Why does my professor's node voltage have opposite sign from the textbook?

Join the discussion
Registration is free. Start your own thread to ask a follow-up.
Sign up Log in
1 reply · 2K views · last reply
cpatel23
Messages
16
Reaction score
0

Homework Statement



Handwritten circuit diagram with nodes a, b and c, a 4V source, 6 ohm and 12 ohm resistors, currents I, I2 and I3, and a 2A current source; answers Va = -4V, Vb = 6V, Vc = -2V shown at right.


Homework Equations



ƩCurrent(in) = ƩCurrent(out)

The Attempt at a Solution


Handwritten node voltage analysis on lined paper: KCL equation with Vb, Vc and 2 and 4 amp sources, boxed results Vb = 4 V, Vc = 10 V, Va = 4 V, I1 = -1, I2 = .833, I3 = .166, and a KVL check.
----In situations like that, my book takes the node to be a positive voltage when the voltage source is connected like above. For some reason my professor takes it to be negative, is this why my answer is different?


(sorry for the big pictures)
 
Last edited:
Physics news on Phys.org

Discussion

The potential at node a with respect to the reference node depends entirely upon the polarity of the 4V source. The picture is a bit fuzzy around that source, but it appears that the "+/-" indicator shows "+" at the top. That would make node a +4V. It would also make the indicated answers incorrect.

If the 4V source polarity were reversed, then node a would be at potential -4V with respect to ground, and the given answers would then look good.
 

Similar threads

Why does radial acceleration have opposite sign to centripetal acceleration?
  • JustSomeGuy80
  • · Replies 1 ·
  • Introductory Physics Homework Help
Replies
1