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P q
s
Peak icon to the right of the Toggle cursor key). It occurs at the same
point as the maximum current at a level of 50 W. In particular, note that
the power curve shows two cycles, while both vR and iR show only one
cycle. Clearly, the power curve has twice the frequency of the applied
signal. Also note that the power curve is totally above the zero line,
indicating that power is being absorbed by the resistor through the
entire displayed cycle. Further, the peak value of the power curve is
twice the average value of the curve; that is, the peak value of 50 W is
twice the average value of 25 W.
The results of the above simulation can be verified by performing the
longhand calculation using the rms value of the applied voltage. That is,
P � � VR
R
2
� � � (10
V)
4 �
2
� � 25 W
Power Curves: Series R-L-C Circuit The network of Fig. 19.38,
with its combination of elements, will now be used to demonstrate that,
no matter what the physical makeup of the network, the average value
of the power curve established by the product of the applied voltage and
resulting source current is equal to that dissipated by the network. At a
frequency of 1 kHz, the reactance of the 1.273-mH inductor will be 8,
and the reactance of the capacitor will be 4 �, resulting in a lagging
network. An analysis of the network will result in
ZT � 4 ��j4 ��5.657 � �45°
E
with I � �� � �1.768 A ��45°
ZT
and P � I 2 R � (1.768 A) 2 10 V �0°
��
5.657 � �45°
4 ��12.5 W
FIG. 19.38
Using PSpice to examine the power distribution in a series R-L-C circuit.
COMPUTER ANALYSIS ⏐⏐⏐ 877