9.3.5—Ohm’s law
- Syllabus
- 9702–2028–2029
- Objective
- 9.3.5
- Level
- AS
Ohm’s law is a condition-dependent model, not a universal rule for every component
A component obeys Ohm’s law only when its V–I relation is proportional under constant conditions, giving constant resistance.
Test proportionality experimentally and identify variables such as temperature. Use a non-linear model or a local resistance when the graph curves.
A fixed resistor can be approximately ohmic over its rated range, while a filament lamp fails the test as it warms.
“Resistance” existing for a device does not prove that V/I stays constant across all voltages.
ConceptA-Level CAIE Physics AS