We use radio, television, refrigerators tube light etc in our home appliance. To operate these appliances we need electric energy. There are many kinds of sources of electrical energy like generator, electric cell or battery.
Let us consider a torch light. There are two or there dry cell in series combination is called battery. Copper plate and a small bulb connection with the battery. The source of energy in the torch light is battery because it supplies current here. Electric energy transfers from the battery to the bulb and the filament of the bulb heated and radiates light.
Due to chemical reaction in the battery charges travel one terminal to another terminal. So, one terminal becomes positively charged and one is negatively charged.
Having the positive and negative charge in the two terminals of the cells a potential difference creates between two terminals.
The maximum potential difference that exists between the terminals of the cell when it is disconnected from the external circuit is called electromotive force emf of the cell.
If we connect an external resistance R which is small r, it remains inside the cell. The current will continue to the R until disconnection of the circuit or the damage of cell. It can be said that cell is the driving force which maintains current flow in the circuit.
So, another definition of the electromotive force is “The driving force which keeps or maintains the flow or current in the circuit is called electromotive force. The short name of electro motive force is emf. It is denoted by E.
Unit of emf: The unit of emf electromotive force is volt (V) or Joule/ Coulomb (J/C).