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In Fruit Power we generated electricity with some lemons. Your challenge is to make a better battery based on fruits or vegetables. You may leave the fruit intact, as we did with our lemon battery, or extract the juice as we did with the Super-size Cell.
Our lemon batteries used zinc and copper as electrodes. You could try other metals. Our experience with the Super-size Cell also indicates that the size of the electrodes matters.
A grapefruit electric cell with
zinc and copper electrodes.
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Only a small part of each
electrode is in the grapefruit.
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We tried some experiments with grapefruits.
First we used zinc and copper strips, pushing them far into the grapefruit. Using a multimeter we recorded 0.85 Volts and 0.4 milliAmperes. We suspected that the power of the cell would be affected by how much of the electrodes’ surface area was in contact with the grapefruit. To test this theory we pulled the electrodes out so that only their tips were in the grapefruit.
The voltage was 0.75 V, close to what it was before, but the current was only 0.1 mA.
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Next we tried two grapefruit cells in series.
With two grapefruit cells in series we recorded 1.7 V and .46 mA. Voltage doubled while current remained about what it was in our original cell with the electrodes pushed all the way in.
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Right: Two grapefruit cells in series. The zinc electrode of one cell and the copper electrode of the other are attached to the multimeter. The remaining two electrodes are connected to each other with the white wire.
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Next we tried a parallel connection.
Two grapefruit cells wired in parallel. The two copper electrodes are connected to each other with the red wire, and then to the multimeter. The two zinc electrodes are linked together and to the multimeter with black wire.
With the two cells in parallel we recorded 0.85 V and 0.9 mA. Voltage was about the same as with a single cell, but current was about double.
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Right: A grapefruit electric cell with zinc and copper electrodes.
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Finally, we tried different combinations of metals for the electrodes.
We used a single grapefruit and different combinations of electrodes. Here’s what we found
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Some of the electrodes we used.
From left to right:
aluminum, iron, lead, zinc and copper.
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| Metals |
Voltage in Volts |
Current in milliAmperes |
Nickel and Zinc
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0.9
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0.28
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Lead and Zinc
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0.8
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0.42
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Carbon and Zinc
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0.8
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0.25
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Aluminum and Zinc
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0.45
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0.08
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Iron and Zinc
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0.5
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0.32
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Aluminum and Copper
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0.35
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0.09
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Aluminum and Nickel
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0.25
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0.06
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Now you try it. How much voltage and current can you get from a fruit? Can you light a lamp? Can you drive an electric motor? Share your results.
Download a pdf of this Engineering Challenge. |
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