Figure 2.10: Vector magnitudes add like scalars for a common angle.
Similarly, if AC voltage sources with the same phase angle are connected together in series, their
voltages add just as you might expect with DC batteries: (Figure 2.11)
Please note the (+) and (-) polarity marks next to the leads of the two AC sources. Even though
we know AC doesn’t have “polarity” in the same sense that DC does, these marks are essential to
knowing how to reference the given phase angles of the voltages. This will become more apparent
in the next example.
If vectors directly opposing each other (180o out of phase) are added together, their magnitudes
(lengths) subtract just like positive and negative scalar quantities subtract when added: (Figure 2.12)
Similarly, if opposing AC voltage sources are connected in series, their voltages subtract as you
might expect with DC batteries connected in an opposing fashion: (Figure 2.13)
Determining whether or not these voltage sources are opposing each other requires an examination
of their polarity markings and their phase angles. Notice how the polarity markings in the