Experiment 5: Let’s Make a Battery
34 Chapter 1
How much current is being generated in your lemon battery? Set your meter
to measure milliamps, and connect it between the nail and the penny. I mea-
sured about 2mA, but got 10mA when I used some #10 stranded copper wire
instead of a penny and a large mending plate instead of a roofing nail, im-
mersed in a cup of grapefruit juice. When a larger surface area of metal makes
better contact with the electrolyte, you get a greater flow of current. (Don’t
ever connect your meter to measure amps directly between the terminals of
a real battery. The current will be too high, and can blow the fuse inside your
meter.)
What’s the internal resistance of your lemon? Put aside the copper and zinc
electrodes and insert your nickel-plated meter probes into the juice. I got a
reading of around 30K when both probes were in the same segment of the
lemon, but 40K or higher if the probes were in different segments. Is the resis-
tance lower when you test liquid in a cup?
Here are a couple more questions that you may wish to investigate. For how
long will your lemon battery generate electricity? And why do you think your
zinc-plated electrode becomes discolored after it has been used for a while?
Electricity is generated in a battery by an exchange of ions, or free electrons, be-
tween metals. If you want to know more about this, check the section “Theory:
The nature of electricity” on the previous page.Cleanup and Recycling
The hardware that you immersed in lemons or lemon juice may be discolored,
but it is reusable. Whether you eat the lemons is up to you.