Excerpt from Information: Elementary Electricity, Motor Car Electric Systems and Delco Light
In a similar way we may say that electricity exists in a state of no pressure, but we can give to it a pressure by means of a generator, and when we allow the electricity to escape, as we may term it, it gives up its pressure, then it is, like water, giving up energy and doing work.
The amount of work that can be done depends upon the pressure and the rate current flows. We know that electricity is invisible, yet there is pressure behind it in one state and it flows under this pressure. We cannot measure the rate of flow in gallons per hour as we do in a water system; instead, we measure the rate it flows in amperes. We have said that electricity to flow must have pressure behind it to cause it to flow. In a water system water flows under a certain number of pounds pressure. In an electric system current flows under a certain number of volts pressure.
When a wire or any substance is used to transmit current from one place to another it is called a conductor. These conductors offer a resistance to the flow of an electric current therefore, we must have some means of measuring this resistance. The resistance offered to the flow of current depends upon the kind of metal used as a conductor, its area and length. The three terms just mentioned - the volt as the unit of electric pressure, the ampere as the unit of electric current and the ohm as the unit of electric resistance are related to one another - this relationship being known as Ohm's law. See Ohm's Law.
When we speak of electricity we should regard it as a means by which energy can be transmitted from one place to another. Energy exists in nature in various forms, such as coal, crude oil (from which gasoline, kerosene, etc., are derived), natural gas, etc., and by using up some of this "stored" energy, work can be done. All mechanical and electrical devices are simply "energy transformers." They are operated by energy in one of its forms, and during the time work is being done the energy is changed into another form.
For example: - A gasoline engine will run only as long as the supply of energy (in the form of gasoline) lasts. When this supply runs out, the engine stops. Part of the original energy is changed into a form of energy called heat, which is gradually absorbed by the air and objects with which the heat comes in contact.
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