Electromotive Force is the force on electrical source its an electrical energy which passes through a complete circuit the short form electromotive force is emf. The difference between electromotive force and potential difference or voltage is electromotive is the cause and potential different is the effect. Electromotive force is the source which cause current and potential difference is the voltage of two points in any circuit. If there is no electromotive force there will be no potential difference. Electromotive force is independent but potential difference or voltage is dependent to the source if the source is absent there will no voltage in two points. 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 electromotive 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).
Difference between potential difference and electromotive force
Electromotive force and potential difference are not same. They have following differences below
- What is electromotive force? The potential difference between the two terminals of a cell is called electromotive force in an open circuit.
- Electromotive force transmits current both inside and outside the cell.
- Electromotive force emf is the cause.
- Electromotive force is always greater than potential difference.
- Electromotive force creates potential difference entire the circuit.
- Electromotive force does not depend on the resistance of the circuit.
- Electromotive force remains constant.
- The part of the circuit where electrical energy is created from any other energy then that part contains the source of Electromotive force.
- What is potential difference in a circuit? Bringing a unit positive charge from one point to another point in a circuit is called potential difference between two points.
- Potential difference current transfers between any two points in the circuit.
- Potential difference is the result.
- Potential difference is always less than electromotive force.
- Potential difference takes place between any two points in the circuit.
- Potential difference of two points depends on the resistance of those points.
- It does not remain constant.
- Potential difference exists in the part of the circuit where electrical potential energy is transformed into another form of energy.