# Homework Help: Kirchoff's Loop Rule

1. May 2, 2006

### willydavidjr

I have a diagram on my website and I also attached it to this message. My question is I am wondering if my equation for this loop rule is correct. I am trying to solve it but I am having a problem about the signs I am getting..

This is my equation for this loop:

$$I_2=I_1+I_3$$

$$6V-2I_3-2I_2=0$$

$$1V-2I_3-I_1=0$$

Do you think the above equations are correct?I used the equations but I get different signs that doesn't match the circuit on the diagram...

This is the site of the circuit: www.geocities.com/willydavidjr/loop.html

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Last edited: May 2, 2006
2. May 2, 2006

### Staff: Mentor

Last equation is +I1. Look at the voltage *increase* through R1 in that direction due to I1.

3. May 3, 2006

### willydavidjr

I see. Do you think berkeman the second equation should be 6V - 2I3 + 2I2=0? What do you think?

4. May 3, 2006

### willydavidjr

I don't think that the third equation should be +I1. Because we will get negative answer for I3 and I1. Meaning they have opposite direction and it shouldn't be!

5. May 3, 2006

### Curious3141

The second equation is fine as you wrote it (why do you think the sign is wrong ?). Just amend the third equation as berkeman suggested.

When taking a loop across a resistance, if going with the labelled flow of current, use the minus sign. If going against the labelled flow of current, use the plus sign.

6. May 3, 2006

### willydavidjr

Berkeman what I get for this three equation just as I amended the 3rd equation are I1= 1 amp, I2= 1 amp and I3= 1 amp. Am I correct? I expected to get a negative value for I1 but I didn't get it. All have positive values. Do you think all flow of currents are correct?

7. May 3, 2006

### Staff: Mentor

How can they all equal 1A when your first equation says I2=I1+I3 ?

When you get the answers, just go back and put them on the original drawing, and see if all the voltages and currents add up.

8. May 3, 2006

### willydavidjr

No I mean 2A for I2. Sorry my fault.

9. May 3, 2006