Electromotive force (EMF) is equal to the terminal potential difference when no
current flows. EMF and terminal potential difference (V) are both measured in volts,
however they are not the same thing. EMF (ϵ) is the amount of energy (E) provided
by the battery to each coulomb of charge (Q) passing through. changed to electrical
energy when unit charge passes through the cell
electrical energy produced (in the battery) per unit charge (1)
[or potential/voltage across terminals when there is no current]
How do we calculate EMF?
The EMF can be written in terms of the internal resistance of the battery (r)
where: ϵ = I(r+R)
Which from Ohm’s law, we can then rearrange this in terms of the terminal
resistance: ϵ = V+Ir