Common Misconceptions

⚠️ Common Misconceptions

Misconception 1: "The gradient of an I-V graph gives resistance"

This is a very common error. The gradient of an I-V graph is I/V, which equals 1/R (not R). To find resistance from an I-V graph, use R = V/I by reading off coordinates at any point, then dividing voltage by current. Steeper gradient = lower resistance (not higher).

Misconception 2: "The filament lamp curve is because current doesn't flow at low voltage"

Even at low voltages, current flows through a filament lamp. The curve through the origin means that some current flows even at tiny voltages. The curve bends because resistance increases as the filament heats up — not because current is blocked at low voltage.

Misconception 3: "A diode doesn't conduct at all in reverse bias"

In practice, a tiny "leakage current" does flow through a diode in reverse bias — it's just so small (microamps) that it's negligible in most circuits. GCSE questions treat the reverse resistance as infinite and reverse current as zero, which is a reasonable simplification.

Misconception 4: "You can put the ammeter in parallel"

An ammeter must always be in series with the component it is measuring current through. Placing it in parallel would short-circuit the component and potentially damage the ammeter (ammeters have very low resistance). The voltmeter goes in parallel.