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692 ⏐⏐⏐ SERIES AND PARALLEL ac CIRCUITS
FIG. 15.111
A plot of the steady-state response (t � 3 ms) for v L, v s, and i for the circuit of Fig. 15.109.
dialog box. Finally, since we know that the waveforms are fairly steady
after 3 ms, let us cut away the waveforms before 3 ms with Plot-Axis
Settings-X axis-User Defined-3ms to 5ms-OK to obtain the two
cycles of Fig. 15.111. Now you can clearly see that the peak value of
the voltage across the coil is 100 V to match the analysis of Fig. 15.35.
It is also clear that the applied voltage leads the input current by an
angle that can be determined using the cursors. First activate the cursor
option by selecting the cursor key (a red plot through the origin) in the
second toolbar down from the menu bar. Then select V(Vs:+) at the
bottom left of the screen with a left click of the mouse, and set it at that
point where the applied voltage passes through the horizontal axis with
a positive slope. The result is A1 � 4 ms at �4.243 mV � 0 V. Then
select I(R) at the bottom left of the screen with a right click of the
mouse, and place it at the point where the current waveform passes
through the horizontal axis with a positive slope. The result is A2 �
4.15 ms at �55.15 mA � 0.55 A � 0 A (compared to a peak value of
14.14 A). At the bottom of the Probe Cursor dialog box, the time difference
is 147.24 ms.
Now set up the ratio
147.24 ms
��
1000 ms
�
v
� 360°
v � 52.99°
The phase angle by which the applied voltage leads the source is 52.99°
which is very close to the theoretical solution of 53.13° obtained in Fig.
15.39. Increasing the number of data points for the plot would have
increased the accuracy level and brought the results closer to 53.13°.
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