Day 34 – Capacitors and Charge


Engineering Physics – As a re-introduction to dc circuits, I had students play with capacitors for a bit using some of my CASTLE materials. The highlight, as I expected, was when we discussed the conclusions from the above activity. About 1/2 of this class took enriched physics last year and wrote the AP Physics 1 exam. However, pretty much all students said that the charge originated in the battery. I then started to question their ideas and assumptions?

  • What is the middle of a capacitor? An insulator they tell me.
  • Can charge move through a capacitor? No, they tell me.

Hmmm…. lots of strained faces at this point. Then one student puts his hand up. “Are you saying that the battery pushes the charges into the capacitor and that the pressure in the capacitor pushes the charges on the other side, and that charges are everywhere in the wires?”

At this point I’m jumping up and down. “No! I didn’t say that! You did!”
Huge win for today.

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