECTROMOTIVE FORCE

The driving force tending to produce the motion of electrons through a circuit is called an electromotive force, or e.m.f. for short. It is the e.m.f. that moves electrical charges from one point in the circuit to another. The greater the electromotive force, the greater the pressure on the electrons moving through the conductor. The e.m.f. is measurable and the volt is the unit in which it is measured. The unit of the e.m.f. is the electromotive force of such a source of energy whose work on carrying one coulomb equals one joule. One should distinguish between an electromotive force and potential difference. A generator or a battery is a source of the e.m.f. whereas the voltage across a resistance in which a current is flowing is a potential difference.

There are four devices for supplying electrical energy to a circuit, namely: 1. The cell which transforms chemical energy into electrical energy. 2. The dynamo-electric machine which transforms heat into electrical energy. 3. The thermocouple which transforms heat into electrical energy. 4. The photo-element which transforms light energy into electrical energy.

№ 20. GENERATOR

The purpose of the generator is to provide current for lighting and ignition. It keeps the storage battery in properly charged condition. The rotating part is the armature. This is fixed on a shaft. The armature windings are connected to the copper bars of the commutator. They are connected with other points of the system by means of carbon brushes. The whole machine is enclosed in a casing supporting the field magnets and the bearings. The armature of the dynamo runs on two ball bearings mounted in a waterproof housing filled with grease. They are greased during the assembly process and require no more attention.

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