Polarities

The choice of sign for the voltage of terminal A with respect to terminal B establishes a convention by which we can distinguish between energy supplied to an element, and energy that is supplied by the element itself. If positive current is entering terminal A of the load and an external source must expend energy to establish this current, then terminal A is positive with respect to terminal B.

The abbreviation mV stands for millivolt (0.001 V), µV stands for microvolt (0.000001 V), and kV stands for kilovolt (1000 V). The range of values that is encountered in practice is large. We use a voltmeter to measure voltage. Figure 3.2 shows a symbol of voltmeter in an electric circuit.

Figure 3.2 Measuring voltage drop.
               

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