# Measuring voltage between two points

I Have the following Schematic:

The book i am using ask for $V_{BC}$ which I found by $V(B) - V(C) = 0V - 9V = -9V$

The book gives the answer as 9V, is it safe to assume that since voltage is similar to pressure, we cant have negative pressure so I can take the modulus of my result and it would be equal to the 9V would this be allowed ?

• Voltage is only a little similar to pressure. You need to understand what it is, including how does voltage behave with conductors, voltage sources and isolators.
– user76844
Oct 17, 2016 at 17:48
• Use V(final) - V(initial), in this case V(C) - V(B). It is very common to make sign mistakes when doing circuit analysis. Be careful. Oct 17, 2016 at 17:49
• @EugeneSh., then why do we call the base-emitter voltage of an BJT $v_{be}$ instead of $v_{eb}$? I've always seen the convention that $v_{ab} = v_a - v_b$. I think OP's book just has a typo or error in its solution. Oct 17, 2016 at 18:04
• @ThePhoton Hm. Looks like you are right and I am too rusty at this theory... Oct 17, 2016 at 18:06
• The convention definitely is $V_{AB}=V_A-V_B$, and the book is wrong. Oct 17, 2016 at 18:27