How to Make a Lemon Battery

Adam Camp: Hi! I am Adam Camp. Today, we are learning about how to make a battery. In this clip, we are going to take an ordinary lemon and turn it into a battery powerful enough to illuminate an LED. In order to start, you need to take your lemon, put it on the table and gently roll it back and forth. Now, what this is going to do, is it's going to produce the electrolyte base you require in order to make a good battery. In the lemon's case the citric acid inside of the lemon is going to act as that electrolyte in order to produce the bridge between the copper and the zinc.

To start, after you have rolled your lemon on the table, we are going to take one of your galvanized steel nails and insert it into one end of the lemon. That's going to produce our cathode. On the other side of the lemon, we need to take a knife and make a small incision, so that we can insert our penny into the lemon to produce our anode. Make sure that you don't insert it too far or you won't be able to get your penny back out. Now, we can take a multimeter and measure what the voltage is coming out of our lemon and then we can assess how many of these lemons we are going to need in order to power our LED. In this case the lemon is producing about 4.0 volts, which certainly is a lot less than we were getting out of our potatoes and I am not terribly happy with the voltage coming out of this. In order to increase the voltage coming out of a lemon, what we can do is increase the amount of surface area that the copper is coming in contact with the citric acid electrolyte. You can take one of your pieces of copper wire and use some of your steel wool to make sure that no oxidation is inhibiting its contact with the citric acid and wind it down with the copper wire a few times. Then if you take the copper wire and wrap it around your finger and produce a nice small tightly knit coil and what this will do, is it will give you ample surface area inside of the lemon to hopefully increase our voltage from 0.4 volt to something higher. Then go ahead and insert that copper coil into the hole that you produced for your battery and you can insert that much further because you have a nice little piece sticking out. Now, what we have is a lemon with a galvanized nail as the cathode and piece of copper wire as the anode and if we go ahead and measure the voltage coming out of our battery now, you will see that it is surprisingly a lot higher, it is almost twice as much voltage that was coming out of using a penny that we are getting coming out of a piece of coiled wire.

If you remember from our first lecture, the battery required in order to illuminate an LED, it needs to produce 1.5 volts and about 10 milliamps of current. What we have now is a battery that is producing about 0.9 volts. So theoretically, we should be able to put two batteries in series in order to increase the voltage high enough to drive an LED. In order to connect the two lemon batteries in series, we are going to connect the cathode of one battery to the anode of the other battery. What you are left with is a single cathode and a single anode and if we measure the voltage coming out of our new lemon battery, it should be somewhere around 1.7 to 1.8 volts. We are getting about 1.84 volts. If we take this new battery and connect it to our LED, we will see, it is illuminating a lot more than the six potato batteries we were using. We get essentially the same amount of voltage out of two batteries made out of lemons than we would out of six batteries made out of potatoes.

That is it for how to make a lemon battery; coming up next is the clip on how to make a battery out of a film canister.