This practical may require:
Citrus fruits tend to work well- lemons, limes, grapefruits and other acidic fruits and vegetables.
- Various fruits
- Various metal strips
- Millivolmeter or microvoltmeter
- Crocodile clips
- Insulated copper wires
Students may insert a small strip of zinc and a small strip of copper into the fruit, leaving a gap of about 5cm between the two and making sure they do not come into contact with one another. Using crocodile clips and thin insulated copper wires, they may then 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. Digital multimeters will give a more precise reading.
Fruits may be connected in series to create higher voltages, remember that the connections between the fruits should be zinc to copper or copper to zinc, making up a circuit.
The electricity is created because the acid in the fruit reacts with the metals creating a transfer of electrons. Teachers may sometimes ask for class sets of this equipment, requiring a selection of different fruits so pupils may experiment with the different types. various metals may also be varied; aluminium, iron, lead, magnesium, carbon and tin may be required. The metal strips will need to be prepared fresh every time (because the metals may deteriorate through contact with the acids).
Fruit clocks can be purchased which use the same principle but have a small digital clock instead of a voltmeter. Some also have pots where fruit juice or dilute acid may be contained. If using these pots, make sure the electrodes are set deep into the liquid and that they do not come into contact with each other. If they do it will cause a short in the circuit and electricity will not flow. Fruit clocks are fairly inexpensive and have the added advantage of showing students a practical use for the battery. The clocks generally work for a long time with just a small amount of fruit or acidic liquid although they do need regular cleaning and replacement metal strips.