Ohm's Law

Ohm's Law states that the current, I, passing through a conductor is directly proportional to the potential difference, V, between its ends, provided that the physical conditions and temperature remains constant. Thus, I \propto V.

• Conductors which give a constant ratio of V to I are known as ohmic conductors

Ohmic conductor

• I \propto V; it is a straight line graph passing through the origin for IV graph with k = constant
• Constant resistance

Non-Ohmic conductor

• R is different for different values of V

I-V Characteristic Graphs

Filament Lamp

• Graph is a curve
• Current I is not proportional to V
• when V is doubled, I is less than doubled
• R increases as current increases

Semiconductor Diode

• Graph is a curve
• In forward direction, current increases very rapidly when voltage > 0.6V
• Diode has very low resistance when p.d > 0.6V
• Reverse diode has very high resistance