Understanding Electromotive Force and Internal Resistance in Batteries

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Discussion Overview

The discussion revolves around understanding electromotive force (emf) and internal resistance in batteries, focusing on how these concepts affect voltage readings in different circuit conditions. Participants explore theoretical aspects and practical measurement techniques related to batteries.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that the emf can be measured by opening the circuit, while questioning how voltage readings differ when the circuit is complete due to internal resistance.
  • Another participant refines the first claim by stating that voltage drop occurs due to current flowing through the internal resistance of the battery.
  • There is a query about the necessity of measuring voltage across two points rather than directly at the battery terminals, with a suggestion that internal resistance is related to the battery's construction.
  • A third participant emphasizes the importance of using a multimeter to measure values before understanding circuit completion, noting that electrons flow from positive to negative when the circuit is closed.
  • A fourth participant states that to accurately measure emf, one must avoid drawing significant current from the source and recommends using a voltmeter with high input impedance for better accuracy.

Areas of Agreement / Disagreement

Participants express differing views on the measurement of voltage in relation to internal resistance and emf, indicating that multiple competing perspectives exist without a clear consensus.

Contextual Notes

Some limitations include assumptions about the definitions of internal resistance and emf, as well as the conditions under which measurements are taken, which remain unresolved.

yuganes warman
uploadfromtaptalk1426328363255.png

sorry for the drawing.Hope you guys can bear with it.
The electromotive force can be calculated by opening the switch and the voltmeter will show the exact voltage of the battery. When the switch is closed,there will be a voltage drop due to the internal resistance of the battery. The question is, there will be a potential different across the two points between the battery when the circuit is incomplete which will show the exact voltage of the battery,but does the same goes to reading of the voltage given that the circuit is complete ? Why ? (please refer to the drawing)
another question, if there is an internal resistance within the battery why do they requirre the two points ? and why not just connect the voltmeter to the positve and negative terminal of the battery ? Thanks !
 
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yuganes warman said:
there will be a voltage drop due to the internal resistance of the battery
More correct: A voltage drop due to the current through the battery and the internal resistance of the battery.
yuganes warman said:
another question, if there is an internal resistance within the battery why do they requirre the two points ? and why not just connect the voltmeter to the positve and negative terminal of the battery ?
The internal resistance is not a resistor, it is due to the construction of the battery. The internal resistance is defined as the drop in battery voltage divide by the current drawn from the battery.
yuganes warman said:
The question is, there will be a potential different across the two points between the battery when the circuit is incomplete which will show the exact voltage of the battery,but does the same goes to reading of the voltage given that the circuit is complete ? Why ?
Sorry, I have no idea what you are asking.
 
Best to have a multimeter to measure the respective values before trying to understand the completion of a circuit. Electrons flow from positive to negative between two points upon the closing of a circuit. <link deleted>
 
Last edited by a moderator:
To measure the emf of a voltage source you must not draw any current (or very little current) from the voltage source during the measurement. When using a voltmeter use one with a high input impedance ( resistance) usually rated by the number of ohms per volt measured. Best above 1 megaohm per volt. For the best accuracy use the potentiometer circuit below the accuracy of which is only limited by the accuracy of the standard cell and the ratio of the resistance arrived at in its adjustment.

upload_2015-3-14_15-37-53.png
 

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