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Acting out circuits

November 4, 2012

On Friday, I had students acted out (i.e. be the charges inside) different circuits. I’ve done this as a quick demonstration before but this is the first time I’ve devoted the entire class to the activity. I split the class into two groups of 10-20 students each and gave each group the task of acting out the following circuits:

  1. One battery connected to two light bulbs in series
  2. One battery connected to two light bulbs in parallel
  3. Two batteries in series connected to one light bulb
  4. Two batteries in parallel connected to one light bulb

Before turning students loose, I had one group watch while I walked the other group through how act out a simple circuit with one battery and one light bulb. With pictures denoting the battery and the light bulb, I placed the battery on one table and the light bulb on another and said that the circular path around both tables represents our circuit. I put a pile of dried pinto beans on top of the battery to represent energy and told students that as charges, they should pick up energy from the battery and deposit that energy in the light bulb as they walk around the circuit.

I gave students the following rules to guide their “circuit theater”:

  • Charges cannot bunch up anywhere in the circuit.
  • The “voltage” of each battery is two beans.
  • The brightness of a bulb is determined by how much energy each charge transfers to the bulb and how quickly charges are passing through the bulb.

I asked students to specifically think about how fast they should be walking and how bright the bulb would be. I suggested that students use the PhET Circuit Construction Kit simulation to check their ideas about bulb brightness and the speed of charges in the different circuits.

What went well…

Overall, I think the activity was a success. The students had not used the PhET simulation that shows the charges before so this was really the first time they thought explicitly about where and how the charges are moving in different circuits. I think this helped some students to better understand series vs. parallel connections. I think this activity also helped to make the concepts of current and voltage more tangible.

What was challenging…

I need to really think about what exactly I want students to get out of this activity. For sure I want students to gain a better understanding of current and voltage and series vs. parallel connections. What I’m still debating is how far I want to push this in terms of providing explanations for the relative brightness of the bulbs in each circuit or the relative lifetimes of batteries in different circuits. For both of the parallel circuits the current will be different at different parts of the circuits. I’m not sure how far I want to delve into this. Understanding this idea provides a lot of explanatory power but it isn’t an obvious idea and I need to think about whether I can guide students through this idea without too much work/time.

I learned something…

If you add a second (identical) battery in series with the first battery, the brightness of the light bulb will increase by a factor of four. This makes sense because not only is each charge transferring twice as much energy to the bulb as it passes through, but the charges are also passing through twice as fast. Of course, this is precisely what the equation power = voltage*current says. I certainly knew this equation and knew the answer but I never really had a physical picture or mechanism associated with this equation before I sketched out my circuit theater activity.

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