Ideal Batteries' Internal Resistance

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The discussion focuses on calculating the internal resistance of a battery modeled as an ideal emf of 12 V with an internal resistance in series. Given the measured terminal voltage of 11.61 V and the values of five resistors, the relationship between the battery voltage, internal resistance, and external resistance is explored. The relevant equations include the voltage across the battery terminals and the total external resistance in series and parallel configurations. The attempt at a solution indicates a need to consider the potential divider effect to accurately determine the internal resistance. The conversation emphasizes the importance of correctly applying circuit theory to solve for the battery's internal resistance.
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Homework Statement


A circuit is constructed with five resistors and one real battery as shown above right. We model. The real battery as an ideal emf V = 12 V in series with an internal resistance r as shown above left. The values for the resistors are: R1 = R3 = 59 Ω, R4 = R5 = 79 Ω and R2 = 140 Ω. The measured voltage across the terminals of the batery is Vbattery = 11.61 V.
What is r, the internal resistance of the battery?

Homework Equations


Vb = Vo((R/r)/(1+R/r))
Vb= voltage across battery terminals
Vo= Internal voltage
r= internal resistance
R= external resistance
Total ext. resistance in parallel: 1/Rt= 1/r1 + 1/r2
total ext. resistance in series: Rt = r1 + r2

The Attempt at a Solution


Taking total resistance dividing by the amperage.
 
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No figure attached.
 
Taking total resistance dividing by the amperage.

That would just give you the ideal voltage which is already known.

Hint: Potential divider
 

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