How does a resistor work?

Many of your MakeCrate projects call for resistors of various strengths in the circuits, so you may be wondering what a resistor does, how they work, and what happens if you leave them out.

Our article “How does an LED Work?”  introduced the concept of a conductor– a material that easily carries electricity- and an insulator– one that prohibits the flow of electricity. Different materials can conduct electricity more easily than others. Sometimes we want to reduce the flow of electricity, and introducing materials that slow down the flow can help with this. This is where resistors come in.

Let’s start with some vocabulary:

Electricity is the flow of electrons, which are negatively charged particles.

Voltage is the difference in charge between two points in a circuit. Voltage is also theforce of an electrical current.

Current measures how fast the electrons are flowing.

A simple way to understand the difference between voltage and current is to think of a tank of water draining through a hose attached to a hole in the bottom. Here, the water is acting like the flow of electricity. The voltage is the amount of water pressure, and the current is how fast the water flows.


Resistance measures a materials ability to resist the flow of electrons through it.

If the width of the hose at the bottom remains the same, then by adding more water to the tank, the water through the hose flows faster. Similarly, adding more voltage to a circuit increases the current.

However, if the hose is replaced by a smaller hose, the same amount of water pressure produces a slower flow of water. The size of the hose provides resistance, and reduces the current. A resistor in a circuit plays the same role, reducing the current through the components they are used with.

How do resistors resist?

The resistors in MakeCrate projects are through-hole resistors, designed with two flexible ends for bending and inserting in a breadboard. The core of the resistor is made of a helix, or spiral, of conductive material wrapped around an insulating core. The material is very, very thin, which forces the current to slow down to pass through, providing resistance. To increase the amount of resistance, the number of loops in the spiral can be increased.

(image courtesy of

What happens if I don’t use a resistor?

If the current through a component is too much for the component to handle, it can overheat the component and possible damage it, or it could cause damage to your microcontroller (Arduino). LEDs will burn out quickly if not used with proper resistance.

If you want to safely see a the effect a resistor can have on a circuit, build a circuit like in your “Make Some Noise” project, but instead of connecting the buzzer to ground with a wire, use a resistor. You’ll see that the reduced current causes the buzzer to be much quieter.

To learn how to tell what resistance a particular resistor has, see the post here.

For more info about resistors, check out this article from the web.