(E&M) Don't understand why terminals of battery are switched

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SUMMARY

The discussion centers on the confusion regarding the switching of battery terminals in example 11.9 of the Princeton Review's "Cracking the AP Physics C Exam 2011 Edition." The author initially questions the rationale behind swapping the terminals of a 10V battery while applying Kirchhoff's Rules to determine the current through resistor R2. Clarification is provided that the potential drop is correctly described when moving from the positive to the negative terminal, despite the initial confusion over the terminal orientation. Ultimately, the consensus is that the terminal switch was likely a typographical error in the circuit diagram.

PREREQUISITES
  • Understanding of Kirchhoff's Rules
  • Familiarity with circuit diagrams
  • Basic knowledge of voltage and potential difference
  • Experience with analyzing electrical circuits
NEXT STEPS
  • Review Kirchhoff's Voltage Law and its applications in circuit analysis
  • Study common circuit diagram notations and potential sources of error
  • Practice problems involving battery configurations and terminal orientation
  • Explore the implications of potential drop in series and parallel circuits
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Students studying AP Physics, educators teaching circuit analysis, and anyone seeking to clarify concepts related to electrical circuits and potential differences.

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In the Princeton Review Cracking the AP Physics C Exam 2011 Edition book on example 11.9's solution, one of the batteries' terminals are swapped (the battery with 10V). I am not sure why the author's do this considering the current is drawn the same. Later on in the solution, they recognize that the terminals are switched when they state that the potential drops as a result of going from positive to negative (even though originally it was negative to positive).

PROBLEM:
Use Kirchhoff's Rules to determine the current through R2 in the following circuit:
l2eZ37Vl.jpg


WHERE I'M LOST:
I circled the parts of the illustration where the battery terminals are switched.
0a5xpaBl.jpg


During the explanation of the solution, it states that "From e to f, we travel through E2 from the positive to the negative terminal, so the potential drops by E2." so their intentions were to switch the terminals but I'm not sure why we are allowed to do that.

Here is a full page scan of most of the solution(the little bit that is not included here is not necessarily essential in this case)
Dv8JrZjl.jpg
 
Last edited:
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You're not allowed to do that. The original circuit diagram probably just has a 'typo.'
 
Ok, I see now. Thanks for the clarification.
 

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