Simplifying Complex Resistor Circuits

[jey1234]

Simplifying "Complex" Resistor Circuits

Homework Statement

Question 1:

I have an E&M test coming up and I'm having trouble simplifying complex circuits. Our teacher told us something about "pinching" the wires which I didn't really understand. I found the following link "http://www.allaboutcircuits.com/vol_1/chpt_7/3.html". I got the right solution for the homework problem using it but is this method reliable? Does it always work? Are there any other suggestions for tackling this type of problems?

Question 2

The attached problem is from homework. The question is what would an ohmmeter read between a and b. I don't understand these questions much. I simplified it to what is shown in the second attached image without much trouble. Now my intuition tells me that I should add these three remaining resistors (in series) and that's the answer (40.3 Ω) but that's apparently wrong. My teacher says that I should add the 7 Ω and 23.3 Ω together (in series). Then take the resulting 30.3 Ω resistor and add it with the 10 Ω (in parallel) and that gives 7.5 Ω, which is the correct answer. Can someone explain this to me please?

Please excuse the weird looking lines in the diagrams. I'm new to Visio. Thanks.

Homework Equations

The Attempt at a Solution

Attached.

 

[phinds]

Relative to points a and b, what is the parallel/series configuration? Don't get hung up on the particular way you have DRAWN them ... that is irrelevant. Follow the wires.

 

[jey1234]

Relative to points a and b, what is the parallel/series configuration? Don't get hung up on the particular way you have DRAWN them ... that is irrelevant. Follow the wires.

Could you please elaborate? Thanks.

 

[phinds]

Not really. Redraw the circuit based on points a and b, not on some arbtrary configuration and maybe you'll see it.

 

[SammyS]

Homework Statement

Question 1:

I have an E&M test coming up and I'm having trouble simplifying complex circuits. Our teacher told us something about "pinching" the wires which I didn't really understand. I found the following link "http://www.allaboutcircuits.com/vol_1/chpt_7/3.html". I got the right solution for the homework problem using it but is this method reliable? Does it always work? Are there any other suggestions for tackling this type of problems?

Question 2

The attached problem is from homework. The question is what would an ohmmeter read between a and b. I don't understand these questions much. I simplified it to what is shown in the second attached image without much trouble. Now my intuition tells me that I should add these three remaining resistors (in series) and that's the answer (40.3 Ω) but that's apparently wrong. My teacher says that I should add the 7 Ω and 23.3 Ω together (in series). Then take the resulting 30.3 Ω resistor and add it with the 10 Ω (in parallel) and that gives 7.5 Ω, which is the correct answer. Can someone explain this to me please?

Please excuse the weird looking lines in the diagrams. I'm new to Visio. Thanks.

Homework Equations

The Attempt at a Solution

 

Connect a battery across a & b. Now, what is the series/parallel combination for the resistors?

 

[jey1234]

Thank you guys. I think I understand it better now after doing many similar problems. I just "followed the wires" :)