Equivalent resistance question

In summary, the conversation discusses calculating the effective resistance between points A and F in a circuit with multiple resistors. Initially, there is confusion about whether the first resistance should be ignored and the current takes the lower path or if all three resistors are in parallel. It is eventually determined that the correct approach is to redraw the circuit, realizing that certain points are at the same potential, and that each resistor is in parallel with each other.
  • #1
niktoo1
2
0
(please check attachment)
Calculate the effective resistance between A and F

Initially, I thought that the first resistance is ignored and the current takes the lower path. Then 2Ω and 2Ω are in parallel giving an effective resistance of 1Ω.

However, it could also be that all three are in parallel and thus give an effective resistance of 2/3 Ω.
If the upper and lower loops are ignored, the resistance is 6Ω!
What is the correct answer??
 

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  • #2
hi niktoo1! welcome to pf! :smile:
niktoo1 said:
Initially, I thought that the first resistance is ignored and the current takes the lower path.

hint: wouldn't that only be if the current through BC and CD was flowing the same way? :wink:
However, it could also be that all three are in parallel and thus give an effective resistance of 2/3 Ω.
If the upper and lower loops are ignored, the resistance is 6Ω!

hint: if two points are shown joined by a zero-resistance wire, then they must be at the same potential

so you can re-draw the diagram omitting the wire completely, and showing those two points as the same point :wink:
 
  • #3
Don't ignore anything. Redraw realizing that A, B, and D are the same node and C, E, and F are also the same.
 
  • #4
attachment.php?attachmentid=65681&stc=1&d=1389875734.jpg
 

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  • #5
tiny-tim said:
so you can re-draw the diagram omitting the wire completely, and showing those two points as the same point :wink:


Does that mean that each resistor is in parallel with each other?
 
  • #6
niktoo1 said:
Does that mean that each resistor is in parallel with each other?

what diagram do you get? (mark it with A BD and CE as in the original diagram)
 
  • #7
niktoo1 said:
Does that mean that each resistor is in parallel with each other?

Which part of post #4 did you not understand?
 

Related to Equivalent resistance question

1. What is equivalent resistance?

Equivalent resistance refers to the total resistance of a circuit or network, which is calculated by combining individual resistances in a specific way.

2. How is equivalent resistance calculated?

Equivalent resistance is calculated by using Ohm's law, which states that resistance is equal to voltage divided by current. In series circuits, equivalent resistance is the sum of all individual resistances, while in parallel circuits, the reciprocal of equivalent resistance is equal to the sum of the reciprocals of individual resistances.

3. Why is finding equivalent resistance important?

Finding equivalent resistance is important in analyzing and designing circuits, as it helps determine the overall behavior and performance of the circuit. It also simplifies the circuit, making it easier to calculate other parameters such as current and voltage.

4. What is the difference between series and parallel circuits?

Series circuits have all components connected in a single loop, while parallel circuits have multiple branches where each component has its own separate path. In series circuits, the same current flows through each component, while in parallel circuits, the voltage is the same across each branch.

5. Can equivalent resistance ever be greater than the individual resistances?

No, equivalent resistance can never be greater than the individual resistances in a circuit. This is because adding more resistors in series increases the overall resistance, while adding more resistors in parallel decreases the overall resistance.

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