Due to the simplicity of the circuit, this apparatus is not sensitive to current surges or miss-set knife switches. We generally complete the parallel calculation in class before using the apparatus. After the currents and voltages are determined, the students are requested to set the system up in the parallel configuration, and to show that everything goes as expected. Next the students are requested to predict the behavior of the circuit in series. They set up the circuit and test to see the outcome.
Many students predict behavior inconsistent with actual performance.
After a simple circuit analysis, the actual performance is easily understood. This apparatus is useful in concluding the concepts of simple parallel and series circuit analysis. Its simplicity and use of everyday components seem to be appreciated by students. The actual wattage used by the lamps in the series configuration are numerically different from the calculations due to the variance of resistance with temperature in a normal incandescent lamp, but the qualitative nature is very illustrative. Additionally, discussions about the temperature dependence can be used to compare and contrast the idealization of theory and the real behavior of circuit elements.