Circuit Paradoxes


Simple paradoxical circuits to encourage thought and discussion about DC circuits.


Two battery-operated circuit paradox demonstrations.





The circuits shown above are connected as shown with the switch for each open. What will happen when the switch is closed? Let students discuss each case before actually doing the experiment. ◙(Left) With the switch open the two lights on the right are equally bright and the light in the middle is off. Q: What happens to the three lights when the switch is flipped? A: Nothing. The potential is the same at the two points connected by the switch. ◙(Right) A third battery is connected into the circuit when the switch is closed. Before the switch is closed both lights are equal in intensity. Q: Wh


C. Frank Griffin and Peter N. Henriksen, Physics challenges, TPT 18, 135-136 (1980). ◙R. Cohen, B. Eylon, and U. Ganiel, Potential difference and current in simple electric circuits: A study of students' concepts, AJP 51, 407-412 (1983). ◙Lillian Christie McDermott, Millikan Lecture 1990: What we teach and what is learned - Closing the gap, AJP 59, 301-315 (1991).