Voltage, current and resistance are the three core elements of electrical law, so to understand the basics of electricity and how circuits work, you need a fundamental understanding of the difference between voltage, current and resistance, and how these three concepts function.
What is voltage?
It is easiest to explain electricity using an analogy, such as water flowing through a pipe. Voltage is effectively the ‘push’ that makes electricity flow, so in the water pipe analogy it is the water pressure that makes water flow through a pipe. Similarly, voltage is the force that creates current and therefore makes electricity flow through a circuit. You need a power source to create this voltage push, which would be either a batter or a wall socket in most cases. Voltage is measured in volts, and the higher the volts you have, the more potential you have for creating and moving current.
What is current?
Current is the amount of electrons moving through a wire, in the same way that you can control the amount of water flowing through a pipe. Current is therefore the rate at which electricity flows through a wire or circuit, and is measured in amperes, or amps. The number of amps in a circuit is telling us how much current is moving through it, and just as you can control how much water flows through a pipe, you can control how much current flows through a circuit, ie. through controlling your voltage. Therefore, current and voltage have a direct relationship.
What is resistance?
Resistance is an opposing force which restricts or slows down current flow in a circuit. Using the water pipe again, resistance would be a narrow pipe which makes it harder for water to flow, or someone squeezing the pipe to make it narrower. A large, wide pipe has very little friction to resist water flow, and similarly different circuits, components and sizes of wire have different values of resistance. Resistance is measured in ohms.
So, in summary, voltage is the force that makes electricity flow, current is the amount of electricity that is flowing and resistance is anything that slows down the flow of electricity.
How do voltage, current and resistance work together?
The relationship between voltage, current and resistance is defined by Ohm’s law. Ohm’s law is the fundamental principle of electronics and defines the relationship between these three core components.
This is written as:
V = I/R
This can be explained as voltage equals current times resistance. Voltage and current have a direct relationship, in that if you create more voltage (push) it creates more current, assuming the amount of resistance remains the same. Current and resistance have a different relationship. If you increase the resistance, this reduces the current flow, assuming voltage stays the same.
Ohm’s law can therefore be rearranged to find the component you don’t know in a circuit, based on what you do know. So:
- To find voltage (V):
V = I × R - To find current (I):
I = V / R - To find resistance (R):
R = V / I
This effectively means that, as long as two of the core values are known, you can always use Ohm’s law to find the third. This is useful when direct measurement isn’t possible, such as in a live circuit when you can’t disconnect components.
Please note that this section is for information purposes only. Anyone using equipment referred to in this section must be suitably qualified and/or experienced within the respective field. If in doubt before use, please consult a qualified electrician or engineer & thoroughly read all instruction booklets.