The design of electrical circuits has to ensure that all the required elements of an electrical system operate safely and effectively. This involves various safety features which seek to control the electrical current flow, and an important example of this is a resistor. Resistors are found in almost every electrical circuit and often built into other components.
What is a resistor?
A material with no resistance at all is effectively allowing current to flow freely through it, but the more resistance a material has, the harder it is for current to flow through it. A resistor, therefore, is a passive component which resists the flow of current in a circuit. Fixed resistors have a resistance value in Ohms which is a fixed value that will not vary. You can also have variable resistors whose resistance value can be changed. The amount of current that flows into a resistor is exactly the same as the amount of current flowing out of it, but importantly the resistor won’t allow any more current flowing through it than the value of the specific resistor (using Ohm’s Law, ie. Voltage = Resistance * Current).
However, a resistor acts to reduce the current flowing through the whole circuit, because you can add resistors in series, which means you add up the sum of the value of all the resistors connected in this series. Therefore the current flowing through the whole circuit will be lower than if there were no resistors at all. Using resistors we can build a circuit to have the currents and voltages we want, such as building a circuit to power a motor or to light up an LED bulb. In other words, the resistor gives us control over what happens to the circuit.
How do resistors work?
Resistors ensure components receive the proper voltage in a circuit by creating voltage drop. Each component (such as a motor or an LED bulb) requires a specific voltage to power it. However, if one component in a circuit requires less voltage to power it than another component in the same circuit, you need to build resistance into the circuit to control the current flow, otherwise a power overload will damage the component. This means you can install resistors into the circuit design to create voltage drop, which is the slowing down of the current charge using resistance, so that you can create appropriate voltage at each component stage in order that the circuit operates safely and effectively.
Where resistors are connected in series we can use them to control the flow of current through a circuit. If two or more resistors are connected in series this means they are connected after one another, and the combined resistance is the sum of all the resistance values in the series.
Resistors are usually made from materials such as copper or carbon, which are effective in preventing electrical charge passing through them. Resistors will protect components against voltage spikes much in the same way as a circuit breaker or a fuse will. So with an LED bulb, for example, this is sensitive to high currents and will become damaged if there is no resistor in the circuit to control the flow of electrical current. So resistors work along with fuses and circuit breakers to protect the circuit and hence the electrical system.
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.