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Mystery Circuit Box Activity
Presenter: Tony Wayne,, Albemarle High School    

Va. SOL:

PH.3 The student will investigate and demonstrate an understanding of the nature of science, scientific reasoning and logic.

PH.11 The student will investigate and understand how to diagram, construct, and analyze basic electrical circuits and explain the function of various circuit components. Key concepts include:
a) Ohm’s law;           b) series, parallel, and combined circuits

National Standards:


Student create a tool to be used to investigate simple, mystery, circuits.


  • A string of 20 Christmas light bulbs that plug into a 120 V outlet
  • A string of 50 or 100 Christmas light bulbs that plus into a 120 V outlet.
  • 7 or more small jewelry boxes or 35 mm film canisters, or something similar that is light tight. You could use toilet paper tubes with the ends closed off.
  • 1 “N” size alkaline battery
  • 2 “AA,” alkaline, batteries. (At least 2 per student group.)

Safety Considerations

         Warn student what a short is how quickly the wire gets hot enough to burn. Also describe to the students that if it gets hot, LET GO! It amazes me how many students want to hold on to a hot wire.


Before doing this activity, I like to do an introductory activity similar to

In a previous activity student divided light bulb up based up brightness and learned about what a diode does to the current in a circuit. They are again provided with those same pieces but it is up to the student to choose what they want. Below are the suggested contents for the boxes.


Description: box2

Example Box

Description: Newsletter Article Spring 2011

When the box/container is closed, tape is closed to keep prying eyes out. Make sure stripped wires are poking out of the box. Tie knots in the wires outside of the boxes to keep the wires from receding back into the box.

How the physics is demonstrated

The specifics depend on which mystery box the student chooses. It is as much logic problem as anything else. What a student should do is to come up with a series of tests and carry them out to figure out what is in each mystery box.

Construction and Tips Regarding the Demonstration

I use Christmas lights because they are cheaper than the typical “long” and “short” bulbs that are used with the CASTLE method of teaching electricity. The two strings of bulbs use bulb with different resistances.

Description: VIP Newsletter 2011 PIC2

The testing circuit can The extra battery will make it easier to see changes in the brightness of the light bulb,

To test for a diode, use a battery, a diode and bright bulb. The bright bulb is used so if it burns dimly, it can still be seen. Touch the test circuit to the leads of the mystery box and then reverse the lead. If there is a diode in the circuit, the test will light up in one direction and not in the other direction. The box with the battery will look very similar to the one with a light and diode. But the brightness will be brighter.

Sometimes I make this box the challenge box and not part of the typical discovery process because of its trickiness.

Sources & References


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