How to measure EMF of a Cell?

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Practically, if you have a battery connected to only a voltmeter, the internal resistance of a voltmeter is so large that you can neglect the amount of current and so neglect the difference between the terminal voltage and the emf in that case.

If you really wanted to be super correct about things, you could measure the terminal voltage and current with various load resistances, plot the points for the current and the voltage and then extrapolate to the zero current case. I don't think anyone actually does that, though.

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Perspicacious
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Updated on November 21, 2020

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  • Perspicacious
    Perspicacious almost 3 years

    Ok, Emf is the voltage in a cell when no current flows through the circuit.
    Then how do we measure it?

    If one says that connect the cell (of unknown emf) having some finite internal resistance with the voltmeter(assume it is ideal) in parallel and u will get the emf of the cell.

    Now my question is if I do this, this means that the cell is sending some current through the circuit which further means that I have calculated the terminal voltage(voltage across the terminals of the cell which sends the current in circuit).

    And we know that when a cell discharges emf is greater than the Terminal Voltage

    So how to measure the emf of a cell(if I am not wrong till here)???

    Thanks

    • freecharly
      freecharly almost 7 years
      This is a repeat of this recent question by the same OP: physics.stackexchange.com/questions/293786/…
    • Perspicacious
      Perspicacious almost 7 years
      well I am sorry if it is. Can you please tell how both are related to each other @freecharly. If you know then please comment or answer
    • freecharly
      freecharly almost 7 years
    • freecharly
      freecharly almost 7 years
      Maybe it would be best if you explain yourself what the relation of the present question to the four earlier questions is. I think you should update the latest question in this sense.
    • Perspicacious
      Perspicacious almost 7 years
      @freecharly all the questions were asked by me. if I had some intention that all 3 are same then I would not have asked for. Really i don't get how all these posts are related to each other. If you know then please answer in this post.Sorry for such inconvenience and thanks for pinpointing(But i really don't know how they are related to each other).
    • freecharly
      freecharly almost 7 years
      In case you have not noticed yourself: all your 5 question are about the significance of the EMF of a cell.
    • freecharly
      freecharly almost 7 years
      Here is the sixth question on the same subject: physics.stackexchange.com/questions/293767/…
  • Perspicacious
    Perspicacious almost 7 years
    thanks david and another question why emf is independent of internal and external resistance? You can answer the question by following the link. physics.stackexchange.com/questions/293786/…