You Just Never Know What Will Inspire a Student

Spoons used as resistors in series (left) and in parallel (right).

In my high school physics course designed for homeschooling, I cover the standard topics that are considered important in preparing a student for university-level physics. One of those topics is resistance in electrical circuits. Unless you are dealing with exotic substances at very low temperatures (superconductors), all materials that conduct electricity resist the flow of electrons to some extent. A good conductor has a low resistance; a poor conductor has a high resistance. The amount of resistance in an electrical circuit and the voltage of the power source determine the amount of current flowing through the circuit, so it is important to be able to calculate a circuit’s overall resistance.

When resistors are connected so that the electricity must flow through each one of them, we say that the resistors are hooked in series. Notice how the spoons are connected in the left-hand photograph above. If I hook a battery up to the handle of the right-hand spoon and the head of the left-hand spoon, electricity would have to flow through both spoons to get from the negative side of the battery to the positive side. That tells you the spoons are hooked together in series.

When resistors are connected so that electricity has a “choice” about which resistor to travel through, we say that the resistors are hooked up in parallel. Notice how the spoons are connected in the right-hand photo above. If I were to hook a battery to the handle and head of the bottom spoon, the electricity would only have to travel through one of the two spoons to go from the negative side of the battery to the positive side. That tells you the spoons are hooked together in parallel.

Whether resistors are hooked in parallel or series has a profound effect on the electrical current running through the circuit. In most high-school physics courses, there is a laboratory exercise where students construct a circuit with resistors in series and then measure the current. They then take those same resistors and construct a circuit with them in parallel and measure the current. The current in the parallel circuit is significantly higher. This laboratory exercise typically involves an electronic device call a “breadboard,” resistors used in electrical circuits, and a power source, like what is shown in the picture below:

Resistors in a bread board connected to a power source (click for credit)

Since my course is designed for the home, it doesn’t make sense to have the parents purchase such equipment for just one or two experiments. As a result, I have the students use stainless steel spoons (not silver spoons) as resistors. They connect the spoons together with wire and tape, and then they use a battery to power their circuit. They connect their circuit to the top of an incandescent flashlight and use the brightness of the light as an indicator of the current. The light shines much brighter when the spoons are connected in parallel, because the current is greater.

I have always disliked that experiment. It is time-consuming to set up, it is clunky, and it just looks incredibly amateurish. It works, and it adequately demonstrates what it is meant to demonstrate. It just doesn’t look as “scientific” as the kind of experiment that would be done in a school. This week, I was discussing that experiment in one of my online physics courses, and I told the students that the experiment is annoying, and it might take some trial and error to get it working, but it will work if you are careful. I was then surprised to hear a student say:

This is the experiment that made my brother an electrical engineer…He had this experiment set up for two weeks in our basement. He worked on it in the basement for an hour every day once he got done with school…He just raves about it.

I was taken aback. A clunky, amateurish circuit using spoons as resistors inspired him to start making his own clunky, amateurish circuits, and that inspired him to become an electrical engineer!

Once I got over my surprise, I started thinking. I wondered if any student had ever been inspired by the “breadboard” version of the experiment pictured above. I decided that it probably had inspired at least some students. Then I wondered if the clunky, amateurish experiment in my book was more effective at such inspiration, less effective, or pretty much the same. It’s possible that since the components of my experiment are common objects found in the home, it makes doing variations on the experiment much easier. That might make it more inspiring. However, the ease with which a breadboard and laboratory-based materials work might make doing variations on the experiment more interesting, which might make the breadboard version more inspiring.

I really don’t know whether or not one version of the experiment has more potential for inspiring students. However, I do know is this: I would never have thought that this experiment would inspire anyone to become an electrical engineer. Nevertheless, it did so in at least one case. It just goes to show that at least sometimes, you never know what will inspire a student!

3 Comments

  1. John D says:

    I like the spoons. I also really like the batteries made from cups of lemon juice or the ones from pennies and nickels.

    I think doing science without a scientific apparatus is so fun! Some students might experience a little less fascination with a breadboard since it has been manufactured for the purpose of the job. But household materials can really be lightning rods! It’s also a reminder that at one time it’s all people had to do science.

  2. David H says:

    I really liked the electrolysis experiments we did as part of our Chemistry class. We used a 6V lantern battery for power, and tried seeing how much bubbling we could produce with several different kinds of liquids. We had good results with orange juice, I recall.

  3. Jordan says:

    I found this experiment annoying as well but that is the case with similar electrical experiments that require using wires and batteries. Connections with tape and rubber bands are prone to disconnecting and improper contact. All my stainless steel utensils had low enough resistance to make the series/parallel demonstrations unclear. Most of the experiments in the text are straightforward but this one really benefits from purpose built parts. Battery holders, wires with clips, resistors, etc. are all fairly inexpensive but I guess that’s situational.

%d bloggers like this: