Electrical circuit porblem using ohms law

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Discussion Overview

The discussion revolves around a homework problem requiring participants to create an electrical circuit using specific resistors (2 x 12 ohms, 2 x 24 ohms, and 2 x 36 ohms) to achieve a total resistance of 4 ohms. The focus is on exploring circuit configurations and applying Ohm's law to find a solution.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant notes the complexity of the problem due to the requirement to use all resistors and suggests that combining many in parallel is necessary to achieve a total resistance below the values of the individual resistors.
  • Another participant mentions that the resistors being multiples of 4 could be relevant to the target resistance.
  • A different participant shares an attempt that resulted in a resistance of 3.9560Ω, indicating that they were close to the target but did not reach exactly 4.0Ω.
  • One participant proposes the idea of short-circuiting unwanted resistors as a potential strategy, though acknowledges this is generally not acceptable in the context of the problem.
  • Another participant expresses frustration at not being able to find a solution despite trying various combinations of series and parallel configurations.

Areas of Agreement / Disagreement

Participants generally agree on the difficulty of the problem and the need to use all resistors, but there is no consensus on a definitive solution or method to achieve the target resistance. Multiple approaches and configurations are discussed without resolution.

Contextual Notes

Participants express uncertainty about the effectiveness of their attempts and the potential for combinations of resistors, indicating that the problem may involve complex interactions between series and parallel arrangements. There is also mention of rounding in the context of achieving the target resistance.

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Homework Statement


Using all the following resistors : 2 x 12 ohms , 2 x 24 ohms , and 2 x 36 ohms. create a circuit where the total resistance will be 4 ohms.

The problem states that I have to use ALL of the resistors..making it so complicated


Homework Equations


1/Req = 1/R1 + 1/R2 + 1/R3... (in parallel)
Req + R1+R2+R3... (in series)


The Attempt at a Solution


The closest I got was (1/12) + (1/(24+36)) + (1/36) + (1/12) + (1/24). Is there a trick or something..

I could have 4 parallel resistors.. 12 parallel to 12 parallel to 24 parallel to 24.
(1/24) + (1/24) + (1/12) + (1/12) = 1/4 ... but I did not use the 2 x 36 ohms.. help will be appreciated.
 
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Welcome to PF;
I don't think there's a trick exactly - beyond understanding the problem.
i.e. since all the resistors are greater than 4ohms, you will need to combine a lot in parallel to reduce the overall resistance.

Also 12, 24, and 36, are all multiples of 4... your target resistance.

I guess you could design the circuit with a short circuit across unwanted resistors... but that is usually considered the same as not using them.
 
Hm ... I tried a few combinations and I can't get it either. My attempts were hardly exhaustive, but I sure don't see it.
 
3.9560Ω (the closest so far) is 4.0Ω rounded :)

Then there is the 12s and 24s in parallel, in series with the 36's in parallel - but short-curcuit the 36s :)

Since all values divided by 3 as well as 4 I figured looking at triples.
12 = 4x3x1
24 = 4x3x2
36 = 4x3x3

Then there is just trying every possible combination of series and parallel.
I don't think there would be more than two series sections... there won't be that many combinations.
 
Thank you guys, I'll just stick with the 3.9560ohms answer.
 

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