To start with we need to understand the structure of an atom. An atom is the basic building blocks of everything we know of, it consists of a dense central nucleus surrounded by small negatively charged particles called electrons. The nucleus contains positively charged particles called protons and neutral particles called neutrons. Normal atoms have the same number of protons as electrons and so their overall charge is neutral (as the positive particles and negative particles cancel each other out). Atoms that have a different number of protons and electrons are called ions as they are charged particles, but that’s another story.
Charged objects will exert a force on other charged objects as they are surrounded by an Electric Field. Like charges (2 positives or 2 negatives) will repel each other, and opposite charges (negative and positive) will attract. It is because of these forces that all these particles are held in place within the atom.
This is an example of the structure of an atom:
Firstly you will notice there are layers of electrons, these are called shells and we’ll look at these more closely in a minute. You will also notice that there are only 2 electrons on the first layer followed by 4 on the next. Each shell has a maximum number of electrons on it, the first shell has 2 and the second 8, there are more shells but we won’t worry about that. As the electrons are attracted to the nucleus, the shells will be filled systematically leaving spaces on the outer shell, called the Valence Shell, occupied with Valence Electrons. As this has 4 electrons on its outer shell and has 2 shells, this is the element is Carbon.
The electrons in a conductor are free to move and it’s this that allows a current to flow, and hence electricity. It’s this movement of free electrons that generates a current, the more movement, the greater current. And since movement causes heat, the larger the current the hotter it all becomes, this is why electrical appliances have ratings like 3A, 5A and 13A: because the large currents will create enough heat to melt the device, this is where fuses come in handy. The A by the way stands for Amperes (or t for short) and that is what current is measured in.
In copper (which is a very good electrical conductor), the free electrons will move easily when a potential difference is applied. The applied voltage creates a drift of electrons, these flow from negative to positive, this is called Electron Flow. However we always say that electricity flows from positive to negative, and this should remembered, this is called Conventional Flow. There is a reason for this but it’s irrelevant, just remember that electricity flows from positive to negative, but on a subatomic level the electrons are moving in the opposite direction.
It should be noted that there are 2 types of current, Alternating Current (AC) and Direct Current (DC). When electricity flows in one direction, this is Direct Current, it is at a fixed voltage level. DC is usually for small scale, battery powered devices: most of the circuits we use and teach at HobbyGenius is DC. Alternating Current flows in both directions, it alternates between a positive voltage and negative voltage (where the negative voltage is the opposite direction). AC is for large scale, high voltage devices like the national power grid and the plug sockets in our homes.
So that’s our introduction to the atom and current in a circuit. If you have any questions feel free to comment and we’ll help explain things as best as we can.
Move on to our next tutorial when we look at the difference between conductors, insulators and semiconductors.