Network Theorems
(AC Circuits)
 D C Kulshreshtha
Maximum Power Transfer Theorem
for AC Circuits
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The power delivered to the load is
Phasor current and voltage are
where
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A little forethought saves us some work. (XTh +
XL) absorbs no power; any nonzero value only
reduces PL. Hence we can put XL = - XTh, so as
to get
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This expression, we have already maximized for
purely resistive case, by selecting RL = RTh.
Hence, we must have
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Exercise
Show that if the load is purely resistive in an
ac circuit, the condition for maximum power
transfer is
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