But Where Does It All Come From?
We know how the circuit works. We also know why the circuit works. The battery applies voltage to the circuit, to make the electrons jump along. The current then flows through the circuit and the LED comes on as the electrons pass through.
We set out to build a circuit that causes a light to come on when we want it to, and we have that. That’s engineering. But there’s a question that we still need to answer. What’s in the battery that provides the voltage, and can we find it anywhere else?
So far we’ve built something (our circuit). That’s engineering. There’s another type of engineering where we pull things apart and see how they work. This is called reverse engineering.
Reverse Engineering A Battery
The first thing we can do is look at how batteries work in general. Our coin battery is called a lithium battery. Lithium batteries normally have a lithium anode, a separator and a manganese dioxide cathode. Lets take a look inside a coin battery.
Never take a battery apart. It’s extremely dangerous and could burn or even be fatal.
From left to right, the different parts are:
- The negative inner cup
- Lithium anode
- Manganese dioxide cathode
- A metal grid, used as a current collector
- Positive side metal casing
Below this is a plastic insulation ring used within the battery.
The two main parts of the battery are the two different metals with a separator between them. We’re missing something because we’ve opened it up.
If we look at other batteries, we see that they’re often based on two metals. NiCad batteries are made with Nickel and Cadmium. Alkaline batteries are often made with Zinc and Manganese Dioxide. Alkaline batteries are called alkaline batteries because they have an alkaline electrolyte made of Potassium Hydroxide.
But wait. What’s an electrolyte?
An electrolyte is a paste or liquid that can conduct an electric current. Electrolytes contain atoms that either have too many or two few electrons, called ions. The ions float around in the electrolyte either being bloated or hungry for electrons.
If you remember earlier, our electrons move around the circuit and the current flows in the opposite direction. It’s the current that causes the LED to light up, but the current is produced by the movement of the electrons.
When a conductor is exposed to an electrolyte a chemical reaction occurs. Zinc interacts with the electrolyte and gives up some of it’s electrons. This leaves holes in the zinc for electrons to fill if they come from elsewhere. This makes Zinc an anode.
When copper is exposed to an electrolyte, it attracts electrons. This makes the copper have too many electrons. This makes Copper a cathode.
If we can link the Copper cathode to the Zinc anode via our circuit then the extra electrons will travel from the cathode to the anode through our circuit, to fill the holes and light up our LED along the way. To keep the current flowing we need to produce new holes on the anode, and new electrons on the cathode. That means the two metals need to be connected to the electrolyte, but not directly to each other (except through our circuit).
What To Do Next
There are electrolytes in fruit and vegetables. In fact there are so many electrolytes in some fruit and vegetables that you can make batteries with them! Don’t worry, you won’t blow anything up trying it out. Just don’t eat the fruit afterwards!
You can use the LED in the HIDIOT kit, but you’ll need to get some copper nails, some galvanised nails, some fruit and some copper wire. It’s a lot of fun, and worth trying with different fruit and vegetables. Start with citrus fruits like lemons and try a few different ones like bananas and potatoes.
There’s a really great article about fruit batteries here.
If you’re not quite sure about making batteries with fruit, SciShow has saved you the trouble, and MahoganyNerd investigated which fruit (and vegetables) produce the most electricity.
We showed you the insides of a coin battery so you don’t have to take one apart, but did you know you can make your own coin battery using actual coins?