The ordinary statement that an electric current is flowing along a wire is only a conventional way of expressing the fact that the wire and the space around the wire are in a different state from that in which they are when no electric current is said to be flowing.
In order to make laymen understand the action of this so called current, it is generally compared with the flow of water.
In comparing hydraulics and electricity, it must be borne in mind, however, that there is really no such thing as an “electric fluid,” and that water in pipes has mass and weight, while electricity has none. It should be noted, however, that electricity is conveniently spoken of as having weight in explaining some of the ways in which it manifests itself.
All electrical machines and batteries are merely instruments for moving electricity from one place to another, or for causing electricity, when accumulated in one place, to do work in returning to its former level of distribution.
The head or pressure in a standpipe is what causes water to move through the pipes which offer resistance to the flow.
Similarly, the conductors, along which the electric current is said to flow, offer more or less resistance to the flow, depending on the material. Copper wire is generally used as it offers little resistance.
The current must have pressure to overcome the resistance of the conductor and flow along its surface. This pressure is called voltage caused by what is known as difference of potential between the source and terminal.
The pressure under which a current flows is measured in volts and the quantity that passes in amperes. The resistance with which the current meets in flowing along a conductor is measured in ohms.
Ques. What is a volt?