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)???


  • $\begingroup$ This is a repeat of this recent question by the same OP: physics.stackexchange.com/questions/293786/… $\endgroup$
    – freecharly
    Nov 20, 2016 at 19:08
  • $\begingroup$ 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 $\endgroup$ Nov 20, 2016 at 19:28
  • $\begingroup$ 3 more versions of this question of the OP are found here: physics.stackexchange.com/questions/293043/… physics.stackexchange.com/questions/293182/… physics.stackexchange.com/questions/293541/emf-of-an-ideal-cell $\endgroup$
    – freecharly
    Nov 20, 2016 at 19:28
  • $\begingroup$ 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. $\endgroup$
    – freecharly
    Nov 20, 2016 at 19:37
  • $\begingroup$ @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). $\endgroup$ Nov 20, 2016 at 19:41

1 Answer 1


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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