This comparison covers Ohmic vs Non-Ohmic: V-I Graphs within Resistance & Ohm's Law for GCSE Physics. Revise Resistance & Ohm's Law in Electricity for GCSE Physics with 14 exam-style questions and 30 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 10 of 16 in this topic. Use this comparison to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 10 of 16
Practice
14 questions
Recall
30 flashcards
⚖️ Ohmic vs Non-Ohmic: V-I Graphs
| Component | V-I Graph Shape | Resistance Behaviour |
|---|---|---|
| Fixed resistor | Straight line through origin | Constant |
| Filament lamp | S-shaped curve (steeper at high V) | Increases with temperature |
| Diode | Flat near zero then steep rise | Very high (reverse), very low (forward) |
| Thermistor | Depends on temperature conditions | Decreases as temperature rises |
Quick Check: Why does a filament lamp have a curved V-I graph rather than a straight line?
As current increases, the filament heats up. This causes the metal ions to vibrate more vigorously, increasing resistance. Because resistance is not constant, the component does not obey Ohm's Law — the V-I graph curves rather than being a straight line through the origin.