Introduction:

DC circuits are so called not because the voltage across each circuit element is constant in time, but because the polarity of the voltages does not change. Current travels in only one direction. We will first test two circuits for which the voltages are stationary in time, and therefore may be measured with a DMM (digital multimeter). The last circuit involves time varying voltages and therefore requires a different sort of instrument for capturing the voltages as a function of time: an oscilloscope. We will return to the oscilloscope presently.

The first two circuits each have a name because they are used so often in practical circuits: the voltage divider and the Wheatstone bridge.