The Very Spring and Root

An engineer's adventures in education (and other musings).

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Lesson Plan: Intro to Parallel Circuits

I’ve been wanting to upload more lesson plans and materials that I think worked well — like everything else, its just a matter of finding the time.


The attached are a lesson plan and a handout for how I did the introduction to parallel circuits. At this point in the unit, we had already covered the conceptual understanding of what voltage, current, and resistance area. We had already covered Ohm’s Law as well, both activity-based and mathematically.

I have removed the following from the lesson plan:

  • Mention of or planning for individual students. Normally, in addition to planning for all students in general, I am preparing for particular students who tend to need additional prodding to focus, often have clarification questions, or perhaps need additional language assistance. 
  • The section on planning for individual students with learning disabilities, since the plans would necessarily detail confidential information about my students.


My students had not done series circuits yet. The decision to start with parallel came after some thought — I wondered if there are good reasons why series circuits a usually taught first. I really couldn’t think of any that didn’t also have an analog on the parallel side. For example, in a series circuit, it is usually intuitive why the current is the same through all components (there is only one path for the charges to take).

However, understanding why the voltage drops in a series circuit have to add up to the total battery voltage (proportional to their resistances) requires more thought (and a good understanding of what voltage physically is). On the other hand, in a parallel circuit, the idea that the current in each branch should sum to the total entering and leaving the battery is easy to visually demonstrate. But why should the voltage across all components never change, no matter how many you add or remove (within reason)?

I figured it was six one way, half a dozen the other and went with parallel first for the novelty.


These are free to use, modify, and distribute. Please credit me and/or this blog if you use it for something, and I’d love to hear any revision suggestions for next year or reports on how it went with other students! 

Lesson3.1A-ParallelCircuits [pdf]

Lesson3.1A-Handout [pdf]


Students in general pieced the important concepts together well. One thing that surprised me was that one group seemed to be able to use the data they were getting in the lesson to validate an incorrect model of parallel circuits: that it was always the closest resistor to the battery that got the most current. I realized 1) that this was not a student idea that I had anticipated, and 2) that the setup of the lab allowed this alternative conception to be reinforced (note that the resistor with lower resistance is, in fact, closer to the battery on the circuit diagram).

I asked that group to test out their idea by swapping the resistor positions, telling them to predict what would happen first. They conferred and said that “it was probably about fifty-fifty” on whether or not their theory would be disproven by the new data. They were able to discover that the current depends only on the relative value of the resistances.

I then reframed the post-activity discussion to center on this student reasoning/discovery instead of my originally planned questions. In a way, this was serendipitous — I got students to demonstrate for their peers what real science looks like. We have an initial model that attempts to explain something we observe, we ask ourselves what we need to do to validate that model, we attempt validation, and then revise our model. That meta lesson was possibly more important in the long run than the actual content of parallel circuits.

The next day, we followed up with discussion, reading, and applying mathematical relations to what we learned in the exploratory activity.