Lemon Battery

Objectives

• Describe the relationship between an electron and current electricity.

Materials

• Per Pair of Students:
  lemon (and other fruit, optional)
  1 copper strip
  1 zinc strip (you can use a galvanized nail, which is coated with zinc)
  knife
  2 copper wire leads (each about 20 cm long) with alligator clips on both ends
  LED bulb with a rating of no more than 2 volts (the smaller the voltage, the better)
  wire cutters
  wire strippers

• Per Class:
  multimeter or voltmeter (optional)

Key Questions

• What happens when you connect the wire to the bulb?
• What is the power source?
• What role does the lemon play in lighting up the bulb?
• When we use two strips of the same metal, does the bulb light up? Why?
• Is water a good conductor of electrical current? Is salt a good conductor of electrical current? How do you know?

What To Do

1. Roll the lemon firmly on a counter to release some of the juices.
2. Insert the one copper strip and one zinc strip vertically into the lemon, with one end sticking out.
3. Connect one wire lead to each metal strip (electrode).
4. Connect one of the free ends of the wire leads to one of the wires attached to the LED
5. Connect the remaining free end of the wire lead to the remaining free wire on the bulb. Don’t be surprised if the bulb doesn’t light!
   
   • Hint: If you’re using an LED, it will only light if it’s connected in the right direction. Try switching direction.
   • Hint: Don’t try to test your LED by hooking it up to a commercial battery. A commercial battery will be too powerful and will wreck the LED.
6. Use the voltmeter or multimeter to check the voltage between the two electrodes. It will probably be less than 1 volt! That’s not enough to light the LED, which needs about 2 volts. Join together in groups of three or four lemons. Connect the lemons together in series (connect copper to zinc together with wire) and attach the ends to ONE bulb. Use the voltmeter to check the voltage between the free wires at the ends of the series.

​Teacher Tip: The voltage will be extremely weak. You may need at least 3 lemons per battery for any visible movement to occur on the voltometer.

Extensions

• Experiment with other fruits (e.g. oranges, grapefruits, apples, peaches, pears). Which ones produce the highest voltage? Why?
• Experiment with replacing the electrodes with two copper strips or two zinc strips and try to light the bulb. Measure the voltage and explain the results.
• Experiment with replacing the electrodes with different metals (e.g. iron and magnesium). Which combinations of electrodes give the highest voltage?