We all learnt at school in our science class that electricity is the flow of electrical power or current through a conductor or circuit. But electricity does not actually exist as an electrical quantity it is a commonly used generic term given to the movement or flow of electrical charge through a conductor. For example, we say that a river has a current flowing in it but this current is actually the movement of the water. If the water is stationary then there is no current flowing in the river and this is the same for electrical current. Electrical current results from the movement or flow of electrical charges from one point to another with the word current meaning the “flow of charge”.
Electrical charge is produced when free electrons leave the outer orbits of their respective atoms and move in a controlled direction from one atom to another through the conductor as a result of a force or energy being applied to them. This movement of free electrons through a conductor is known as drift which constitutes an electrical current flow. Then electrical current can be known as the rate of movement of charge.
All conductors such as metals contain large amounts of electrons that are loosely connected to the nucleus of their respective atoms and so can easily move through the material from atom to atom. Therefore metals are full of charge making them conductive as opposed to insulators whose electrons are held tightly to their nucleus preventing them from moving. In some metals such as copper there is an abundance of these free electrons that randomly move about from atom to atom thereby making copper highly conductive.
So why do we not get an electrical shock when we touch a copper pipe?. Well, this random movement of electrons from atom to atom does not result in a current flow as the electrons are constantly moving about in all different directions at once cancelling each other out so their combined movement in any one direction is zero. This random unorganised movement results in the overall electrical charge of the material being zero making it electrically neutral so we could say that the electrical charge in the copper pipe is uncharged.
However, some of these free electrons can line up together on the outer surface of the copper pipe as they are restricted from moving about causing the surface of the metal to become negatively charged. Since the electrons are not moving the surface generates a negative static electrical charge known commonly as “Static Electricity” or simply electricity at rest.
Connecting a battery to the copper causes all these free electrons to stop floating about, line up and move in the same direction resulting in an orderly flow of charge from one point to another and therefore a current. Then electrical current has a definite direction. We always think of electrical current flowing from the positive battery terminal to the negative battery terminal and we call this movement “conventional current flow”. The reality is the reverse, electrons move in the opposite direction as they are attracted to the positive pole of the battery and are repelled by the negative pole. Then this direction is called electron flow.
An electrical current that flows in one direction only all the time is said to be direct current (dc), while an electrical current that alternates back and forth in direction of flow is said to be an alternating current (ac). We measure the flow of charge in terms of amperes, abbreviated to “A” or just simply “amps”.
The amount of electrical charge that passes a point in a circuit at any one time is measured in COULOMBS abbreviated to “C”, with one coulomb of charge flowing per second being equal to one ampere. One coulomb is approximately equal to an excess or deficiency of more than 6 trillion electrons, 1 coulomb = 6.28 x 10^18.
So going back to our original question of “what is an electrical current” we can now say that an electrical current is an orderly flow of electrical charge through a conductor or circuit and which is measured in amperes.