How Does a Resistor Work?

A resistor is one of the basic types of electronic components. Resistors have two terminals and a semiconductor, such as carbon, in the middle. A semiconductor is just what it sounds like: something that conducts electricity but not that well.

While conductors like copper and gold are used in circuits to let electricity flow freely, a semiconductor is used to provide some resistance to the flow of electricity. That is why a resistor has that name.

When electricity flows through the semiconductor, some of it is turned into heat. The higher the voltage, the higher the energy is.

Heat of a Resistor

When electricity flows through a resistor, some of it is turned into heat. In most circuits, this heat is just wasted energy that is cast aside or is blown away with a fan. In some devices, however, the heat produced by the resistor is the main purpose of the circuit. Electric stoves, for example, use large resistors to produce a lot of heat to cook your food.


Electricity is measured in voltage (V) and amperage (A). The voltage can be thought of as the pressure of the electricity, and the amperage as the amount of electricity flowing through the circuit. Voltage, amperage and resistance are related by the equation V = IR. At a set voltage, amperage gets lower as the resistance gets higher.

If you think of a circuit as like a pipe carrying water, it's easy to understand why resistance lowers the amperage. If you put in narrower pipes without changing the water pressure (voltage), it will decrease how much water can flow through the pipe at once amperage.


Most resistors have a set value indicated by coloured bands around the resistor. These bands will also tell you the "tolerance" of the resistor. That means how accurate the value is. For example, a resistor with a value of 100 ohms and a tolerance of 10 per cent will be between 90 and 110 ohms.

Other Types

Other types of resistors are used for special purposes. Variable resistors are used to tune radios, control the volume on stereos and dim lights. There are also photoresistors. These only resist current when light is shined on them. Thermisters change value depending on how hot they are.