Resistance — Sketch

Sketch and explain the current-voltage graphs for a fixed resistor, a filament lamp, and a diode.

A fixed resistor (at constant temperature) gives a straight line through the origin, showing current is directly proportional to voltage - its resistance stays constant. A filament lamp gives a curve that bends towards the voltage axis (gradient decreases) as current increases, because the filament heats up and its resistance rises. A diode conducts easily in one direction once a small forward voltage is exceeded (current rises steeply), but allows almost no current to flow in the reverse direction (very high resistance).