# Homework Help: Simple voltage drop / sign convention

1. Jul 2, 2013

### Color_of_Cyan

1. The problem statement, all variables and given/known data

[Broken]

2. Relevant equations

voltage drop, KVL

3. The attempt at a solution

I actually did:

-24V - 4V + 6V

= -22V

but this is wrong.

I know going the other way

Vad: 6V + 8V + 12V

= 26V,

because it is only drop, and plus to minus on drops means they are always positive

But it seems for Vab the real correct way counting the sources was

= 26V

I thought it was different for voltage sources and sign orientation?

So when the drop direction is plus to minus (+ to -), the voltage drop is always positive, for both sources AND given sign convention?

Sorry for asking this now. KCL is much easier.

Veb would be

8V - 6V + 24V

= 10V

Last edited by a moderator: May 6, 2017
2. Jul 3, 2013

### lewando

For the passive components this is true and for the voltage source you have shown, this is true.

Sometimes you will encounter a "negative voltage source" (a voltage drop moving from + to - terminals which is negative). These are thrown at you, occasionally, to see how well you react.

You have a simple math error there, I'm afraid.

The drops encountered moving from e to b clockwise are:

-8V (because the voltage increased resulting in a "negative drop")
-6V (same reason)
+24V (because the voltage dropped by 24V going from a to b)

Summing the drops: -8V -6V +24V = 10 V

3. Jul 3, 2013

### 256bits

V$_{eb}$ = -V$_{be}$
V$_{af}$ = 6v
V$_{fa}$ = -6v