# How to determine sign of voltage with a current source in series

1. Current flows in the same direction (or CCW) for both circuit A and B. In respect to ground, circuit B is just a rotation of circuit A along the same path - these two circuits (A and B) should be entirely identical, regardless of the rotation positions of these elements. Why is there a change of sign in voltage (i.e. +12V for B and -12V for A)?

2. Circuit C is a flip of circuit A. Current in A and C flows in the opposite direction - CCW for A, and CW for C. Their signs of voltage should flip as well. Why is that is the simulation I get the same voltage sign (-12V) for both nodes (A and C)?

• A and C are identical circuits .. A and B are not Nov 27, 2020 at 16:39
• Does the arrow point at the top of the resistor or the bottom, in each cct?
– user16324
Nov 27, 2020 at 17:42

Why is there a change of sign in voltage (i.e. +12V for B and -12V for A)?

Not quite. What you should get when you rotated the circuit was this: -

And now, both nodes will have the same polarity voltage.

So, if you actually did reposition the GND node to where you show it in your original picture, the voltage polarity would reverse. But that ain't a simple rotation!

• So whenever the current source arrow points to ground, voltage or current is negative. Is that the proper way to see it?
– KMC
Nov 27, 2020 at 17:34
• Think about the resistor and what voltage it has to have on its upper terminal in your left diagram when 12 amps is being pulled from it. The resistor has to drop 12 volts (of course) and, because the resistor is grounded on the other terminal, the upper terminal has to be at -12 volts to satisfy the implied current direction. Nov 27, 2020 at 17:40
• So whenever the current source arrow points to ground, voltage or current is negative. - not as a rule but, in your circuit yes. I mean; if the resistor's top terminal were fed from a 19 volt DC supply (for example) and the current source dragged 12 amps to ground from the bottom terminal of the resistor, that bottom terminal has to be at +7 volts relative to ground. That's ohm's law. It prevails. Nov 27, 2020 at 17:43