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 16 exam-style questions and 30 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. 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.
⚖️ 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.
Practice questions for Resistance & Ohm's Law
Which of the following best describes electrical resistance?
Explain what is meant by an ohmic conductor.