Electronics 101: Lesson-02 Circuit Basics

What is a Circuit?

One of the first things one will encounter when learning electronics is the concept of a circuit. In this tutorial, we are going to discuss the basics of an electric circuit in further detail.

Consider the circuit below;

The circular path which is always required to get electricity to flow and do something useful is called a circuit. It starts and stops at the same place.


In the previous tutorial, we covered the basics of Electricity and how it works, take a look at the tutorial here…

Lesson 1: Electricity and how it works


Voltage and how it works:

A battery has a specific number of volts and so does a wall outlet at our homes. Voltage is basically the measurement of the electrical potential produced by the battery or the utility grid-connected to the wall outlet. The volts in the battery or wall outlet won’t actually do anything until you use them to power a device.

What we’ve learned so far:

  • For any circuit, we know the following:
  • Voltage is potential, a voltage difference is required in order to get electricity to flow and do anything useful.
  • Electricity needs a path to flow through, which must be an electrical conductor such as a copper wire.
  • Electricity will flow from a higher voltage to a lower voltage
  • DC voltage sources like batteries always have two sides i.e. positive and negative with the positive side having a higher voltage and the negative side having a lower voltage.


Short & Open Circuits

The main reason why we build circuits, is to make electricity do useful things for us, and the way we do that is by introducing different things in our circuits that use the current flow to light up, spin motors, run and power appliances, etc.

The things that we introduce in our circuits are called “loads” because they “load down” the power supply. If we load down a power supply too much, this slows down the current flow which can damage the electronic components or even the power supply.

Let’s learn about two special cases of circuits i.e. short circuit & open circuit and knowing about these will help us tremendously when it comes to troubleshooting the circuits we build.

Short Circuit:

If we connect a wire directly from the positive to the negative side of a power supply, we create a short circuit and this is a very bad idea.

Consider the illustration below;

Why is this a bad idea?

Earlier, we learned that electricity (electrical current) flows from a higher voltage to a lower voltage and if we introduce a load into the circuit, we can be able to do something useful like light up a LED.

With a load in the circuit, the current flowing through the circuit is limited as compared to that which your device consumes, however, without any restrictor in the circuit, there won’t be anything to slow down the current and it will try to be infinite. In such cases, the power supply will provide as much current as it can which may be too much and this could burn the wires, damage the power supply, or even drain the battery.

In most cases, a safety mechanism is built into the power supply to limit maximum current in the event of a short circuit, but this is not always the case. This is why we all have circuit breakers in our homes and office buildings to prevent fires from starting in the event of a short circuit somewhere in the wirings.

The other related problem to a short circuit is when we unintentionally let too much current flow through part of our circuits which causes a part to burn out. This may not be a short circuit but it’s close and it most often happens when we use the incorrect resistor value which lets too much current flow through another component such as an LED as illustrated below;


NB: The bottom line here is that if you notice that things are of all of a sudden becoming hot or a part of the circuit blows up, turn off the power source immediately and look for possible short circuits.


Open Circuits:

This is basically the opposite of the short circuit and it’s a circuit where the loop isn’t fully connected and therefore it isn’t really a circuit at all.

Consider the illustration below;

In this circuit, unlike the short circuit we saw earlier, nothing will burn out but also the circuit won’t work either. This is most likely caused by an open circuit which is usually due to a broken connection or a loose wire.

In case you are new to circuits and you are having trouble locating an open or short circuit, a multimeter can be a very useful tool for troubleshooting. If you set it to measure volts, you can use it to measure or check the voltage at different points in your circuit and eventually find the point where voltage isn’t getting through.



We’ve just covered the basic form of a circuit and as we keep going with these tutorials, we’ll encounter more complex circuits with multiple loops and many more electronic components. One thing you should note though is that no matter how complex a circuit is, it will always follow the same rules as the basic one-loop circuit that we’ve just covered in this tutorial. In the next tutorial, we’re going to cover the difference between Alternating Current (AC) and Direct Current (DC).




Tum Kurtzman
Author: Tum Kurtzman

Computer Engineer, Ugandan Life Hacker, Tech Blogger, YouTuber, Founder & Lead Engineer at SONALABS.ORG... Tum completed his BSc. in Computer Engineering from Makerere University and you can reach him via e-mail at tum@sonalabs.org.

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