1. Feb 6, 2008

### BuBbLeS01

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

What is the resistance R? (R1=15.13 Ω, I1=2.77 mA , I2=1.81 mA. Give answer in Ω.)
What is the emf of the battery?

2. Relevant equations

I = E/R

3. The attempt at a solution

How do I solve this with the batteries EMF?

2. Feb 6, 2008

### Staff: Mentor

Write 2 equations with the two unknowns (V and R), then solve for both.

And shrink that picture!

3. Feb 6, 2008

### BuBbLeS01

Ok let me see what I can come up with...
How do you shrink it? I did it on tinypic.com

4. Feb 6, 2008

### BuBbLeS01

E = -v1 - V2
E = Ir1 + Ir2
R = E/i

5. Feb 6, 2008

### Staff: Mentor

With Paint or other figure manipulation/drawing programs, you can choose to "Save As" and specify the resolution.

6. Feb 6, 2008

### BuBbLeS01

Are those the right equations? I am not seeing how to solve this?

7. Feb 6, 2008

### Staff: Mentor

Write one equation for the current and voltage in the middle branch, and one equation for the current and voltage in the right branch.

8. Feb 6, 2008

### BuBbLeS01

MIDDLE BRANCH:
R = E/I

RIGHT BRANCH:
R = E/I1 + I2

That doesn't look right??

9. Feb 6, 2008

### Staff: Mentor

Why are you not using the names of the resistors in the figure? There are two resistors in the right branch, correct? And current J1 flows in the left branch, and J2 flows in the right branch. Both branches have the same voltage across them, correct?

Take your time and think it out. I need to bail -- you'll get it (or more help may stop by if you have more questions).

10. Feb 6, 2008

### BuBbLeS01

MIDDLE BRANCH:
R = E/I1

RIGHT BRANCH:
R + R1= E/I2

Is that right?

11. Feb 6, 2008

### BuBbLeS01

Ok so I think I got it...I just set them equal to eachother and I get...
I1 * R = (R + R1) * I2
But for some reason I don't know how to solve for R!! I can't figure it out...very sad...please help me! I have tried all sorts of things and I am not getting anywhere...

12. Feb 6, 2008

### BuBbLeS01

can anyone help me with this part?

13. Feb 6, 2008

### rl.bhat

I1 * R = (R + R1) * I2
Substitute the values of I1, I2 and R1 and solve for R

14. Feb 6, 2008

### BuBbLeS01

Thats what I am trying to do but I can't figure out how to get the R by itself on one side since there are 2 of them. I always end up with R/R which is just 1. Its not making sense to me.

15. Feb 7, 2008

### dingpud

Do you already know what the answer is suppose to be? We use to get the solution to some of our problems, but had to show the work in getting to it.

Do you end up with R*(2.77) = R*(1.81) + (27.39) ?

16. Feb 7, 2008

### BuBbLeS01

No I don't know what the answer should be

17. Feb 7, 2008

### Staff: Mentor

It's simple algebra. Distribute I2 on the right side into the parenthesis. That gives you one R term on the left and one R term on the right, with the additional R1*I2 term on the right. Just move the R term from the right side to the left (you do know how to do that, right?), and then finish solving for R all by itself.