Summary
With the notable exception of
calculations for power (P), all AC circuit calculations are based on the
same general principles as calculations for DC circuits. The only
significant difference is that fact that AC calculations use complex
quantities while DC calculations use scalar quantities. Ohm's Law,
Kirchhoff's Laws, and even the network theorems learned in DC still hold
true for AC when voltage, current, and impedance are all expressed with
complex numbers. The same troubleshooting strategies applied toward DC
circuits also hold for AC, although AC can certainly be more difficult
to work with due to phase angles which aren't registered by a handheld
multimeter.
Power is another subject altogether, and
will be covered in its own chapter in this book. Because power in a
reactive circuit is both absorbed and released -- not just dissipated as
it is with resistors -- its mathematical handling requires a more direct
application of trigonometry to solve.
When faced with analyzing an AC circuit,
the first step in analysis is to convert all resistor, inductor, and
capacitor component values into impedances (Z), based on the frequency
of the power source. After that, proceed with the same steps and
strategies learned for analyzing DC circuits, using the "new" form of
Ohm's Law: E=IZ ; I=E/Z ; and Z=E/I
Remember that only the calculated figures
expressed in polar form apply directly to empirical measurements of
voltage and current. Rectangular notation is merely a useful tool for us
to add and subtract complex quantities together. Polar notation, where
the magnitude (length of vector) directly relates to the magnitude of
the voltage or current measured, and the angle directly relates to the
phase shift in degrees, is the most practical way to express complex
quantities for circuit analysis.
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