Insert a small strip of zinc and a small strip of copper into the fruit, leave a gap of about 5cm between the two and make sure they do not come into contact with one another. Using crocodile clips and thin insulated copper wire, connect the two metals to a voltmeter. Because of the small amount of electricity created, a millivoltmeter or microvoltmeter may show a visually better sweep.
Fruits can be connected in series to create higher voltages, remember that the connections between the fruits should be zinc to copper or copper to zinc, The electricity is created because the acid in the fruit reacts with the metals creating a transfer of electrons.
Teachers will sometimes ask for class sets of this equipment, requiring a selection of different fruits so pupils can experiment with variables. Different metals can also be experimented with; aluminium, iron, lead, magnesium, carbon and tin may be required. The metal strips will need to be prepared fresh every time (because the metals will deteriorate with contact with the acids).
Fruit clocks can be purchased through lab suppliers which use the same method but have a small digital clock instead of a voltmeter. They are fairly inexpensive compared to making up new demo sets every time a teacher needs it and also shows pupils the practical aspect of making the battery.
A battery is a series of cells connected together to increase the voltage. One piece of fruit would therefore make a 'cell' whereas several connected together make a 'battery.'
Do not eat the fruit after the experiment! ? Some of the toxic metals will have dissolved into the fruit.
The contents of this page are for information only. Please refer to CLEAPSS or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.