# Homework Help: Effective reisistance of an unbalanced wheatstone bridge.

1. Sep 11, 2007

### Mr Virtual

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

I have an exam and therefore quick help is requested.

I need a simple way to find out the resistance of an unbalanced wheatstone bridge.
Suppos R1=2 ohm, R2=1 ohm, R3=4 ohm, R4=4 ohm and the connecting bridge's R5=10 ohm.
Here, R1/R2 is not equal to R3/R4. Then How to find net resistance.

3. The attempt at a solution

I don't know and can't find any way to attempt such a question, though there must be many. So no idea how to do this.

Help please!!

Mr V

2. Sep 11, 2007

### Staff: Mentor

Usually on problems like this one, you can use KCL to solve for the node voltages (assume 1V across the whole bridge for the calculation). Once you have the node voltages, those give you the currents, which gives you the total current for the 1V excitation, which gives you the resistance.

3. Sep 11, 2007

### Mr Virtual

A little more explanation?

4. Sep 11, 2007

### learningphysics

I agree with berkeman. Use the node voltage method, for the two nodes on either side of R5.

You'll have 2 equations, with two unknowns. Once you have the voltage of those two nodes, you can get the current coming out of the voltage source in terms of V.

Then resistance is just V/I.

5. Sep 13, 2007

### Mr Virtual

Thanks so much!

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