What is electromotive force? What's its relationship to Voltage?

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Discussion Overview

The discussion centers around the concept of electromotive force (EMF) and its relationship to voltage, exploring definitions, conditions under which they are equal or differ, and implications in circuit analysis. The scope includes theoretical explanations and practical applications in electrical circuits.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant defines electromotive force as the potential difference between two points before they are connected.
  • Another participant describes two cases regarding the relationship between EMF and voltage:
    • Case 1: EMF equals voltage in ideal circuits with no resistance or energy loss.
    • Case 2: EMF is greater than voltage in practical circuits due to resistances and energy losses.
  • A participant notes that voltage at the output terminals of a power source in an open circuit is equivalent to the EMF, aligning with Case 1.
  • It is mentioned that when a power source is connected to a load with finite resistance, the voltage drops based on internal resistance and current drawn, corresponding to Case 2.

Areas of Agreement / Disagreement

Participants present differing views on the relationship between EMF and voltage, with some agreeing on the definitions and conditions while others provide additional context or challenge earlier claims. The discussion remains unresolved regarding the nuances of these concepts.

Contextual Notes

There are limitations in the discussion regarding assumptions about ideal versus practical circuits, the definitions of EMF and voltage, and the implications of internal resistance in power sources.

StoicIndieHacker369
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New poster has been reminded to post their whole question at PF and not just link to external websites.
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This was a question that I posted on the Physics stack exchange, but I'm posting it here to have a higher probability of receiving an adequate answer.
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It is fine to post the question on both sites, but not this way. The question should be self contained on each site so that people can understand what you are asking on each site directly.
 
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Likes   Reactions: Vanadium 50
I will answer your question but only the one here on PF.

Electromotive force is basically the potential difference between two points before they are connected .

Now there are two cases after connection is made between the points of 2 different potentials

Case 1: EMF = Voltage
This happens when there is no resistance and no loss of energy (only possible in ideal circuits) and there is no internal resistance in the voltage source

Case 2: EMF > Voltage
This happens in practical circuits we see in daily life . Here the components have resistances , charges leak , voltage source has internal resistance and energy is lost as heat/light .

Voltage can never be greater than EMF as EMF is a perfect tendency or a perfect potential difference(EMF is in a open circuit ) but voltage is the the result of applying EMF in a closed circuit
 
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In circuit analysis, voltage at a the output terminals of a power source that is open circuit is taken as the same thing as the EMF inside the power source. This is case 1 above.

When the power source is connected to something with finite resistance the voltage drops according to both (1) the amount of internal resistance in the power source prior to the output terminals, and (2) the amount of current drawn by the load. This is case 2 above. Zero internal resistance, or infinite external load, would mean that the terminal voltage is the same as the EMF, just as in case 1 above.
 
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