Did you know that you can light a light bulb with potatoes? And that, in general, some food products are capable of doing that? In this article we will explain the physical phenomena by which we can turn the shopping list into–electricity!
The electrical circuit: let’s explain it in a simple way
Understanding electricity is no small matter. One is dealing with a phenomenon that everyone has daily experience of on a macroscopic level, but there is no opportunity to see with one’s own eyes what happens inside a metal wire or understand the motions that happen in a hot plate while cooking or in the glowing wire of a hair dryer. Scientists themselves have taken centuries to interpret electrical phenomena and their implications. The discovery of the electron as a negative charge and a fundamental particle certainly gave a breakthrough to experimental science and initiated new scientific models and theories.
The understanding of electrical phenomena involves a strong abstraction component and relies on the construction of appropriate models to describe electrical conduction. We are stimulated daily to use electrical appliances; yet, we are unable to explain the nature of the electrical phenomenon!
Before we dive into the experience of observing the electrical phenomenon, let’s start with the main question: what are the physical conditions necessary for an electrical circuit to occur? What circuit elements are essential to build an electrical circuit?
To explain this we go back a few centuries and meet Alessandro Volta, an Italian physicist and chemist whose name we certainly all know. In 1800, Volta made the invention of the battery public by sending a letter to Joseph Banks, president of the Royal Society of London.
What does the invention of the electric circuit consist of?
Alessandro Volta constructed a column consisting of pairs of copper and zinc disks, stacking them on top of each other and separating them by a cloth soaked in dilute sulfuric acid.
Zinc and copper, in contact with acid solution, become negatively and positively charged each other by chemical reactions that we now know by the name of oxidation-reduction, or
redox
. An electric field is thus created: each charge in fact generates an electric field around it, and each of these charges can exert a force on other charges that are close to it.
Since zinc and copper are close to each other in pairs, their charges exert a force on each other, which causes them to move. By moving, they gain energy!
Each pair of soaked and charged copper and zinc disks thus gives rise to what in physics is called a “potential difference.” Having stacked several pairs, the potential differences of each pair add up because they are interspersed by the diskette soaked in dilute acid that allows the charges to shift. Thus, at the extremes of this stack, the potential difference resulted as the sum of that of all pairs of copper and zinc.
Volta connected through a copper wire the zinc disk at the upper end of the “stack” with the copper disk at the lower end, and thus obtained a continuous passage of electric current circulating from the positive pole (the copper) to the negative pole (the zinc), returning to the positive pole after passing through the inside of the stack.
Modern batteries, although quite different, exploit the same principle. To the battery you then simply connect a light bulb or any electronic device et voila, ignition.
Can potatoes constitute an electrical circuit? How?
Zinc and copper react chemically with potato flesh in different ways. Zinc carries out chemical reactions such that positive charges accumulate on it. Conversely, negative charges will be concentrated on the copper wires.
The potato itself does not produce energy, but because it contains ascorbic acid, this in contact with copper and zinc allows electrons to pass from one side to the other; in short, it acts as a bridge.
That’s right, theascorbic acid in the potato behaves like the sulfuric acid in Volta’s battery, allowing charges to pass through. This phenomenon is also known as a “redox” reaction, and it is capable of turning on and keeping electrical artifacts in operation.
One or two potatoes are generally not enough to light a light bulb: not enough potential difference is accumulated. We use at least four potatoes, by now we have realized that by connecting them in series their potential differences add up!
All clear? Good!
And now–to the workshop!
The ingredients for our experiment
- Four potatoes
- Zinc bars/nails
- Copper rods/wires
- Electrode/lamp
- Metal cables with clamps at both ends
Components to build the electrical circuit can be bought from the hardware store or on the Internet by typing “electrical circuit kit” and relying on the most common online sales platforms.
Proceedings
- Wash and dry the potatoes
- Arrange them on a plane and insert, in each one, a zinc nail (or rod) + and a copper wire –
- We now connect the positive (zinc) poles of one potato with the negative (copper) poles of the next potato using clamps. Let’s move on to the second potato and connect it with the third using the same logic: positive pole with negative pole. By connecting more than one potato in series, in this case let’s stop at the third, we will get enough potential difference to light a small 1.5-volt bulb!
- Once we have connected three potatoes in series, we then move on to connecting the bulb: we connect a clamp to the copper of the first potato we used, which will have remained unconnected. The other end of that clamp we will need to connect to one of the two electrodes of our bulb. We use one last wire to connect the zinc of our last potato: one clamp on the metal and one on the uncovered bulb electrode.
- The moment we “close” the circuit, there goes the light bulb!!!
Can only potatoes conduct electricity?
The answer is: of course not. You can experiment with different foods you have at home, such as apple, tomato, cheese. But also liquid substances such aswater, cream or milk.
The world is an immense scientific laboratory, all we have to do is … experience it!
