Understanding Voltage, Current, and Resistance
To begin understanding electronics, you need to understand what voltage, current, and resistance are. You also need to have a clear understanding of how they relate to each other.
A unit of measurement is simply a way for us to compare things. For example, we often use pounds and ounces to measure weight or gallons to measure volume. We will use different units of measurement in electronics to help us compare things too. Do not let the terminology trip you up. It really does not need to be that complicated.
At the most basic level, Voltage simply represents the difference in electrical pressure (also known as potential) between two points. A common example is a battery sitting on a shelf. Nothing is connected to it, but the pressure difference between its positive and negative terminals is still there. You can attach a meter to it to test how much voltage is there. Volts is the unit of measure we use when talking about voltage. As shorthand, we simply use the capital letter "V". A higher Voltage has more pressure than a lower voltage. It is the voltage that causes electricity to move through circuits.
Current is the actual movement or flow of electricity. We can measure how much current is flowing with a meter. Amps is the unit of measure we use when describing how much current is flowing and we use the capital letter "A" for short. The higher the amps, the more current that is flowing. We cannot look at a circuit and see current flowing; however, to be a good technician, you must learn to visualize it in your mind.
Resistance is a term used to represent how easy or difficult it is for current to flow in a substance. It is very difficult for electricity to flow through wood because it has a very high resistance. Things with high resistance are called insulators. One of the most common insulators used is PVC, which is commonly used as the insulation to cover wires.
Most metals have a very low resistance, so it is easy for current to flow through them. Things with very low resistance, like copper, are called conductors.
There are also some special devices you will learn about later that are called semi-conductors. These are special types of devices that we will talk about in later lessons.
Resistance can also be measured with a meter and the unit of measure for resistance is Ohms. The short hand for Ohms is the omega symbol "Ω". A higher ohms value means the component has a higher resistance to current flowing through it.
| Term | Description | Unit of Measure | Shorthand |
|---|---|---|---|
| Voltage | The amount of pressure that is trying to move electricity between two points. | Volts | V |
| Current | The movement of electricity through a circuit | Amps | A |
| Resistance | The amount of opposition to movement of electricity. | Ohms | Ω |
Now that we understand what voltage, current, and resistance are, we can start examining how they relate to each other. We will do this by holding one of the three at a constant value and examining how the other two are related.
If resistance is a constant value and does not change, an increase in voltage will cause the current in the circuit to increase. Increasing the voltage is increasing the pressure which will push more electric current through the circuit. Decreasing the voltage will cause a decrease in current because there is not as much pressure pushing the current.
If instead we hold the voltage constant and adjust the amount of resistance, we can see its effect on current. If we decrease the resistance, then current flows easier, even though the voltage did not change. If we increase the resistance, then it is harder for current to move and the current flowing decreases.
As you can see, adjusting either the voltage or resistance will have an effect on current. In a couple of lessons, we will come back to this and start looking at actual voltage, resistance, and current.