Basic EMF Problem: Find r Given E, R, and V

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Homework Help Overview

The problem involves a battery with an electromotive force (emf) E and an internal resistance r, connected to an external resistor R. The potential differences across the circuit are given for two different values of R, prompting a need to find the internal resistance r.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationships between the emf, internal resistance, and potential differences. There are attempts to express one variable in terms of another, but confusion arises due to the presence of two unknowns. Questions are raised about the specific circuit elements referenced by the potential differences and the clarity of the problem statement.

Discussion Status

The discussion reflects a mix of confusion and exploration of the problem's setup. Some participants seek clarification on the question being asked, while others express frustration over the lack of a clear path to a solution. There is no explicit consensus on how to proceed, but suggestions to derive relationships between the variables are noted.

Contextual Notes

The original poster indicates that the problem is part of a larger set of homework assignments, which may add to the pressure and complexity of understanding the current problem.

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Homework Statement



A battery has an emf E and an internal resistance r. IT is connected to an external resistor R. When R=4 ohms, the potential difference is 9.5 V. When R = 6 ohms, the potential difference is 10.0 V

Homework Equations





The Attempt at a Solution


Rtotal = R + r
I = V/Rtotal
E = V/Rr + V_ba
when I equate both to try to solve for r, I still end up getting an unknown of 2 variables. Any help would greatly be appreciated. Thank you.
 
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When you say the potential difference is 9.5 V and then 10 V you are referring to the potential difference across what circuit element? Also, what is the question? The internal resistance of the battery?
 
That's just how the problem is given. I am totally lost, and what's worse is, the rest of the homework problems I have to do builds on top of this. I been at this for the past 2 hours and I keep running into 2 unknowns. Can anyone please provide a solution for this? Thanks
 
The problem is not asking a question, so there's nothing to solve for. If you want to describe the system mathematically then just solve for one variable in terms of the other variable. You may not know was both variables are, but you can derive the relationship between them.
 

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