Ex:           In the circuit below, the currents in each element are labeled as shown. Using the passive sign convention, label the potential difference across each element and show its polarity.

 

 

 

Ans:        

                 

                  (Any labeling with current measurement arrows pointing from + signs to - signs of voltage measurements is valid.)

 

Sol'n:      The passive sign convention dictates that the current measurement arrow always points away from the + sign and toward the - sign of the voltage measurement. Note that the current arrow and + and - sign for voltage indicate only the polarity of current and voltage measurements�NOT the direction of the physical flow of current or the sign of the actual voltage. In other words, the arrows and + and - sign tell us how to connect the leads of a multimeter to make a measurement. We do not know, (nor do we have to know), in advance which direction current is flowing or what the actual sign of the voltage will be.