Difference Between Potential Difference and EMF

A battery is a component in the electrical circuit that transforms energy from a non-electrical form. It converts chemical reactions into electrical energy. The circuit is completed when the electrons travel through wires from the terminals of a battery to the device.

EMF is a measure of an electric current’s electromotive force (a measure of actual output voltage). It occurs when the voltage of the electric current changes.

Potential Difference occurs when two points in space have different concentrations of charge or when two points in space have different velocities and consequently different electric fields but are otherwise identical.

Actual Output Voltage

The actual output voltage is the difference between the highest and lowest voltages on a power source. While you can find both positive and negative output voltages, most power sources only have one voltage in use at any given time. An output is a single value used to represent any voltage on the power source. Even if the voltages change among the various output components, you can still get a single number for a given output. When multiple voltages are used for different components inside a single output, you will still see two numbers (the two highest and two lowest) as you saw when looking at how much actual output voltage is in the battery. This enables one to look at a particular combination of all the voltages in the output. 

Terminals of a Battery

To understand why we chose to name the terminals of a battery “High Voltage” and “Low Voltage”, instead of just calling them positive and negative, you have to understand what electric current does in your car. Regardless of which charging systems are being used, a battery is (generally) charged by an alternator. If a battery has a charge voltage of 14 volts, it will create 14 volts across the terminals. This means that the terminal connected with 14 volts will be an open circuit.

EMF

Electromotive force is a term that describes the current that flows between two points. In other words, it’s the amount of electric charge that’s transferred from one point to another. If there is no “Electric Field”, then there’s no way for electric charge to flow (technically true in the case of no actual output voltage). If there is no flow of charge, you can’t have an “Electric Field”; therefore, EMF isn’t a thing. The electrons are not being magically propelled through space by an “EM Force Field” (this is where the idea of an EM Wave comes from); it is only owing to the positive charge on a battery that the electrons want to start flowing.

Potential Difference

This is just a technical term for the voltage between two points. Typically, a battery (as well as other power sources) will have a “Low Voltage” and a “High Voltage”. The difference between these two voltages is what we call the potential difference. In other words, the potential difference is just another way of describing the difference in voltage between any two surfaces on a power source. If the potential difference between two points is higher, more current (a greater flow of charge) will flow between those two points. This is just another way of describing the High Voltage and Low Voltage outputs. 

Difference between Potential Difference and EMF

Conclusion

In the first part of this article, we’ve discussed the basic concepts behind the electromotive force, actual output voltage, and potential difference. We also talked about some of the characteristics specific to Electromotive Force Fields. So far, it’s been discussed how electrodes, terminals of a battery, and alternators work together to give us the voltage we need to power our vehicles. In the second part of this article, we’ve talked about two specific ways to measure Electromotive Force Field strength and potential difference. In the latter part of the article, we learned many differences between the Potential Difference and EMF.