When you turn on a light switch, it connects two pieces of metal together to form a complete loop, called a circuit. Electricity flows through the circuit to power up the light, just like water in your home’s water pipes. When the light is turned off, the electricity can’t jump across the gap, so the light stays off.

There are many types of lights that we use. Some are large lights, like light bulbs. These are filled with gas and have a metal inside that glows when the electricity flows through it. Others use other gases to make the gas itself glow. LEDs are used on everything from washing machines to helicopters to tell us that something is happening. LEDs are even used in very efficient light bulbs.

Whenever there’s a power source connected to a circuit, electricity will flow. We call this flow the electric current. This is the same as when water flows through a river and we call the water flow a water current.

As long as one side of the power source (called the anode) is connected to the negative side (called a cathode) the electric current can flow through the circuit from positive to negative. Lets make a circuit and find out how electricity works for ourselves!

Our First Circuit: Let There Be Light!

Engineers have an idea of what it is the thing they need to build should do. Usually there’s a problem to solve. Our problem is pretty simple:

It’s too dark. It should be less dark.

To solve the problem, we’re going to make light with electricity. Obviously we don’t want it to be light all the time because we might want to sleep, so we need some way of switching the light on and off. Finally, we need a power source.

There are many ways to make light. There are light bulbs which you have in your home. There are LEDs that make bright light using very little power. There’s fire, but we’re not allowed to do that at Raw Hex anymore after Steve accidentally set his hair on fire.

We can’t use a light bulb as it needs mains electricity, and mains electricity is dangerous. So we’ll use an LED. If you have a HIDIOT kit, by luck you just happen to have two LEDs!

The next thing we need is a power source. A common CR2032 coin battery should do. These are used in watches and some remote controls and are easily found in supermarkets.

Finally we need a way to switch the circuit on and off. We’ll use a small piece of paper (about 2.5cm wide and 2.5cm long, or roughly 1 inch wide and 1 inch long).

Just so we know what we need, here’s a list of parts:

If you’ve bought a HIDIOT learning kit, you’ll already have the LED and resistor. If not, you’ll need to find the parts yourself. The HIDIOT kit contains two LEDs, either one will do.

Only use a 3 volt CR2032 battery. Anything else may burn out the LED, or may even cause things to get very hot, unsafe, possibly explosive. If in doubt, don’t do it.

Lets start by looking at our LED. An LED has a blob on the top (in your case, probably coloured red) and two long metal legs, one longer than the other. The long leg is the positive leg, called the anode. The short leg is the negative leg, called the cathode. When electric current flows through the LED, a small amount of the electricity is converted into light. The rest then goes around the circuit.

LEDs are greedy, and will eat up as much current as they can, but the more current they absorb, the hotter they get. This is why you must only use the CR2032 battery, as the CR2032 doesn’t provide enough current for the LED to overheat.

Our piece of paper can be quite small and goes on the negative side of our battery. We then put the LED’s cathode on top of the piece of paper, and the anode on the positive side of the battery.

All set? Let’s turn on the light by pulling out the piece of paper and pressing the LED legs and battery together with your thumb and forefingers.

If all goes well the LED should glow red. If it didn’t work, try swapping the LED legs around. If that doesn’t work, try the other LED in your HIDIOT kit, and try another CR2032 battery.

So what just happened? Believe it or not, what you’ve just experienced is almost the same as how the light switch works in your house. Our piece of paper stops the electrical current from flowing around the circuit. When you pull away the paper it’s the same as turning on a light switch. The circuit is completed, electricity flows and the LED turns some of the electric current into light. The electric current continues out of the shorter leg and into the battery’s cathode.

We know the electrical current flows through the LED and makes it light up, but how does it work? What’s pushing the current along? To understand this we need to understand four ideas about how electricity works.

You might want to take a break now, or click here to go to the next section.