Ohm’s Law, Resistance & Resistivity — A/L Physics

Ohm’s Law At constant temperature, the current through a conductor is directly proportional to the potential difference across it. This means V ∝ I , or V = IR , where R is constant for a given conductor at a fixed temperature. Ohm’s law is not a universal law; it applies only to ohmic materials (e.g., metals) where resistance remains constant. For example, a copper wire at room temperature obeys Ohm’s law, but a filament bulb does not because its resistance increases with temperature.

Resistance (R) The opposition a material offers to the flow of electric current, defined as R = V/I . Resistance depends on the material’s nature, dimensions, and temperature. A longer wire has higher resistance, while a thicker wire has lower resistance. In circuits, resistors are used to control current; for instance, a 100 Ω resistor limits current more than a 10 Ω resistor for the same voltage.