Monday, 15 July 2013

Making a Lemon Battery and How Does it Work?

The lemon battery is one of the most popular science experiments for kids. It features in Episode 2: B is for Battery of Circuit Playground by LadyAda from AdaFruit Industries. When my kids watched this episode they of course wanted to make a lemon battery.

It's a quick and fun experiment to do and kids can get really involved with it. When their cousin visited we had fun doing the experiment. We used a mixture of lemons and limes - any acidic citrus fruit will work nicely.

You will need:
  1. Lemons, limes other citrus fruit
  2. An LED or other low power electrical output
  3. A galvanized (zinc) Nail for the negative electrode
  4. A piece of copper wire or a copper Penny for the positive electrode (British pennies and two pence pieces work, modern US pennies don't actually have much copper in.)
  5. Connecting wires - we had some jumper leads with crocodile clips
  6. (Optional) a multimeter to measure output
N for Nail and Negative
P for Penny and Positive

Watch the B is for Battery episode of circuit playground to see how to set up your circuit. A useful mnemonic is N for Nail and Negative, P for Penny and Positive.

The experiment worked well for us. It was a very hands on way for the children (aged 4, 6 and nearly 7) to see a circuit in action and also to see the effect of adding more fruits in series.

We used a multimeter to measure the voltage with one lemon and then again as we added more lemons.

We tried to light the LED each time and got a faint glimmer with 3 fruits and a light that was very visible with the lights down once we had five fruits. (My older son wouldn't let us use the third lime as he wanted to eat it :)

How Does a Lemon Battery Work?


For very young children, the explanation in the Circuit Playground video is probably sufficient: the electrons want to move to the positive terminal.
"The electricity is not in the lemon." 
But for older kids, it's worth going into more detail about the chemical reaction that releases the electrons. I recommend this video from SciShow which explains the science. It's very quick so you might need to pause a few times to give kids a chance to take it in.

The video covers the prevalent misconceptions that people have about the lemon battery experiment and explains the science including electro-negativity and the ionic solution in the lemon. It's well explained and about as simple as it can be.

 The video also gives you an idea for a further experiment. You don't actually need multiple lemons to create more power, you can just add more electrodes to the same piece of fruit! This is obvious when you understand how it works, but it's easy to blindly follow the regular way of doing things (as we did.) If we'd thought of that we would have had spare fruit to make lemonade. Oh well. Next time.

Need more ideas for science experiments for kids? This book by high school science teacher Tom Robinson will give you lots of ideas.

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