- In 1827, a German physicist Georg Simon Ohm (1787–1854) found out the relationship between the current I, flowing in a metallic wire and the potential difference across its terminals.
- The potential difference, V, across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature remains the same. This is called Ohm’s law. In other words –
- V ∝ I or V/I = R (constant)
- V = IR
- R is a constant for the given metallic wire at a given temperature and is called its resistance.
- It is the property of a conductor to resist the flow of charges through it.
- Its SI unit is ohm, represented by the Greek letter Ω.
- current through a resistor is inversely proportional to its resistance.
- If the resistance is doubled the current gets halved. In many practical cases it is necessary to increase or decrease the current in an electric circuit.
- A component used to regulate current without changing the voltage source is called variable resistance.
- In an electric circuit, a device called rheostat is often used to change the resistance in the circuit.
- FACTORS ON WHICH THE RESISTANCE OF A CONDUCTOR DEPENDS
- (i) on its length – directly proportional to its length (l)
- (ii) on its area of cross-section – inversely proportional to the area of cross-section (A).
- (iii) on the nature of its material.
