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Parallel and Series Resistor Simplification HELP

  • Thread starter nlm
  • Start date
  • #1
nlm
3
0
Hi,

I need to simplify this circuit of resistors.

Homework Statement



Image of problem:
http://img24.imageshack.us/img24/9206/resistor1.jpg [Broken]

The Resistor equivalent is 9 ohms, and the solution for R is actually 15 ohms. However, I'm not sure how to get this answer. I think I am getting stuck at the point in my solution on step 4/5 where I seem to have 3 resistors connected to 1 node, but the circuit looks confusing.

I attempted to simplify the resistors in step 5 as resistors in parallel, but I don't think I am getting the right answer.

Homework Equations


parallel = 1/Rtotal = 1/R1 + 1/R2 + 1/R3
Series = Rtotal = R1 + R2 + R3


The Attempt at a Solution



Image of my solution:
http://img24.imageshack.us/img24/4978/resistor2.jpg [Broken]

Any help would be appreciated.
 
Last edited by a moderator:

Answers and Replies

  • #2
Redbelly98
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
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Sorry about the delayed response! :redface:

In step 4, there is an extra line that shouldn't be there. Erase the vertical line segment that is directly to the left of the Rp combination

http://img24.imageshack.us/img24/9206/resistor1.jpg [Broken]

http://img24.imageshack.us/img24/4978/resistor2.jpg [Broken]
 
Last edited by a moderator:
  • #3
4
0
Somewhere along the line (I prefer the beginning) you need to notice the 30ohm resistor is shorted and has nothing to do with your circuit. Visually, using your step 3, you can imagine the current exiting the 5Ohm taking the path of least resistance (the short circuit wire) and flowing through the 3 parallel resistors strands.

This type of problem is readily verifiable with SPICE, Multisim, similar EDA tools - where you can examine the current through each resistor.
 

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