Types of electric resistance ( The resistor ) and Ohm’s law

The electric resistance ( The resistor )

The electric current faces an obstruction ( resistance ) when it passes through a conductor which affects its intensity , The electric resistance is the opposition that the electric current faces during its passing through a conductor , The apparatus used in measuring the electric resistance is called the Ohmmeter .

The measuring unit of the electric resistance is the Ohm , The ohm is the resistance between two points of the conductor when the constant potential difference of 1 volt applied to these points , It produces the current of 1 ampere in the conductor , Types of electric resistance are the constant ( fixed ) resistance , and the variable resistance ( Rheostat ) .

1 Ohm = 1 volt / 1 Ampere

The variable resistance ( Rheostat )

The variable resistance ( Rheostat ) is the resistance that you can change its value in order to adjust the value of the current intensity and the potential in the different parts of the circuit , It is used to control the electric current intensity flowing through the circuit and the potential difference in the different parts of the circuit .

It consists of a metallic wire of high resistance coiled around a cylinder made of an insulating substance as porcelain , and a thin copper sheet that has a sliding contact ( slider ) that can be moved along the wire length .

The idea of operation of the rheostat

By sliding the flexible sheet on the wire , we can control the length of the wire that enters the electric circuit , If we increase the length of the wire , the resistance increases and the current intensity decreases , If we decrease the length of the wire , the resistance decreases and the current intensity increases .

Electric current

Electric current

The relation between the current intensity and the potential difference ( Ohm’s law ) 

The German physicist George Simon Ohm who discovered the quantative properties of the electric current , also discovered a law in the electricity that shows the relation between the electric current and the potential difference which is known as after him by Ohm’s law .

Ohm’s law states that the electric current intensity passing through the conductor is directly proportional to the potential difference across it at the constant temperature , So , the mathematical form of Ohm’s law is .

R = V / I

The potential difference ( V ) is measured in volts , The current intensity ( I ) is measured in amperes , The resistance ( R ) is measured in ohms , The potential difference ( V ) in the circuit is directly proportional to the current intensity ( I ) .

1 Ohm = 1 Volt / 1 Ampere 

The resistance of a conductor is known as the ratio between the potential difference across the two ends of the conductor ( resistor ) and the current intensity passing through it , The ohm is the resistance of the conductor which allows passing the electric current intensity of one ampere when the potential difference between its terminals is one volt .

The ampere is the current intensity passing through a conductor whose resistance is one ohm and the potential difference between is terminals is one volt , The volt is the potential difference across the two terminals of a conductor whose resistance is one ohm and the current intensity passing through it is one ampere .

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

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