How To Light A Light Bulb With A Potato

| May 30, 2012 | 2 Comments

     Did you know that you can light up a light bulb by just using a few household items and a potato? The chemical reaction between 2 different metals and the juices in the potato generate enough voltage to actually make a clock run (which uses very little energy), or a light bulb (but a very small one). The whole experiment should produce about 1.5 volts DC, but this is just the potential. This means that you might need to use several potatoes to light up a bulb, but a small LED will probably glow from just one. 

potato light bulb battery

The Experiment: First, you need to get your materials: a large potato (or 2 potatoes), two copper pennies, three copper wires, 2 zinc or zinc-plated nails, a small light bulb or LED. Cut the potato in half if you’re using a large one, or take each potato and in each make a small slit, just big enough for each penny to fit in to. Take 2 pieces of copper wire and wrap one around one penny and the other around the other penny a few times. Stick the pennies into the slits you cut before. 

Take the third piece of copper wire and wrap it around one of the zinc nails. Stick that nail into one of the potato halves. The next step is to take the wire wrapped around the penny from the half with the nail in it, and wrap it around the other nail. Take that nail and put it into the other half of the potato. Now, take the two ends of wire that remain loose (one should be from a penny and the other from a nail), and touch them to a light bulb. Voila, you should have light!

The reason this works is because the phosphoric acid (H3PO4) in the potato makes the copper and zinc react in such a way that there is an exchange of electrons that takes place between them. The potato acts more as an electrolyte, not really having a role in the chemical reaction itself. This is why it’s very important to make sure that the pennies and nails never directly touch each other inside the potato. Lee Ellen Benjamin, M.A, from San Francisco State University explains that:

“Zinc is an active metal, which reacts readily with acid to liberate electrons. The acid’s active ingredient is positively charged hydrogen, so a transfer of electrons takes place between the zinc and the acid. The zinc (Zn0) is oxidized (Zn++ ) and the acid (H+) is reduced to hydrogen gas (H2), which you can see bubbling out around the electrodes. The reaction at the penny electrode depletes the electrons from the copper and attaches them to the hydrogen ions in the phosphoric acid.

Oxidation: Zn –> Zn++ + 2e-
(Zinc looses 2 electrons)

Reduction: 2H+ + 2e- –> H2
(Hydrogen ions gain electrons)

Net Reaction: Zn + 2H+ –> Zn++ + H2
(Hydrogen gas and ‘power’) “

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Category: Brain Food

Comments (2)

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  1. this is really cool lol.

  2. hey this is really cool to be giving people instrutions to do really cool projects.

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