Discussion in 'Homework Help' started by Rock33y, May 21, 2008.

1. ### Rock33y Thread Starter New Member

May 21, 2008
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How do you find the equivalent resistance of a circuit?

2. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
By reducing series and parallel combinations down to a single resistance between a pair of nodes.

3. ### Rock33y Thread Starter New Member

May 21, 2008
4
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sorry don't really get your explanation.. I was trying to solve this:

A 7 ohm, a 1 ohm, and a 10 ohm resistor are in series. This series combination is then in parallel with a 6 ohm resistor. The combination of four resistors is then in series with a 10.3 ohm resistor. A 20 V battery is used. What is the equivalent resistance?

If you can explain the above question, it'll be much appreciated

Apr 15, 2008
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5. ### Rock33y Thread Starter New Member

May 21, 2008
4
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okay so im using this:

what operation do you use with the R1 and R2.. (aside from the addition one).

6. ### mik3 Senior Member

Feb 4, 2008
4,846
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On the numerator you multiply R1 by R2

7. ### hgmjr Moderator

Jan 28, 2005
9,030
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You can also read the material on series and parallel circuits here in the AAC ebook.

hgmjr

8. ### Caveman Active Member

Apr 15, 2008
471
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Is this an algebra question? You just substitued R1, R2, and R3 into the equation and get Req.

9. ### Rock33y Thread Starter New Member

May 21, 2008
4
0
thanks for all the help.. the answer is suppose to be 14.8 ohm..

10. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,387
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Show your work and then someone can tell you where you went astray.

11. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
I prefer to answer your PM in the open forum so others may benefit.

Your explanation of the question was just fine. I don't know how much plainer my answer could have been. In the thread above there is a relationship for two resistors in parallel. This relationship can be applied recursively to any number of resistors in parallel. There is also the following relation
Code ( (Unknown Language)):
1.
2. For n resistors in parallel R1, R2, ..., Rn.
3. The total resistance Rt, is given by
4.
5. 1/Rt = 1/R1 + 1/R2 + ... + 1/Rn
6.
If you really want to impress your friends at cocktail parties you can refer to this as adding conductances measured in mho which is ohm spelled backwards.

Another fun factoid is that in any parallel combination the total resistance is always strictly less than the smallest resistance on any branch.