Resistance Circuit Homework: Solving for Total Resistance

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Homework Help Overview

The discussion revolves around a resistance circuit problem, specifically focusing on calculating the total resistance in a circuit with resistors in both parallel and series configurations. The original poster attempts to solve for total resistance using the formula V=IR and presents their calculations.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss methods for determining the equivalent resistance of resistors in parallel and series. Some suggest starting with the resistances of R2 and R3, while others question the original poster's calculations and approach. There are inquiries about how to address the first question regarding the potential difference across the circuit.

Discussion Status

There is ongoing exploration of different methods to calculate total resistance, with some participants providing guidance on the relationships between the resistors. Multiple interpretations of the circuit configuration are being discussed, and hints are offered without reaching a consensus on the final approach.

Contextual Notes

Participants note the importance of understanding the current relationships in the circuit and the implications of Ohm's Law in the context of parallel and series resistors. There is mention of a specific current value through R2 that influences the calculations.

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Homework Statement



http://i1103.photobucket.com/albums/g480/Alfredo24PR/physicssucks.jpg"

Homework Equations



V=IR

The Attempt at a Solution



I tried adding the resistance:

1/8 + 1/ (6+5+10) = 1/8 + 1/21 = 0.1726

1/0.1726 = 5.793 ohm
 
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You could start out by determining the resistance of the whole circuit. R2 and R3 are in parallel. You can find a resistance for them. Together, they are in parallel with R1. You can determine this resistance. This is in series with R4. The result is the total resistance of the circuit.

Keep in mind the sum of the currents passing through R1, R2, R3 must equal the current passing through R4. Be careful how you compute effective resistance for resistors in parallel and series.
 
LawrenceC said:
You could start out by determining the resistance of the whole circuit. R2 and R3 are in parallel. You can find a resistance for them. Together, they are in parallel with R1. You can determine this resistance. This is in series with R4. The result is the total resistance of the circuit.

Keep in mind the sum of the currents passing through R1, R2, R3 must equal the current passing through R4. Be careful how you compute effective resistance for resistors in parallel and series.

Ok, I figured out the middle ones and you explained the last one.

How do I start with the first question: "What potential difference must be applied to the external terminals?"
 
One way to go at it would be to guess a voltage over the whole system. This allows you to compute the voltage drop through R4. Subtract that from the applied guessed voltage and you get the voltage drop across the inner part of the circuit. Knowing that you can compute the current through the 'inside' resistors. Keep reguessing until you get 4 amps through R2.
 
alfredo24pr said:
I tried adding the resistance:

1/8 + 1/ (6+5+10) = 1/8 + 1/21 = 0.1726

1/0.1726 = 5.793 ohm

Your formula doesn't look right. Note that while R1, R2, and R3 are in parallel, R4 is in series with that parallel group.

Here's a big hint :smile:. If you're given the current through resistor R2 then you automatically know the voltage across it (Ohm's Law). What do you know about the voltage across parallel components?
 

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