Combined Circuit Total Resistance

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Discussion Overview

The discussion revolves around calculating the total resistance of a combined circuit consisting of lightbulbs arranged in series and parallel configurations. Participants are exploring the relationships between voltage, current, and resistance in the context of a homework problem.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • The original poster has calculated the resistances of individual bulbs and is seeking the total resistance of the entire circuit.
  • One participant requests a visual representation of the circuit to better understand the configuration.
  • Another participant questions whether the three bulbs are the only resistances in the circuit and suggests that the total resistance can be found by combining the series and parallel resistances as described.
  • A different participant points out a potential inconsistency in the voltage measurements, noting that the sum of the voltages across the series bulbs does not equal the voltage across the parallel bulb, raising concerns about the accuracy of the measurements.
  • This participant also emphasizes the importance of mathematical relationships in series and parallel circuits, suggesting that the current measurements imply equal resistances in the branches.

Areas of Agreement / Disagreement

Participants express differing views on the validity of the measurements and calculations presented. There is no consensus on the correctness of the total resistance calculation or the implications of the voltage discrepancies.

Contextual Notes

Participants have not resolved the implications of the voltage measurements or the assumptions regarding the battery's resistance. The discussion includes various interpretations of the circuit's behavior based on the provided data.

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Homework Statement


OK so I have calculated the total resistance for the series and parallel part of the circuit. Now I just need help with the total


Homework Equations


Experimental Results:
Bulb 1: Volts = 3 Current = 0.46 Resistance1 = 3 ÷ 0.46 = 6.5
Bulb 2: Volts = 3 Current = 0.46 Resistance2 = 3 ÷ 0.46 = 6.5
Bulb 3: Volts = 5.5 Current = 0.46 Resistance3 = 5.5 ÷ 0.46 = 11.9
Total Resistance(series) = Resistance1 + Resistance2 = 6.5 + 6.5 = 13
Total Resistance(parallel) = 1 ÷ (1 ÷ R1) + (1 ÷ R2) + (1 ÷ R3) = 6.7

What is the equation to find out the Total Resistance of the whole circuit.
 
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Can you show the circuit?
 
[PLAIN]http://img31.imageshack.us/img31/7056/circut.png

there's the 3 lighbulbs, on the right is the switch and the top part is the power pack.

Thanks for the quick response
 
Last edited by a moderator:
Are the three bulbs the only resistances in the circuit?

Then all you would have to do is find the total resistance of the lightbulbs which I believe you did. The two in series and then that in parallel with the other bulb should be the total resistance assuming the battery's resistance to be negligent.
 
If the circuit is set up like that, then the sum of the voltages across Bulb 1 & 2 (series branch) should be the same as Bulb 3 (parallel branch).

3 + 3 != 5.5 (close enough is good enough maybe?)

If the current you measure through each branch is 0.46A then the resistance of each branch is equal and the current is being split equally between branches.

6.5 + 6.5 != 11.9 (close enough is good enough again?)

You can remember that two equal resistances in series will double the value, two equal resistances in parallel will halve the value. Math is always better though.
 

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