Ohm’s law states that the__ electric current, I flowing through a conductor is directly proportional to the potential difference across the ends of the conductor __, if temperature and other physical conditions remain constant.Mathematically, Ohm’s Law is written:

V = IRwhere

V = potential difference [V]

I = current [A]

R = resistance [Ω]

Ohm’s Law tells us that if a conductor is at a constant temperature, the voltage across the

ends of the conductor is proportional to the current. This means that if we plot voltage on the

y-axis of a graph and current on the x-axis of the graph, we will get a straight-line. The

gradient of the straight-line graph is then the resistance of the conductor.

The resistance,

R is a term that describes the opposition experienced by the electrons as they flow in a conductor. It is also defined as the ratio of the potential difference across the conductor to the current,

I flowing through the conductor.

Non-ohmic conductorsNon-ohmic conductors are conductors which do not obey Ohm’s Law.

E.g., a light bulb whose resistance increases over time due to temperature increase (heating effect of current)

In general non-ohmic conductors have plots of voltage against current that are curved,

indicating that the resistance is not constant over all values of voltage and current.

Worked example :

Question :

What is the value of the resistor in the figure, if the dry cells supply 2.0 V and the ammeter reading is 0.5 A?Solution :

V = IR2.0 = 0.5 (R)R = 4 Ω

Simulation