All of the things that we touch and experience are made of something we call matter. Matter is made of tiny particles that are so small we can’t even see them. We call these atoms. Atoms themselves are made up of even smaller particles, one of which is called an electron. Electrons are negatively charged particles that orbit around atoms, like planets orbiting the sun.

When we apply energy to atoms, they start to get quite excited. When some atoms get excited, the electrons start to jump from one atom to the next. These types of atoms are called conductors, because they conduct electrical current. These atoms are normally found in metals.

Atoms that don’t let the electrons jump are called insulators. Common insulators include rubber and wood.

To make the electrons in a conductor move, all we need to do is give them a push with some energy. In electricity, we call this force Voltage.

Lets take a look at our circuit again. Pop the paper in between one of the LED legs and the battery. Now have a think about our electrons. The paper doesn’t conduct electricity, so the electrons can’t be passed on. That’s why the LED doesn’t light up.

Now pull out the paper. The light comes on because the electrons are moving through the circuit. When the circuit is fully connected, we call this a closed circuit. When the circuit is disconnected or something blocks part of the circuit from being connected, we call this an open circuit.


Voltage is the force the pushes the electrons along. Imagine you’re at a birthday party, playing pass the parcel. Everyone stands in a line passing the parcels along to the music. The parcels are the electrons. As the music goes faster, the parcels are passed more quickly. When the music stops, the parcels stop moving. At the party, in electrical terms, the voltage is the music. The people in the line are the conductive atoms.

Voltage is measured in volts. Our CR2032 battery supplies 3 volts, which is enough to make the LED come on. The HIDIOT uses a mixture of 3.6 and 5 volts in different parts of the circuit.

Lets take a look at our circuit again and try to understand the party going on between your fingertips. Pop the paper in between an LED leg and the battery.

The music isn’t playing.

This is the song that the atoms are getting excited about:

Derp! Derp! Derp!

Come on and pass electrons.

Derp! Derp! Derp!

We’re positively charged!

Pull out the paper and try to imagine the electrons being passed from one atom to the next in beat to the music. You can sing it if you like.

With low voltages like our coin battery circuit, atoms are a bit slow and sleepy. If you were too excited, put the paper back in, then pull it out and try again but slow and sleepy.

At 5 volts, it’s pretty upbeat party music. At 9 volts the atoms are getting a real workout and at 12 volts they start getting pretty sweaty after a while.

Mains electricity can be 110, 220 or 240 volts depending on where you live. Never play with mains electricity. The atoms get so excited they get bruised and burned, and mains electricity could really hurt or even kill you.

Sometimes being slow and sleepy is perfectly fine. Building things that do exactly what they’re meant to do, in exactly the way they’re meant to do it is called engineering. We built a circuit to make the light come on, and it works! You’re now officially a junior engineer!


If voltage pushes electrons along, resistance does the opposite. It restricts the flow of electrons, reducing the current in the process. Imagine a hose pipe being used to water a gardern. If we pinch the hose pipe, there’s less space for the water to flow through. Turning the tap up to push more water out is the same as increasing the voltage, and more water flows through even though you’re still squeezing the hosepipe the same way.

Electrical resistance works the same way as water resistance. We measure resistance in Ohms.

The most commonly used electrical component we use to manage resistance is called a resistor. You’ll find some in your HIDIOT kit. They’re the bits that have the multicoloured stripes and a gold band at one end.


We already know a little bit about current. We know it’s much like the flow of a river but used when talking about electricity. We know that the electrical current flows from the positive side (the anode) to the negative side (cathode) of a circuit. A strong current means there are a lot of electrons flowing through the circuit. When you increase the voltage, you increase the current.

Weirdly, the electrons themselves flow in the opposite direction from negative to positive. This is because of some fairly complicated physics. All we need to know is that when we talk about electric current, we talk about it flowing from positive to negative.

Putting it all together

Now we know about electrons, voltage, resistance and current we can understand what happens when we pull the paper away from the circuit. Set up your circuit again so you can play along.

We know that our circuit is made of conductors - materials that conduct electricity and allow the electrons to move around when we apply energy.

We know that metal is a good conductor because our circuit works and is mostly metal.

Paper is a bad conductor of electricity. When we put it between an LED leg and the battery, the light doesn’t come on because the paper won’t pass the electrons on, blocking the flow of electrons and electrical current.

When we pull the paper away, the LED leg makes contact with the battery and completes the circuit. At this point we can say the circuit is closed.

The voltage in the battery pushes the electrons around the circuit. The electrical current flows from the positive side to the negative side.

The LED greedily gobbles up all of the electrical current it can consume to emit red light.

The electrical current flows because our circuit is closed. If we push the paper back in or pull an leg away from the circuit, the flow stops because the circuit is now open.

At this point you might be thinking this is all well and good. The atoms are having a great time, the electrons are moving, but where does the electricity come from? Let’s take a look in the next section.