# Simple circuit question

• Engineering

## Homework Statement

I'm going to try drawing the circuit. Numbers are added to it for reference. I apologize for the formatting. I'm not sure how to do white space. Edit: for VB the + is on top.

VA and VB are switches.

I need to figure out the voltage across VA and VBB when they are:
1. open, open
2. open, closed
3. closed, open
4. closed, closed

1-------(+ VA -)-------(+ 8 V -)-------2--------------3
|_______________________________|___________|
12Ω____________________________15Ω_______(+ VB -)
|_______________________________|___________|
6-----------------------------------------5--------------4

V = IR
Kirchhoff's Laws

## The Attempt at a Solution

1. When they are both open there isn't a circuit. So, VA = 0 V and VB = 0 V.
2. Again, no circuit.
3. There is a circuit. It has a total resistance of 27 Ω (I don't know if this matters). VA = -8 V and VB = 0 V.
4. I'm not sure about this one. There are two loops, but loop 1256 has a total resistance of 27 Ω and loop 1346 has a total resistance of 12 Ω. So 1256 gets 27/39 = 9/13 of the current and voltage and 1346 gets 12/39 = 4/13 of the current and voltage? So VA = -8*9/13 V and VB = -8*4/13 V?

Last edited:

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NascentOxygen
Staff Emeritus
1. When they are both open there isn't a circuit. So, VA = 0 V and VB = 0 V.
Circuit or no circuit, does not give the answer. If a voltmeter (or any device) were to be connected between the 2 terminals of the switch in question, would that form a path for current to flow through the meter? If so, what voltage would it register? That's the question you must address.

NascentOxygen
Staff Emeritus
Code:
If you wish to construct ASCII diagrams, enclose those lines
between [b][[/b][b]code][/b] and [b][/code[/b][b]][/b] statements to display in a
fixed-width font.

CWatters