DEMONSTRATING TRANSIENTS

IT IS customary to discuss the growth of current when a battery is connected to a coil, and the growth of voltage across a capacitor when the capacitor is charged through a resistor, at the stage when students have done some work on d.c. circuits and are about to start a.c. theory. At this elementary stage, they may, or may not, be familiar with waveforms on the oscilloscope. If they can take the oscilloscope in their stride, they might be interested in the following demonstrations. If, on the other hand, they belong to the group which regards the oscilloscope as a box that can produce any desired pattern if the knobs are twiddled long enough, the demonstration will be less convincing. The justification for the demonstration in this case would possibly be that exposing students to similar demonstrations over a long enough period may eventually convince some of them that mere rotation of the knobs is not sufficient: it may also be necessary for the theory to be correct.