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202 ⏐⏐⏐ PARALLEL CIRCUITS
The result is Fig. 6.65 which clearly reveals that the voltage is the
same across all the parallel elements and the current increases significantly
with decrease in resistance. The range in resistor values suggests,
by inspection, that the total resistance will be just less than the smallest
resistance of 22 �. Using Ohm’s law and the source current of 2.204 A
results in a total resistance of R T � E/I s � 48 V/2.204 A � 21.78 �,
confirming the above conclusion.
Electronics Workbench
Parallel dc Network For comparison purposes the parallel network
of Fig. 6.65 will now be analyzed using Electronics Workbench. The
source and ground are selected and placed as shown in Fig. 6.66 using
the procedure defined in the previous chapters. For the resistors,
VIRTUAL – RESISTOR is chosen, but it must be rotated 90° to match
the configuration of Fig. 6.65. You can accomplish this by first clicking
on the resistor symbol to place it in the active state. Be sure that the
resulting small black squares surround the symbol, label, and value;
otherwise, you may have activated only the label or value. Then rightclick
the mouse. The 90 Clockwise can then be selected, and the resistor
will be turned automatically. Unfortunately, there is no continuum
here, so the next resistor will have to be turned using the same procedure.
The values of each resistor are set by double-clicking on the resistor
symbol to obtain the Virtual Resistor dialog box. Remember that
the unit of measurement is controlled by the scrolls at the right of the
unit of measurement. For EWB, unlike PSpice, megohm uses capital M
and milliohm uses lowercase m.
FIG. 6.66
Using the indicators of Electronics Workbench to display the currents of a
parallel dc network.
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