To measure the emf of a battery, one can connect it in a circuit with a resistor, a voltmeter and an ampere meter. The emf will be the sum of the voltage differences across the resistor and the battery itself: E = U ext + U int. Since U int = I r, where r is the internal resistance of the circuit, the equation can be rearranged as Uext = E - I r.
EMF (ϵ) is the amount of energy (E) provided by the battery to each coulomb of charge (Q) passing through. How do we calculate EMF? The EMF of the cell can be determined by measuring the voltage across the cell using a voltmeter and the current in the circuit using an ammeter for various resistances.
The electromotive force is the work done by a battery on the charge carriers to transport them across the entire circuit, per unit charge. It can be thought of as the specific energy given to the charge carriers. To measure the emf of a battery, one can connect it in a circuit with a resistor, a voltmeter and an ampere meter.
To measure the actual EMF, you measure U when the current supplied from the battery is precisely 0. To do this, traditionally, you don't use a voltmeter but an ammeter ... and a device for measuring potential - that is, a potentiometer.
The combination of chemicals and the makeup of the terminals in a battery determine its emf. The lead acid battery used in cars and other vehicles is one of the most common combinations of chemicals. Figure 10.2.3 shows a single cell (one of six) of this battery.
The EMF represents a large portion of the terminal voltage predicted by electrical models, i.e., it predominantly determines the voltage of the battery. In fact, electrical battery models only differentiate themselves in the way the overpotential is modelled, i.e., the voltage behaviour as a result of excitation .