GCSE-ready- Home
- Lessons
- GCSE & IGCSE Physics
- Resistance and I-V graphs
Resistance and I-V graphs
🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.
Resistance controls how much current flows. Different components give different current to voltage graphs.
Ohm's law
V = I × R: potential difference (V) = current (A) × resistance (Ω).
A bigger resistance means a smaller current for the same p.d.
A bigger resistance means a smaller current for the same p.d.
I-V graphs
Why resistance heats things
As electrons move, they collide with ions in the metal lattice. This transfers energy and heats the wire.
This is useful in heaters and kettles, but wasteful in cables. Low-resistance wires reduce the heating.
This is useful in heaters and kettles, but wasteful in cables. Low-resistance wires reduce the heating.
A 12 V supply drives a current of 0.4 A through a resistor. Find its resistance.
- R = V ÷ I
- R = 12 ÷ 0.4
Answer: 30 Ω
V = I × R. A fixed resistor gives a straight I-V line; a filament lamp curves because resistance rises with temperature; a diode conducts one way.
The interactive lesson includes the diagrams for this topic.
Check you have got it
Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.