Physics Topics cover a broad range of concepts that are essential to understanding the natural world.
What is the Source of Electromotive Force or of EMF?
To maintain flow of water in a pipe external force is to be applied. Similarly, to maintain flow of current in a conductor some sort of force is required. The physical quantity supplied by the source of electricity is known as the electromotive force. Force and electromotive force are two different physical quantities. i.e., electromotive force is really not a force, as understood in mechanics.
In the sources of electricity like electric cell, dynamo etc. when even an external energy is converted to electrical energy, an electromotive force is said to have developed.
Definition: The amount of electrical energy produced for transferring a unit positive charge from the lower to the higher potential inside an electric source, is called the electromotive force or emf of the source i.e.,
electromotive force \(=\frac{\text { amount of electrical energy }}{\text { quantity of charge transferred }}\)
Unit: According to the above definition the unit of electro-motive force is J ᐧ C-1. Also joule/coulomb is known to be equal to volt [see Chapter ‘Electric Potential’]. So the unit of electro-motive force is volt (V) which is also the unit of electric potential and potential difference.
The usual definition of electromotive force: When a source of electricity does not send current in an external circuit i.e., when the circuit is open, the potential difference between the two ends of the source is called its electromotive force.
Classification of the Source of Electricity
Electric cell: The source of electricity which does not contain any moving machinery inside it is generally called an electric cell. For example—chemical cell, solar cell, photoelectric cell, nuclear cell.
Dynamo: The source of electricity which has a moving machinery is called a dynamo.