I'm a little confused about why when you find the voltage across a resistor using nodal voltage and superposition, you get two different answers, unless I'm doing it wrong. Configure three 5 ohm resistors in a T configuration, and then two voltage sources on the right and left side of the T configuration, 10V and 30 V.

With nodal analysis: I1(Left branch) + I2(Right branch) = I3(Middle Branch)

When solving for the node voltage I get 40 V.

Using superposition, I get 13.33V

13.33V is the correct answer, but why am I getting 40V as the nodal voltage (i.e. voltage across the resistor on the middle branch?)

10/26/2006 10:11:20 PM

Sum the currents leaving the node at V1

(V1 - 30V)/5 + (V1 - 10V)/5 + V1/5 = 0

Multiply by 5

V1 - 30V + V1 - 10V + V1 = 0

This becomes 3V1 = 40

V1 = 40/3

V1 = 13.33V

10/27/2006 12:49:09 AM

Yep, I found the mistake.

Current through the middle branch is (0 - V1)/5 not V1/5.

Thanks.

10/27/2006 10:48:21 AM