Download Problem 3.3 Use nodal analysis to determine the current Ix and

Problem 3.3 Use nodal analysis to determine the current Ix and amount of power
supplied by the voltage source in the circuit of Fig. P3.3.
I
V
Ix
9A
2Ω
8Ω
+
_ 40 V
4Ω
Figure P3.3: Circuit for Problem 3.3.
Solution: At node V , application of KCL gives
V V V − 40
=0
−9 + + +
2 4
8
1 1 1
40
V
= 9+
+ +
2 4 8
8
7V
= 9+5
8
V = 16 V.
The current Ix is then given by
Ix =
V
16
=
= 4 A.
4
4
To find the power supplied by the 40-V source, we need to first find the current I
flowing into its positive terminal,
I=
V − 40 16 − 40
=
= −3 A.
8
8
Hence,
P = V I = 40 × (−3) = −120 W
(The minus sign confirms that the voltage source is a supplier of power.)
c
All rights reserved. Do not reproduce or distribute. 2013
National Technology and Science Press