Problem # 4.79
The variable resistor in the circuit shown is adjusted for maximum power transfer
to R0.
a) Find the value of R0.
b) Find the maximum power that can be delivered to R0.
c) Find a resistor in Appendix H closest to the value in part (a). How much
power is delivered to this resistor?
Remove R0 and find the Thevenin equivalent circuit.
v  12 v  10 v

 12.5k  0
12k
20k
v  7.03125V
10k
(7.03125V )  5.625V
12.5k
VTh  v  10V  4.375V
v10k 
Determine RTh.
RTh
RTh  [(8k  4k ) (20k )  2.5k ] 10k
RTh  [7.5k  2.5k ] 10k
RTh  5k
R0  RTh  5k
The maximum power that can be delivered to R0 is
2
pmax
pmax
 4.375V 

 5k
10
k



 957 W
The resistor closest to 5kΩ is 4.7kΩ.
4.7 k
(4.375V )  2.12V
4 .7 k  5 k
(2.12) 2

 956.12 W
4.7k
v4.7 k 
p 4 .7 k