# Electric potential difference and the electromotive force

### Electric potential difference of a conductor

The electric potential of a conductor is the state of an electric conductor that shows the transfer of electricity to and from it when it is connected to another conductor , It is from the physical properties of the electric current .

If two charged conductors touch or are connected with wire and one of them conductor ( A ) has electric potential higher than the other conductor ( B ) , Electric energy ( in the form of electric current ) will flow from ( A ) to ( B ) until their electric potential become equal .

The transference of charges does not depend on their amount , But it depends on the difference in their potential , When two conductors have the same electric potential and they are connected by a wire , No electric current will pass through them , because there is no potential difference between them ( the potential difference equals zero ) .

The potential difference across two terminals of a conductor is the value of the work done to transfer a quantity of charge ( one coulomb ) between the two poles of this conductors , The potential difference measuring unit is the volt , The measuring unit of the work is the Joule , And the measuring unit of electricity is the Coulomb .

Voltmeter

##### 1 Volt = 1 Joule / 1 Coulomb

The volt is the potential difference across two terminals of the conductor on doing the work of one joule to transfer the quantity of charge of one coulomb , The joule is the amount of work done by the force of one Newton to move the object through a distance of one meter .

### The electromotive force

The electric source ( the electric cell or the battery ) acts as a pump to maintain a continuous flow of the electric current in the electric circuit , The power of this electric source is known as the Electromotive force ( e.m.f. ) .

Electromotive force ( e.m.f. ) is the potential difference between the two poles of the battery when the electric circuit is open ( no current passes through the circuit ) , The measuring unit of the e.m.f. is the Volt .

The apparatus used in measuring the potential difference and the ( e.m.f. ) is called the voltmeter and it is given by the symbol V in the circuit ,  the voltmeter is connected in parallel between the two terminals of the conductor to measure the potential difference in a closed circuit .

The voltmeter is connected in the electric circuit in parallel between the poles of the dry cell or the battery to measure the electromotive force ( e.m.f. ) of the battery in an open circuit .

##### The electric potential at home and in the electric equipments

The electric voltage at home is 220 volt . the big electric appliances such as the washing machines and the dishwashers are relatively high voltages of 110 – 240 volts , but the electronic devices such as the mobile cell phones use relatively tiny voltages .

If you connect the device of low voltage directly at your home that has 220 volts source , that device wil break down , So , You should use a device known as the electric transformer ( step-down transformer ) to reduce the electric potential of the source .

Electrical current , Potential difference , Electric resistance and Ohm’s law

Resistances connection ( series & parallel ) , Electric energy and Electric power

Ohm’s Law for the closed circuit , Relation between emf ( VB ) of an electric cell & voltage across its poles