Engineering Board Exam Reviewer · Circuit Theorems in AC Analysis · medium

A source of 60 V 0° drives a branch Z1=20-j60, in series with the parallel branch Z2=-j50, , as shown. Terminals a and b are the open terminals across Z2. What is the maximum average power that can be delivered to a load connected across a-b?

  1. 180 W
  2. 45 W
  3. 6.36 W
  4. 90 W

Answer

B. 45 W

Solution

With the source replaced by a short circuit, ZTh=Z1 Z2=Z1Z2/Z1+Z2=28.3 -81.9°, . VTh=VZ2/Z1+Z2=60 V·-j50, /20-j110, =26.8 -10.3° V. RTh=4, . With ZL=ZTh*, Pmax= |VTh|24RTh= (26.8 V)24(4, )=45 W.

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