Definition : According to the Ohm’s law at constant temperature, the current flowing through a conductor is directly proportional to the potential difference across the conductor.
Thus, if I is the current flowing through a conductor and V is the potential difference (or voltage) across the conductor, then according to Ohm’s law.
I ∞ V (when T is constant)
where R is a constant called the resistance of the conductor.
Equation (i) may be written as,
V = I × R ……(ii)
Unit of resistance
The SI unit of resistance (R) is ohm. Ohm is denoted by the Greek letter omega (Ω).
From Ohm’s law,
Now, if, V = 1 volt and I = 1 ampere
Thus, 1 ohm is defined as the resistance of a conductor which allows a current of 1 ampere to flow through it when a potential difference of 1 volt is maintained across it.
Results of Ohm’s law
- Current flowing through a conductor is directly proportional to the potential difference across the conductor.
- When the potential difference in a circuit is kept constant, the current in inversely proportional to the resistance of the conductor. I∝ 1/R
- The ratio of potential difference to the current is constant. The value of the constant is equal to the resistance of the conductor (or resistor). V/I = R