Orange batteries and dogs in PhET circuits: Pre-class overheads (November 11 – 15)

(This post is part of an ongoing, semester long series. Each week, as a lecture TA in Physics 100, I choose a pre-class overhead for each of the two lectures I help out in. I attempt to choose images that connect to the current material and that are fun and possibly provocative. Here, I keep a record of the images I choose and thoughts I have about the in-class outcomes.)

This week in Physics 100 was spent discussing circuits. Since circuits are often hidden in real life, I had more difficulty than in previous weeks in finding images that I thought could relate the content to students’ experiences. Perhaps I could have pushed some of the analogies we have discussed in class, such as heat conduction, climbing and descending a mountain, or traffic. Perhaps I could have put up an image of an electronic device. (Although, it’s hard to see how the simple R circuits we discuss relate to a complicated device like an iPhone.) What-ifs aside, the images I chose were explicitly and directly tied to the lecture material.

For the first class of the week, I used an image of a battery formed by connecting two mandarin oranges in series. I added the prompts, “What do you notice? What do you wonder?” Later in the lecture, the instructor made a battery to power an LED by connecting several lemons in series. Before the lecture, the instructor and I chatted about whether or not showing the image of the mandarin orange battery would ‘ruin the surprise’ in the lemon experiment later in class. It’s my opinion that showing the image was not a bad idea and that it may even help the students to correctly observe the lemon experiment. (As shown in this recent paper, it is important for learning that students correctly observe a demonstration.)

For the second lecture of the week, I decided to advertise the circuit PhET simulation by showing an image of an odd circuit that I made. The sim is a great tool to help students construct a mental representation of what’s happening in a circuit. During the pre-lecture time, I spoke to a few groups of students, asking them if they had been using the PhET sim to help them with their circuit homework. It was interesting to find out that almost no one I asked had actually used the sim yet. So, referring to the image on the overhead, I encouraged them to go through the worksheets from lecture and their homework with the PhET. Of course, I emphasized the fun aspect too, pointing out the dog and the battery on fire.


Reflecting on the experience with the second pre-class overhead, I can identify two important lessons:

  1. An alternative use of the pre-class overhead can be to advertise extra class resources (or even other things you might want to point out to students).
  2. My duties as a lecture TA can begin before the lecture starts, by initiating conversations with idle students.

With regards to the second item, I believe that the pre-class overhead could help facilitate TA-student interactions during the pre-lecture time. These interactions could hopefully help to motivate the students. Of course, there isn’t too much time pre-lecture, after students start to sit down and before the class begins. However, it could be that just talking to two or three different groups of students before each class is enough to motivate the students to consider the pre-class overhead, to be more interested in the upcoming class, and to perhaps be more comfortable and feel more welcome in the room. Presumably, talking to a few students during the pre-lecture is something the instructor could do also (assuming they are maybe a bit early for class and do not have too much preparation to do there).

Comment/question starters

Some possible comment starters for you:

  • A good non-obvious circuit related image would be …
  • Other possible effects of pre-class interactions with students could be…
  • There is no way pre-class interactions with just a few students could have an effect on them! This is because …
  • I’m an instructor and I do chat with students before class. I’ve noticed that this helps to …
  • I’m an instructor and I would never chat with students before class because …
  • I’m a student and I think it would be terrible if the instructor came up to me before class! This is because …
  • I’m a student and it’d be great to chat more with the instructor, so that I could …
  • A way you can use pre-class overheads more effectively could be ….
  • What is your goal with the pre-class overheads?
  • The main goal of pre-class overheads should be _____________. To accomplish this, you should …

(Mandarin battery attribution: By G43 (Own work) [GFDL ( or CC-BY-SA-3.0-2.5-2.0-1.0 (, via Wikimedia Commons.)



  1. Nice post, Jared.

    What I appreciate about this series is how helpful it’s going to be me in my own lecture TA position in the winter. Seriously! Even if I don’t get to implement a consistent “pre-lecture overhead” as you’ve been doing here, I think the idea of trying to engage with the students in simple conversation before the class starts is a great suggestion that I might have not considered. Also, the way you’re interpreting relevant education-research and turning it into practice is commendable.

    I’d be curious to hear how your students felt after the lemon experiment, having been queued somewhat to the demonstration with your image of the orange-circuit.

    1. Hi Chad, thanks for the nice comments! Stay tuned for an upcoming ‘Guide to being a lecture TA’ post, which I intend to write after reflecting on my experiences this semester. It will be great for it to be an iterative process – I will look for your input on updating the recommendations after you’ve had a chance to try things out.

      I like to believe that queuing them with the image helped them to observe the experiment better. In this case, it was probably reminding them about the system. I know that I saw a potato battery at some point in my pre-university life, so I think it’s likely most of them have too. The idea of queuing them is in line with my own experiences, though. Often, I find that it takes seeing or hearing something a few times before I realize the meaning of it. It’s possible that just flashing the image during the pre-class is enough to count as one of these ‘few times’ for the students.

  2. I like your idea of weaving the advertisement of additional resources into the pre-lecture overhead. I have sometimes used PhET simulations for pre-class assignments where the question is “Play around with the PhET sim and tell me 3 interesting or non-intuitive things that you found.” Sometimes students would send me screencasts or save files for the PhETs so there might even be an excellent opportunity to use student-generated questions or curiosities to serve as the pre-lecture overhead.

    1. It would be fantastic to use student-generated content for the pre-lecture overhead! It would send a great message to students that they can contribute to the course (especially if there was also a discussion about it). Plus, I think most students would be excited about getting their image up there.

      Is there a possible research question in there? Something like, ‘Do student-generated pre-class overheads promote a better beginning of lecture discussion?’ (‘Better’ is to be defined.)

      1. I think that might be a reasonably straight-forward research question to investigate. You could simply oscillate back and forth each lecture between TA (or instructor) generated and student-generated content for the pre-lecture overheads. And as you say, “better” would need to be defined (based on some measure of student engagement and sophistication of comments and questions).

  3. […] Talk to students before and after class. Use this time to motivate them, to advertise resources, or to get to know them and make them feel comfortable. (As thought about in a previous post.) […]

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