Activity: Lemon Battery

On SCOPE's Robotics episode, you saw Bronte making a battery from lemons. Here's how you can make your own at home. First up are the instructions for a one-lemon battery. Further below, we give you a bit more of a challenge - making a more powerful battery that will actually light up a lightbulb!

What you need

Rest the tips of the two wires on your tongue. You should feel a slight tingle.

What you need for the Lemon Battery Challenge

First failed attempt at the Lemon Battery Challenge!

By using four lemons you should be able to see a faint glow from the LED.

• A lemon
• A clean paper clip
• Around 10cm of clean copper wire with the plastic coating stripped off
• Wire cutters

What to do

1. Roll and squeeze the lemon on a bench top to loosen the juices inside - don't squeeze too hard.
2. Unfold the paper clip and stick it halfway into the lemon. Using wire cutters you may like to clip the paperclip to about 3 cm.
3. Stick the piece of copper wire halfway into the lemon. Make sure the pieces of wire are close together but not touching.
4. Rest the tips of the two wires on your tongue. Make sure you have plenty of saliva on your tongue.
5. You should be able to feel a slight tingle on your tongue, or at least get a strong metallic taste.

What's happening?

That tingle you feel is electricity from the lemon. The electricity is travelling up one wire across the saliva on your tongue and back through the other wire. Your tongue is the switch that makes the electricity flow. Most paper clips are galvanised steel wire, which means the wire is coated in zinc. By using different metals, zinc and copper, you create the flow of electrons.

Lemon juice is an acid. The metal in the paper clip reacts with the acid to produce an electric current. It's the same process as the electricity produced in a battery.

You have made a voltaic battery, which changes chemical energy into electrical energy. The battery is made up of two different metals (the steel paper clip and the copper wire). These are called electrodes. Electric current enters or leaves the battery through the electrodes. The liquid in the lemon becomes the electrolyte, which is a solution that can conduct electricity. Touching the electrodes to your tongue closes the circuit and allows a small electric current to flow.

Applications

A battery you buy from the shop contains a paste, which is either acidic or alkali. Two different metal connectors, called electrodes, are pushed into this paste. When you put them into a battery-powered machine and turn on the switch, the electricity flows from one electrode through the machine and then through the other electrode. If you don't have both parts of the battery connected, nothing happens.

The Lemon Battery Challenge

Lemons produce only a very small current, about one milliamp. This is not enough electric current to light a torch bulb. By using a couple of lemons you might get 1.5 volts but the current will not be strong enough to power a bulb. You may have enough current to power an LED (Light Emitting Diode). For the lemon battery to work, a very specific diode needs to be used. These diodes involve low current (2 mA) and low voltage (2.3 Volts). Your local electronics shop should be able to supply these. If your lemon battery doesn't light an LED you could try making your electrodes bigger by using copper sheet instead of copper wire, different metal electrodes like zinc or magnesium, or more than two lemons in series. Four lemon batteries in a series should create a voltage of 3.50 volts. The connecting wires go from "+" to "-" on each battery .

You will need

• 4 lemons
• 4 pieces of copper or copper wire
• 4 pieces of paper clip or zinc plated nails
• 4 wires, preferably with alligator clips on the ends
• A light emitting diode (LED) with a low voltage rating
• Wires cutters (to cut copper or steel as needed)

The zinc-plated nails can be found at most hardware stores. They are also called "galvanized" nails. The zinc plating, which is there to prevent rusting of the steel nail, gives them a shiny look. The wires with clips can be found at hardware stores or at electronics suppliers.

What to do

1. Place a nail and a piece of copper into each lemon.
2. The copper is the positive (+) terminal and the nail is the negative (-) terminal.
3. Using the wires and clips, join the four lemon cells together, so that the nail of the first lemon is connected to the copper of the second lemon, and so on.
4. Add wires and clips to the first piece of copper and the last nail. The lemons are now connected in series.
5. Clip the wire from the first lemon to one leg of the LED and the wire from the last lemon to other leg. Hopefully you will see a dim glow from the light.
6. You might need to turn the lights out in the room or place your LED in a dark space, like a film canister to see the glow.