One volt is the amount of electrical potential difference across a conductor having a resistance of one OHM which makes a current of one ampere flow in the conductor. Ohm's law relates the three units: volt, ampere, and ohm.
The common flashlight cell has one and one-half volts. Commercial electricity enters one's house at either 110 or 220 volts.
Electromotive force (emf) is the pressure of electrons. Voltage is a measure of this electron pressure somewhat the same way pounds per square inch is a measure of water-pipe pressure.
A battery consists of two or more cells, connected in series; and each cell adds its voltage to the rest. Thus the common six-volt lantern battery has four, one and one-half volt dry cells. An automobile battery is made of cells of another type, the lead-sulfuric acid cell, each unit of which gives 2.0 volts. Since a car's starter motor, lamps, and spark-coil system are designed to work on twelve volts, a car battery has six such two-volt cells connected in series. Parallel-connected batteries do not increase the voltage. They are used where larger currents are needed.
The alternating current commonly used in American homes, offices, and factories comes along transmission lines from generator stations. In these lines, electric current is moved at very high voltages because less heating loss is produced in the wire this way. Long-distance lines often employ over 100,000 volts. At points along the way, the voltage is stepped down by transformers to the 110 or 220 volts used in homes and offices.
Voltages in radios may range from 150 to 1500 volts. In television sets, voltages of 20,000 volts exist at certain points. These voltages are obtained by stepping up the household voltage of 110 volts, using transformers.
Lightning and experimental machines can generate voltages of more than one million volts.
