Chapter 12
Phasors
Typical MCQ’s
•
Given the circuit diagram, determine the voltages, currents, and their ratios at the
given frequency and at varied frequencies
•
Given the circuit diagram, calculate the voltages and currents using voltage and
current division, as well as node voltage and mesh current methods
Concepts & Strategies
•
Under certain conditions (see below), you can use a generalized form of Ohm’s
law
V=I
⋅
Z
where the voltage
V
and current
I
are phasors (complex numbers
that carry information about both the magnitude and phase shift of sine waves)
and
Z
is the impedance – a complex equivalent of resistance (see below)
•
The conditions are:
1.
All sources in the circuit should be sinusoidal, at the same frequency
ω
2.
All circuit elements should be linear
3.
The circuit should be in a sinusoidal steady state (all transients already
vanished).
•
In general, the impedance
Z
is a complex number, which means that voltage
V
and current
I
may have different phase angles.
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 Spring '07
 Ganago
 Alternating Current, Frequency, Volt, Electrical impedance, A. Ganago

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