Here at Science Buddies we get a lot of questions about our veggie power project.
This is a classic and perfectly legitimate science experiment where you
build a battery using potatoes or other fruits or vegetables like lemons or
onions and use it to power something like a tiny LED or one of those little
solar-powered calculators. However you have to be careful because there are a
lot of videos online claiming you can use these batteries to power something
much larger like a full-size light bulb or charging your cell phone. What we're
going to do in this video is go over the science of how these batteries actually
work and how some of the hoaxes behind them are perpetrated so you can decide
for yourself when you see one of these videos if it's real and if it's
something you can reasonably expect to try for a science fair project. First
let's talk about voltage and current and what we can reasonably expect from one
of these batteries. Here's where it helps to read the small print. If we look at a
common LED light bulb we'll see that it's rated for 120 volts and 142
milliamps. We're not worried about the difference between alternating current
and direct current for now. If we look at a cell phone charger again there's a lot
of small print here but the part that we care about is the output to the phone
which for this charger is rated at five point one volts and two amps. Let's
compare that to what we measure from the potato battery using our multimeter. If
you don't know what a multimeter is or how to use one check out the link to our
multimeter tutorial in the video description. If we set the multimeter to
measure the battery's open circuit voltage
we get less than a volt, about 0.9. If we set it to measure the short-circuit
current [multimeter dial clicking]
we get less than a milliamp
about point 4 milliamps or 400 micro amps. That's a lot less than what
will be needed to power either the cellphone charger or the light bulb.
Now, voltages do add if you combine batteries in series and currents add if
you combine batteries in parallel. So in theory you could combine enough of them
to get enough voltage and current for either the cellphone charger or the
light bulb but you're going to need a lot of them. So if you see a video
claiming to charge a cell phone or power a light bulb with just a single potato
it's probably a hoax. Now let's talk about battery chemistry. You don't need
to fully understand the chemical reaction and get the basic idea so don't
worry if this diagram scares you. If you do want to read about the chemical
reactions in more detail click the link below the video. The basic concept is
that there's a chemical reaction between the metal electrodes, usually
copper and zinc, and the electrolyte, or the liquid inside the potato. In order
for a potential difference to be generated and for current to flow the
electrodes need to be two different metals. If the electrodes are the same
metal then there's no potential difference generated and no current will
flow. Again we can demonstrate this with our multimeter. On the left here I have a
potato battery with one copper electrode and one zinc electrode and as I
demonstrated before I can measure the short-circuit current of this battery. On
the right I have a battery with two copper electrodes and if I switch the
multimeter probes over to that one
we can see that I measure zero current. This gives you something else to check
for when watching a video. The pins on the inside of a USB cable are all coated
in the same type of metal, usually a copper alloy although more expensive
cables might be gold-plated. If I plug that cable directly into the potato I
only have one type of metal contacting the electrolyte so there's no voltage
difference and no current can flow. The same concept applies to the base of a
light bulb which has two different contacts but they're both the same type
of metal, so again I can't just plug the light bulb directly into the potato and
expect it to generate a voltage. Next always be wary of things you can't see
clearly or that aren't explained well in the video, for example I've framed this
shot to imply that the same USB cable that's plugged into the potato is also
charging the phone, and I have my phone screen on to prove that it's charging.
However what you can't see out in the frame is that this cable isn't plugged
into anything and this is a completely different cable that's plugged into the
phone's regular charger. So if you can't see something clearly don't trust it.
What about the light bulb? This one might seem a little more convincing at first.
Here I have a potato with a hole cut in the top and what appears to be a regular
light bulb. When I insert the bulb into the potato and screw it in tight, it
lights up, and this time it looks like I don't have any hidden wires or cables.
The secret here is that this is actually a prank light bulb. I have a second one
here that I've disassembled and when I remove the base you can see that it has
a double-a battery and a smaller light bulb hidden inside. When something
conductive like a piece of metal or the electrolyte inside a potato closes the
circuit by touching the two contacts on the outside of the socket it causes the
bulb to light up, making it appear as if the bulb is operating with no true power
source. You can just buy these online or even build one yourself by carefully
disassembling an old light bulb, so this gives you something else to watch out
for when you're seeing a video. There could be a hidden battery inside.
While this double-a battery is pretty large and we would be able to see it if
we had a clear light bulb instead of a frosted one, there could be something
even smaller like an LED and a coin cell battery
which would be small enough to conceal inside the base of the bulb itself.
Finally be on the lookout for any claims about free energy. There is no such thing.
There are a lot of pseudo-scientific claims online about magnets and free
energy or perpetual motion machines so a video might tell you to do something
like wrap a magnet in a coil of wire and plug the wires into your potato. While it
is possible to generate electrical current using magnets and wire, it
requires relative motion between the two. They have to be sliding back and forth
or rotating with respect to each other, and we have several projects on
the Science Buddies website that demonstrate that. However just wrapping a
magnet in wire and plugging it into your potato like this won't do anything.
Let's recap and talk about the things you need to look out for when trying to
determine if a fruit or veggie power battery video is real or fake. Number one:
voltage and current. Find out what the voltage and current required to power
the device shown in the video actually are, and compare that to the voltage and
current you could expect from the number of fruits or vegetables shown in the
video. As we saw from our measurements from a single potato we got less than a
volt and less than a milliamp, so it would take hundreds of them to power a
single light bulb. Number two: electrode materials. Remember that the electrodes
need to be two different metals, so if the video just shows a regular cable
being plugged directly into a potato, then the pins on the cable are all the
same metal, and you won't get the chemical reactions you need to generate
current. Number three: is there anything you can't see clearly or that isn't
explained in the video, like wires going off the screen or something that could
have a hidden battery inside. Number four are there any pseudo-scientific claims
about free energy or perpetual motion. These things are impossible and a video
claiming to demonstrate them is not credible.
Can you think of other ways to prove whether or not a video is a hoax? Let us
know in the comments. For links to the resources and projects we've discussed
in this video, check the description below the video or the links at the end.