How to define Voltages, Electromotive Force (emf), and Potential Difference (PD)?

Last updated on April 14th, 2021 at 02:48 pm

Voltages, Electromotive Force (emf), and Potential Difference (PD) – These 3 terms are often used while we discuss electrical circuits. Hence exactly knowledge about these certainly helps us to understand one circuit. Here we will provide a brief definition or meaning of these three terms.

What is Voltage?

The electrical quantity Voltage is a measure of the amount of energy a component transfers per unit of charge passing through it. It can be calculated from the equation:
Voltage (V) = Energy Transferred (E) / Charge passing (Q)
=> V = E/Q

Using SI units, Volt = Joule / Coulomb

What is Electromotive Force (emf)?

Electromotive force or emf is the correct term for a supply voltage – It’s a component which puts electrical energy into a circuit.

emf(e) = energy supplied (E) / charge passing (Q)
e = E/Q

If a cell supplies 1 Joule of energy per Coulomb of charge that passes through it, then the cell is said to have an emf of 1 Volt (1 V).

What is Potential Difference (pd)?

For a component that is using electrical energy in a circuit and transferring this energy, the correct term for the voltage is Potential Difference (pd).

Potential Difference (pd) = energy used or transferred(E) / charge passing (Q)
pd = E/Q

If a component uses 1 Joule (1 J) of energy per Coulmb of charge (1 C) that passes through it, it has a PD of 1 Volt (1 V).

Conclusion – An example of bicycle light

For any useful electrical circuit, there must be at least one component that can supply electrical energy.

The circuit will also have components that would consume and utilize this energy for some useful purpose.

For example, a bicycle light will have a cell that transfers electrical energy from a chemical reaction. The same light will have a lamp that uses this electrical energy to produce light radiation.