Making a Battery from a Lemon

You will learn about the structure of a simple voltaic battery that converts chemical energy into electrical electrodes. Steel and copper wires are the electrodes in this battery and the citric acid in lemon is the electrolyte. A variety of citric solutions can be used as the electrolyte, including lemon, orange, grapefruit, kiwi and tomato juice. They produce battery outputs ranging from 0.5 to 0.9V, depending on the acidity of the fruit.

Materials

18-gauge copper wire (smaller gauge will work too, but 18-gauge is stiffer)
wire clippers
steel paper clip (Some people find that a 2-inch strip of zinc works better.)
sheet of coarse sandpaper
lemon
a multimeter


Develop Your Understanding

1. Measure the voltage output of your lemon battery. Can you use this battery to power an LED? If not, why? Depress mouse to view answer. Answer: No. A typical LED requires a power source of about 2 volts output.


2. The lemon battery produces very small current (about 1 milliampere). Can you think of ways to increase the output current high enough to power an LED?



Depress mouse to view answer. Answer: By increasing electrode surface areas and using metallic-tape electrodes, lemon batteries can provide enough power for an LED.



3. Record the output voltage and current values at various times. Plot the voltage and current in dimensionless quantities (V/Vinitial and I/Iinitial), where Vinitial and Iinitial are the voltage and current output at zero time.

Time (minutes)	Voltage (Volts)	Current (Amps)	V/Vinitial	I/Iinitial
0
1
1.5
2
2.5
3
3.5
4
4.5
5

4. Plot V/Vinitial and I/Iinitial data as a function of time. Can you explain the observed changes of the dimensionless voltage and current?


Depress mouse to view answer. Answer: The current and voltage are expected to decrease. rapidly because of the heat generated in the connecting wire.




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