Find the Equivalent Resistance of a Network

  • Thread starter jumbogala
  • Start date
  • #1
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Homework Statement


A network consists of a combination of parallel and series connections. What is the equivalent resistance of the network? (Hint: Use the series and parallel resistance formulas).

The network looks like this:
resistance.jpg



Homework Equations


When a circuit is in series, R = R1 + R2 + R3...

When a circuit is in parallel, R = 1/R1 + 1/R2 + 1/R3...


The Attempt at a Solution


First, c and b are in series, so I just add them up. 5 + 3 = 8.

Now, a, d, and this new resistor of value 8 are in series. So add them up again.
8 + 4 + 1 = 13.

Did I do that correctly?
 
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Answers and Replies

  • #2
LowlyPion
Homework Helper
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Sorry. B and C are ||.

Not in series.
 
  • #3
423
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They look like they're in series to me... how can you tell?

That changes my answer to 1/5 + 1/3 = 0.533. And 1/0.533 = 1.875.

Then 1.875 + 4 + 1 = 6.875
 
  • #4
LowlyPion
Homework Helper
3,090
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They look like they're in series to me... how can you tell?

That changes my answer to 1/5 + 1/3 = 0.533. And 1/0.533 = 1.875.

Then 1.875 + 4 + 1 = 6.875
That looks more like it.
 
  • #5
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When a circuit is in parallel, R = 1/R1 + 1/R2 + 1/R3...
This is wrong. I think you meant to write:
1/Req = 1/R1 + 1/R2 + 1/R3...

They look like they're in series to me... how can you tell?
Notice that the upper terminals of C and B share a common node. Similarly, the bottom terminals of C and B share a common node.
 
  • #6
423
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Yeah, I meant to write 1/Req = 1/R1 + 1/R2...

So a is in series with c because it only shares one common node? And b and c are in parallel because they share two nodes?
 
  • #7
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So a is in series with c because it only shares one common node? And b and c are in parallel because they share two nodes?
Well, a better way to say it is this: A is in series with the combination C||B.

If the same current flows through two resistive elements, the elements are in series.
If the same voltage potential is across two elements, the elements are in parallel.

Does that help?
 
  • #8
423
2
That helps a lot - I understand now. Thank you!
 

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