Simple Circuits Curriculum

Section 7: Endnotes

  • 1 The actual voltage is really a little less due to the internal resistance of the battery. At this point, when students are learning to reason across the whole circuit as a system, it is helpful to think of the voltage as one number across the circuit. However, as students start to learn about more complex circuits, they will need to reason about the differences in voltage (and corresponding voltage drops) between components of the system. Therefore, we introduce the idea that voltage is the difference in charge between the battery nodes even though students may find it simpler to first think about voltage as the number of volts that they read on the side of the battery.
  • 2 Technically speaking, Ohm's Law gives an adequate explanation for parallel bulbs but only part of the story for series bulbs. From Ohm's Law, current through two bulbs in a series is half what it is through one bulb alone. But potential difference across each bulb is only half the total battery voltage as well. So half the current and half the voltage means each bulb only gets one fourth the power.