What a learner can do afterwards
- Builds a test circuit with an ammeter in series and a voltmeter across the component
- Plots current against potential difference for both directions and describes the shape
- Explains the lamp's curve by its filament heating up, and the diode's shape by current in one direction only
1 · Read
To test a component you build a circuit with the ammeter in series and the voltmeter across the component. Change the supply step by step and record each current with its voltage. Those pairs become the dots of your current against voltage graph.
A fixed resistor gives a straight line through zero, because current rises in step with voltage. The steepness of the line is set by the resistance. A steep line means low resistance, since more current flows for each volt.
A filament lamp starts like a resistor, then its graph bends flat at higher voltages. The filament heats up, its resistance climbs, and current rises more slowly. A diode is stricter: it passes current one way and blocks it the other, so its graph stays near zero on the reverse side and climbs fast on the forward side.
Reverse the supply and the resistor and lamp graphs mirror through zero. The diode keeps its flat side on reverse, which is how you spot it. A lopsided graph means a diode, not a resistor or a lamp.
Straight means steady resistance, a bend means heating, and lopsided means a diode.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.