Find Resistance Between A and B

[mmmboh]

Homework Statement

I have to find the input resistance; the resistance between A and B. I think it's Thevinin's theroem, however it is already an open circuit and there are no voltage sources and I can't combine the resistors to make an equivalent. So what do I doEdit: Am I suppose to remove the 4 ohm resistor connecting the two parallels, and find the equivalent resistance of those two and then add back the 4 as if it were in series?...so the final answer is 16/3 ohm? or is that wrong?

 

[JaWiB]

Have you heard of a Y-Delta transform?

 

[mmmboh]

No I don't believe so.

 

[vela]

Place a voltage source across A-B and calculate the current that it would supply. The equivalent resistance will be the voltage divided by the current.

 

[mathman44]

Ok, I tried it like you suggested vela. Made 3 Kirchhoff loops, put in an imaginary voltage source 10V, calculated the current to be 3.5A, so R should be 10/3.5...

 

[vela]

That's the same answer I got.

 

[mathman44]

Sweet, thanks!

 

[mmmboh]

I tried doing the loop thing, I don't think I did it right. Can you explain it please?

 

[ideasrule]

What loop thing? You won't get the answer with Kirchoff's laws alone. Instead, use Thevinin's theorem, pretending that there's a voltage V between A and B.

 

[vela]

It would be better if you explain what you tried, so we can identify where you're having trouble. It's kind of hard to boil all of circuit analysis down to a forum post.

 

[mmmboh]

Never mind I think I got it. I1=7A/2, R=10V/3.5A.