Introductory Physics Volume Two

126 Time Varying Fields 6.8
voltage as an example. The fact that the inductor voltage is one quarter
of a cycle ahead of the current, means that the inductor voltage
phasor is 90 ◦ ahead of the current phasor.
If you imagine the phasors rotating you can see that the projection of
the voltage, onto the horizontal axis, will reach a peak one quarter of
a cycle before the projection of the current reaches its peak.
Here is the phasor diagram for a capacitor.
At this point the phasor diagram has only allowed us to represent
what we already know. The phasor diagram is far more useful. For
example the phasor diagram will alow us to use Kirchhoffs loop rule
for AC circuits, as we will see in the following example. The idea of a
phasor is useful in many areas of physics and engineering. We will see
more examples in the next chapter.
Example
Suppose that we have a capacitor and a resistor in series. What is the
effective impedance of the combination. First imagine that we connect
the combination to an AC source.
+
+
V S–
C
R
+
V R
–
V C
–