About This Lesson
This activity models a railway track-circuit signalling system. Train wheels and axles provide an electrical connection between the two rails on which they travel. This enables a track signalling circuit to detect the presence of a train on a given section of track.
Students use their existing knowledge of resistors combining in parallel, and of internal resistance, to explain its operation.
This activity is a nice application of what they have learned (resistors combining in a parallel and internal resistance) to a real life situation.