If the coil be described by the maker as a 4 volt coil, it should be worked by two cells of a storage battery or four dry cells. The voltage of the latter will be somewhat higher, but since their internal resistance is also greater, the current delivery will be about the same. Most coils are made to operate on from 4 to 6 volts.
6. It is a mistake to use a higher voltage than that for which the coil is designed, because it does not improve the spark and the contact points of the vibrator will be burned more rapidly, moreover, the life of the battery will be shortened.
CHAPTER XII
THE DYNAMO
The dynamo is a machine which converts mechanical energy into electrical energy by electromagnetic induction.
The word dynamo is used to designate a machine which produces direct current as distinguished from the alternator or machine generating an alternating current. In a broader sense, the word generator is used to denote any machine generating electric current by electromagnetic induction; the term therefore includes both dynamos and alternators.
Operation of a Dynamo.—A dynamo does not create electricity, but generates or produces an induced electromotive force which causes a current of electricity to flow through a circuit of conductors in much the same way as a force pump causes a current of water to flow in pipes. The electromotive force generated in the dynamo causes the current of electricity to pass from a lower to a higher potential in the machine, and from the higher back to the lower potential in the external circuit; that is, the dynamo generates electrical pressure which overcomes the resistance or opposition to the current flow in the circuit. The pump produces a mechanical pressure which, for instance, may be used to force water into an elevated reservoir against the back pressure due to its weight.
