engineer-in-wonderland
Rooting around in the fascinating stuff at the bottom of a draw labelled 'Engineering - Junk Miscellaneous'. Delving amongst the delightful...

The power of lemons

Lemon battery I can remember some disappointment when I was little.

I had an ‘electrical set’ made for children and it included some containers, electrodes, and copper sulphate with which to make a battery.

Excitedly, I made the battery and used it to power a light bulb, but no light came out.

And however I checked it over, still no light came out.

It is a wonder that I was ever interested in chemistry or electricity again.

Come forward a few (!) of years and such experiments are encouraged in school, it seems.

Eight year-old Ella Ray has to make electricity for her school project and, being a good dad, one of the Electronics Weekly team has been helping out a bit to make sure she doesn’t have a disappointing time.

And just to be clear here, there is no cheating going on, parents are supposed to be getting involved.

Anyway, for all you parents out there who might need to do something similar, here are his findings:

Ingredients:
galvanised nails (zinc electrodes)
wire cut from single-strand mains cable (copper electrodes)
coins (more electrodes)
lemons
A slightly ancient low-power red LED
A set of croc clips from Maplins

Method:
Make six lemon cells and connect them in series.
Connect the LED to make a circuit, try the LED both ways around.

Lemon battery LED lightResults:

Light!

But at first, the light was barely visible.

Closing the gap between the electrodes reduced the light further. (Anyone know why? – reply below please).

Expand the distance between the electrodes, and light increases noticeably.

More light from a lemon batteryReplace copper wire with 2p pieces: dramatically increased light – enabling a reduction in lemon count to four with no reduction in light.

Good Luck Ella

Tags: copper electrodes, copper sulphate, electrodes

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2 Comments

  1. steve bush
    February 11, 2014 10:13

    Hi Mr Kurt.

    Sadly, we no longer have chemists in the UK.
    Universities shut their courses as they were expensive to run and no one was interested – SO much more fascinating to do media studies.
    The stalwarts of the industry have retired, or are close to it.
    - or so the radio told me. I hope I am wrong.

    Maybe there is an electro-chemist out there who could help?

    I remember plotting field lines with that carbon-loaded conductive paper. Maybe this is a job for that technology?

    The copper wires were rather thin – around 1mm diameter, and the coins seemed to work better – and are not pure copper.

    Anyone help here?

  2. Steve Kurt
    February 07, 2014 18:17

    More current when the electrodes are moved apart?? Sounds like a question for “Chemical Engineers Weekly”? :-)

    Most batteries use a fairly thin separator between the plates, don’t they? Of course, the plates have huge surfaces. I’m trying to think of a way that greater distance between the electrodes would reduce current density or increase the useable surface area, but I’ve got nothing. Weird…

    Any comments on the effect of using multple electrodes in a lemon? Increasing the electrode area ought to improve the current.