Tuesday, January 17, 2012

AP Physics
Challenge Circuits

Learning Objectives
Students will build several circuits using switches and principles of series and parallel circuitry.

Activity Type
This activity would best be used as an introduction to circuits and electricity. No previous experience in electricity or circuits is required for students to complete these challenges. This activity could also be used as a practicum component to a unit test on circuits and electricity. 

Assignment Details
  • Teams of students will use a variety of simple circuit equipment (batteries, bulbs with holders, wires, alligator clips, and SPDT switches) to complete four circuit challenges. 
  • Circuit Challenges:
    1. String of Lights: Create a string of three lights that could be used for a Christmas Tree. If one of the three lights breaks (or is loosened from its socket) the other lights should still stay on.
    2. Lighting a Tunnel: Designing lights for a tunnel, you would like to be able to control two lights with one switch, which both turns on the light in front of you and turns off the light behind you. Create such a circuit. 
    3. Lighting a Stairwell: In this case we want to control one light with two switches - one at the top and one at the bottom of a stairwell. Wire a circuit with one bulb in which either switch can turn the bulb on or off at any time.
    4. Dimmer Switch: See if you can make a switch that would not only allow you to turn on and off a light, but also control how bright the light bulb gets. Try to create such a circuit. 
  • After a team completes one of the challenges, the team must demonstrate the function of the circuit to the instructor. Then, each student on the team must draw an accurate diagram that would allow them to rebuild the working circuit.

Instructor's Notes
  • The circuit challenges are listed in order of difficulty with the easiest circuit first. It is acceptabe if some of the groups never reach the last two challenges, which are particularly tricky.
  • As you review the student circuits, be sure that they are not using a short in the circuit to make the light go out. Each of these circuits can be built without a short circuit. 
  • Proper understanding of SPDT (single pole double throw) switches is important for completing challenges #2 and #3. The "off" position of the switch must still make an electrical connection in order for students to create these circuits.
  • Students do not necessarily need to know about proper circuit diagrams before making their circuit drawings. In fact, it may be helpful for students to experience the difficulty of drawing a circuit before learning about circuit diagram conventions. 
  • Creating a dimmer switch (challenge #4) will require some way to change the current of the circuit. This could be accomplished by adding more than one bulb, or by adding a potentiometer (adjustable resistance device) to the circuit. 

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