# EMF or Electromotive Force

Before introducing the topic I recommend you to read our earlier post on electric potential difference.

Electromotive force or emf defined as the voltage generated by a source when circuit is open. It is the potential difference between two terminal of electric source when circuit is open.

Suppose a resistor is connected across the terminal of a battery. Due to the potential difference between two terminals, current start flowing in the circuit from higher potential to lower. Similarly, electrons will start flow from negative to positive i.e. from lower potential to higher potential.
But the problem took place when electrode reached at positive terminal. It is attracted by the positive terminal and electrons will stop there. To avoid this, inside a battery or electric source work has to be done to bring the electron from higher potential to lower the electric potential i.e. from positive to negative terminal.
Therefore the influence that makes electrons to flow from positive to negative terminal (inside a source) is called as EMF.

Therefore we arrive at a very important conclusion that emf is important to maintain the potential difference.

From the above discussions EMF may defined as the energy supplied to electric charge.

Unit of EMF
Unit of emf is Volt.

Difference between EMF and Electric Potential Difference.
As we discussed that both EMF and electric potential difference are measured in volt but the basic difference between EMF and potential difference is
– An EMF can introduce energy to a system or circuits
– A potential difference dissipates energy in a systems or circuits
An EMF introduce energy into system that can be utilised by the of potential difference.

Are you confused, let’s make this discussion more simple
Keep in mind that both potential difference and EMF are measured in volt
Voltage =  Joule / Coulombs

Suppose a charged particle (electron) is at lower potential and has some store electric potential energy. When circuit is closed electron start moving from lower potential to higher potential i.e negative to positive. During this process electron has to utilise its all store potential energy in external circuit in the form of heat, light etc. When electrons is at higher potential its store potential energy is negligible. Now to bring the electron from higher potential to lower potential i.e. positive to negative, we have to do some work against electric field and this work done is stored in the electron in the form of electric potential energy which can be further dissipate in external circuit in the form of heat, light etc.

Electric potential energy store or give per coulomb of charge is called emf.
Electric potential dissipate or utilize per coulomb of charge is EPD.

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It is clear from the above discussion that
EMF of 10 volt means 10 joule of energy is stored in one coulomb of charge.
Potential difference of 10 volt means 10 joule of energy is dissipated by one coulomb of charge.
EMF refer to creating energy and Potential difference refer to dissipate energy.

What the charged particles do?
Charged particles are used to transfer energy from one part to another in an electric circuits. Charged particle takes energy from source and give it took to load or external circuit. When charged particle moves through source of EMF it gain energy and when pass through road or resistor it losses energy.