5F20.50 Series and Parallel Light Bulbs


Kirchhoff's voltage law, Kirchhoff's current law, power, resistance


A 6-V battery powers a circuit with two parallel branches on a board. Several wires and light bulbs plug into the board to make various series and parallel circuits. The brightness of the bulbs changes depending on the circuit configuration.



  • [1] Circuit board (two designs available)
  • [5] Wire banana plug
  • [3] Light bulb banana plug
  • [2] Banana cable
  • [2] Insulated alligator clips
  • [1] Lantern battery

Classroom Assembly

  1. Plug in wires and light bulbs into the board as desired.
  2. Attach alligator-clipped cables to the battery.

Important Notes

  • The clips should protect against shorting the battery, but it doesn't hurt to check this hasn't happened anyway.


  1. Ask students to guess the brightness of each light bulb for a particular configuration of wires and light bulbs.
  2. Plug in the lantern battery.
  3. Unplug the battery.
  4. Change to a different configuration of wires and light bulbs, and repeat steps 1–3.

This demo is very flexible, and many different configurations are possible. The two available circuit boards are of different designs, so make sure to request the one that can do what you want. Here are some suggested arrangements:

  • One bulb disconnected, one bulb connected
  • Two bulbs in parallel
  • One bulb in parallel with two series bulbs
  • One bulb in series with two bulbs in parallel
  • Three bulbs in series


Additional Resources


  • PIRA 5F20.50


  • Don't attempt this at home!

Last revised

  • 2019


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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.