# Can You Combine Current Sources Question

1. May 21, 2013

### eatsleep

http://imgur.com/09Rj0ND

2. V=IR

3. My real question is if I can combine the current sources. I'm pretty sure you cannot. I have combined the resistors in parallel, but I am not sure what to do next

Last edited by a moderator: May 21, 2013
2. May 21, 2013

### Staff: Mentor

It depends on the situation, but in this case you cannot, IMO. There are current branches off of the top node, and the right side source is a dependent source.

If you have two independent current sources in parallel, you would usually be able to combine them.

3. May 21, 2013

### SammyS

Staff Emeritus
Display of your image.

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4. May 21, 2013

### eatsleep

In order to solve this problem, am I correct in first combining the resistors? Then does Ib turn into 1Amp?

5. May 21, 2013

### Staff: Mentor

Not the way the circuit is drawn. Can you post the original circuit, so we can check that this drawing is correct?

The way it is drawn is a bit confusing. You show a wire carrying a current Ib, but that wire shorts the top of the two resistors, so there is no wire segment that can carry a current...

6. May 21, 2013

### eatsleep

This is the original drawing, from my teacher

7. May 21, 2013

### Staff: Mentor

That's unfortunate.

Well, you can still try to solve it, and hopefully it will yield the correct answer. Write KCL equations for the left node (to the left of the arrow "Ib") and for the right node, first assuming that they are at different voltages. Solve the right side equation to get a relationship between the voltage and the current Ib. Then assume that the two voltages are the same, and solve for the current Ib.

Seems kind of clunky. I honestly do not know why you were given a circuit drawn like that...

8. May 21, 2013

### eatsleep

Thank you for the help!

9. May 21, 2013

### SammyS

Staff Emeritus
Using Kirchhoff's Current Law:
What is the current through the 2kΩ resistor? (in terms of Ib) ?

What is the current through the 5kΩ resistor? (in terms of Ib) ?​

10. May 21, 2013

### eatsleep

2kΩ resistor 10Ib?

5kΩ resistor 8Ib-1?

11. May 21, 2013

### SammyS

Staff Emeritus
Yes.

No.

1 Ampere into the junction. Current of Ib out.

Those together with current through 5kΩ , whichever direction you choose.

12. May 21, 2013

### eatsleep

I'm sorry, so the current through the 5kΩ is Ib-1?

13. May 21, 2013

### SammyS

Staff Emeritus
Yes.

Upward.

14. May 21, 2013

### eatsleep

Will solving for Vr1 by doing 5(Ib-1)=2(10Ib), solving for Ib, then plugging that backing to 5(Ib-1) work? seems too easy

15. May 21, 2013

### SammyS

Staff Emeritus
Yes.

It should be easy to check the results.