What Does a Resistor Do?

Daniel Attoe
Daniel Attoe

Updated · Oct 16, 2022


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Resistors are among the most common and essential electrical components in the world. They are widely used in various appliances and devices—from microwaves and heaters to light bulbs and mobile phones.

Even though they are a part of (almost) every electrical device in the world, most people are still oblivious to their workings.

That’s why today, you’ll get to learn all that is important to know about them. What does a resistor do, how does it work, and what is it made of?

Let’s find out!

What Is a Resistor?

A resistor is an electrical component that resists the flow of current. In other words, it opposes the passage of electrons through a circuit. This opposition is known as resistance, which is why its symbol is R.

Although resistors are passive components, they play an important role in electronic circuits. By controlling the amount of current that flows through, resistors can help to protect other parts from damage and ensure that electronic devices operate as intended.

Their value is typically measured in ohms.

What Does a Resistor Do?

A resistor’s primary purpose is to introduce resistance into a circuit, which can help control the current and voltage flow.

By controlling the flow of electricity, they can help regulate the voltage and current in a circuit. So we can say that resistors play a vital role in ensuring electronic devices operate safely and efficiently.

Another resistor function is creating different effects in a circuit, such as producing a delay or generating a sparkling sound.

By understanding how resistors work, engineers can create all sorts of amazing devices we use in our everyday lives.

Their precise control over current and voltage makes them indispensable in any circuit. What’s more, their ability to protect other components makes them essential for ensuring the reliability of any electronic system.

How Does a Resistor Work?

We’ve covered a resistor’s definition and function. Let’s see exactly how it works:

Electrical resistance measures the difficulty electrons have in flowing through a material.

Some of them, like metals, allow electrons to flow freely, which is why they make good conductors. In contrast, others, like rubber or glass, are more resistant. That’s what makes them good insulators.

In a typical electrical circuit, current flows from the positive terminal of a power source through the resistor and back to the negative terminal. As you can see, it acts like a roadblock in the circuit, forcing the current to slow down.

When choosing a resistor for a circuit, it's essential to select one with the appropriate features.

If it’s too large, it won't provide enough resistance to the current, which may result in overheating. On the other hand, if it is too small, it will create too much of it, and the current may not flow at all.

By selecting the proper size resistor in a circuit, engineers can control the amount of current flowing through and prevent damage to components.

The basic principle here is called Ohm's law, named after German physicist Georg Simon Ohm. It states that the current passing through a conductor is directly proportional to the voltage applied to it, provided the temperature remains constant.

The law goes like this:

I = V/R

where I is the current in amperes, V is the voltage in volts, and R is the resistance in ohms.

By varying the R-value of a resistor, the formula shows we can control the amount of current flowing through it.

How to Read Resistor Color Codes?

The bands on a resistor represent its resistance value and tolerance. This is called a “color code,” one that’s used to indicate the component’s properties.

In a four-band resistor (the most common type), the code consists of four colored bands, each representing a different number. The first two stand for the first two digits of the value, while the third indicates the multiplier.

Resistor color chart

For example, a resistor with the color code brown, black, brown, and gold would have a value of 100 ohms. To calculate it, simply take the first two digits (in this case, 10) and multiply them by the multiplier (once again, 10). This gives you a final result of 100 ohms.

When reading resistor color codes, you must also be aware of the tolerance. That’s what the fourth band represents. For example, if it’s silver, the tolerance would be +/- 10%. The actual value then could be anywhere between 90 and 110 ohms.

Finally, it's worth noting that some resistors come with fifth or sixth bands. In the five-band version, there are three significant values, a multiplier, and a tolerance. In the six-band one, the sixth represents the temperature coefficient, useful for high-precision resistors.

However, these are less common.

What Are Resistors Made Of?

Now, let's focus on what exactly resistors are made of.

You can classify these components based on their materials.

Carbon Composition (CC) Resistors

Carbon composition resistors are created by mixing carbon with a binding agent and then pressing the mixture into a solid rod. The resistance value depends on the carbon to binding agent ratio.

CC resistors are ideal for low-power applications due to their low cost and stability. However, they are also less precise than other options and tend to drift over time.

Wirewound (WW) Resistors

As the name suggests, these are made of a length of wire wrapped around a core. The most common wire material for this resistor is manganin, although others like nichrome and copper-nickel can also be used. The R-value depends on the type of wire, its length, and cross-sectional area.

Wirewound resistors work in high-power applications because they can dissipate large amounts of heat.

Metal Film (MF) Resistors

Metal film resistors are constructed by depositing a thin metal layer onto a ceramic or glass substrate. The R-value depends on the type of metal used and the thickness of the deposited layer. MF resistors are more precise and have better temperature stability than CC ones.

They are excellent options for precision applications such as audio equipment.

Thin Film (TF) Resistors

Thin film resistors are made by depositing a thin layer of metal onto a substrate, similar to MF resistors. However, this layer is much more delicate, typically only a few micrometers thick. Both the TF resistor material used and the thickness of the layer are responsible for its resistance.

They offer high precision and stability, making them ideal for critical applications, such as medical equipment.

Foil Resistors

Foil resistors are designed by sandwiching a thin layer of metal foil between two pieces of glass or ceramic. The R-value depends on the type of metal used, the thickness of the deposited layer, and the length. These are precise resistors with excellent temperature stability.

They are used in high-precision applications such as medical equipment.

Wrap Up

Resistors are components used to control the flow of electricity in a circuit. They are made of different materials, including carbon, metal, and thin film.

The type of material used determines the component’s resistance value, precision, and stability. Their applications vary immensely, from low-power electronics to high-precision medical equipment.

So there you have it—now that you know what they do and how they work, you can start experimenting with them in your own circuits.


What is a resistor in a circuit?

Resistors are small electrical components. On a circuit board, resistors help regulate electric current flow.

What does a resistor look like?

Resistors vary in size and shape, but they all have two terminals (or leads) that allow electricity to flow through them. Their body is made of a material that resists the flow of electricity. Usually, the component’s R-value is displayed on its body.

Why do we need resistors?

First, what does a resistor do? It controls the amount of current flowing through a circuit. So why is it needed? Because it helps prevent damage to sensitive electronic components and ensures that everything works as intended. Without resistors, electronic circuits would be much less reliable and often fail.


Daniel Attoe

Daniel Attoe

Daniel is an Economics grad who fell in love with tech. His love for books and reading pushed him into picking up the pen - and keyboard. Also a data analyst, he's taking that leap into data science and machine learning. When not writing or studying, chances are that you'll catch him watching football or face-deep in an epic fantasy novel.

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