KVL Node Voltage: Positive vs Negative Assumption in Homework Solution

[cpatel23]

Homework Statement

Homework Equations

ƩCurrent(in) = ƩCurrent(out)

The Attempt at a Solution

----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)

 

[gneill]

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.