How Electrical Current Flows


Throw a switch on the wall and light will flood the room. Click the power button on your TV remote and sound and pictures appear. Electricity controls your heating and air conditioning as well as the rest of your world.

How does it work? How does it get to your light? Notice some things right off about electrical current flow. It’s fast, nearly instantaneous. Also, the current that began flowing the moment you closed that switch was just produced by the generator of the power station perhaps hundreds of miles away. Electricity cannot be stored; it must be generated as needed.

Electric current is the flow of negatively charged particles called electrons. To understand this, examine how the material world is made. This line of thought began several thousand years ago. Most of the inventive or development progress on the makeup of matter is from the last 150 to 200 years. Matter was thought to be made up of many, many small particles called atoms.

We cannot see the structures of atoms very well. However indirect measurements are made to give some information. Physicists use their imagination to develop models to represent the unknown. Then using measurements and theories the models are modified until they can explain a varity of physical phenomena without contradicting itself. John Dalton started it with his atomic theory and Ernst Rutherford furthered it with his nuclear atom. The resulting model is a small solar system. The sun is the atomic nucleus which contains neutrons with no charge and positively charged protons. Surrounding this sun are planets representing negatively charged electrons in various orbits.

Some atoms like hydrogen have only one electron and others have many orbital electrons. There are enough electrons in orbit to balance the positive charge of the nucleus and leave the atom electrically neutral.

Copper atoms are bound in a crystalline lattice. The outer orbits of these atoms contain electrons not strongly attached. These free electrons, as they are called roam about at random in the lattice.

If a copper wire was attached to the negative pole and the positive pole of a battery, we would find that when a switch was closed an electrical stress was placed across the wire. The free electrons would begin to drift toward the positive pole (opposites attract) where there was already a deficiency of electrons. The excess of electrons at the negative pole of the battery would begin to move into the wire, contributing to the build up of an electron stream or current.

As a free electron was drawn forward it would find a vacancy in the next atom left by another free electron. The one at that location previously would bump the next one down and so on. Picture a line of buckets at a fire. Instead of passing each bucket down to the next man, one would dump water in his bucket and so on down the line. The water would move toward the fire, but not the buckets. Individual electrons in a wire carrying a current move slowly at about 0.01 cm per second for a 1 amp current in copper. The impulse of the electron movement travels in the circuit at nearly the speed of light or 186,000 miles per second.

Any discussion of physical quantities like electricity should cover measurements. How many amps, or amperes are there in a circuit? That’s what we talk about when we measure electricity flow. However, the flow of electricity is actually measured in coulombs. (Most quantities like this one are named after people that were in on the discovery of electricity. In this case that would be a Frenchman named Charles Augustin de Coulomb, circa 1770s. France was very much into the sciences in that period.) One coulomb equals the number 628 followed by 16 zeros, electrons. One ampere equals the flow of one coulomb per second.

According to the electron theory the direction of electricity flow is from negative to positive in the conductor. Our own American inventor Ben Franklin got it wrong. But then he had one chance in two to get it right. According to Franklin, electricity was a fluid. Rub two objects together and electric fluid flows from one to the other. The object that gained the fluid was called positive. The one that loses fluid was called negative. The electric flow would be from a point of high pressure to one of low pressure. The error became firmly established by the time the electron or atomic theory was established. But it will not be a problem as long as you are consistent. A battery can be thought of as pumping the pressure inside it to a high level at the positive pole. The same would be true of a generator. The electric power industry uses the old method and in some ways it is easier to deal with during analysis of current flow. The electronics industry will usually use the flow of electrons as it will nearer suit their applications.

Other materials will have plenty of orbital electrons on the outer reaches of their atoms but they will not be free electrons. It will take more energy to loosen them up. These materials will be classed as insulators as they will not be used for current flow. They will be used instead to separate or protect current carriers from touch.