If I had a 3V battery, and when no load connected it reads 3.2V, and with a load 2.8V (just a hypothetical example), what is the name for these two terms, with a load or no load?

I know the voltage drop occurs due to its internal resistance when a load is connected, however I still am not sure of the terms. Here's a few which may be of help:

  • emf ($\mathcal{E}$)

  • Potential difference

  • Terminal voltage

Any help would be appreciated in what these terms are called, this is one of those questions where it almost seems too simple to find this answer online.

  • $\begingroup$ Well, voltage is another name for electric "potential difference." $\endgroup$
    – HDE 226868
    Aug 11 '14 at 20:13
  • $\begingroup$ Thanks, I know that however I thought it could be a possible answer for the question, so decided to list it anyway. $\endgroup$
    – baharini
    Aug 11 '14 at 20:14
  • $\begingroup$ I figured you knew, but I was trying to eliminate it (although I've been looking at it more and I'm not sure). $\endgroup$
    – HDE 226868
    Aug 11 '14 at 20:16

The voltage across the battery when there is zero current (no load connected) is called the open circuit voltage.

The emf of the battery is equal in magnitude to the open circuit voltage.

I'm not certain that there is a standard term for the battery terminal voltage when a load is connected since, in general, this voltage varies with the load. One might call this the loaded voltage.

For example, modelling the battery as an ideal voltage source with voltage $V_{OC}$ in series with a resistor (to model the internal resistance) $R_{S}$, the voltage across the battery terminals is given by

$$V_{BAT} = V_{OC}\frac{R_L}{R_S + R_L}$$


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