This exam tips covers Exam Tips for Resistance and Ohm's Law 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 15 of 16 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
💡 Exam Tips for Resistance and Ohm's Law
🎯 Common Question Types:
- Ohm's Law calculation: V = IR or R = V/I (2 marks)
- Describe V-I graph shape for filament lamp (2 marks)
- Explain why resistance changes with temperature (3 marks)
- Required practical: method and control variables (4 marks)
- State and explain how a thermistor/LDR works (2 marks)
📝 Key Command Words:
- Calculate — show V = IR substitution with units
- Describe — say what the graph looks like (shape, gradient)
- Explain — say why (use "because" with ion vibration)
- Sketch — draw a labelled graph (axes, origin, shape)
⚠️ Common Mistakes to Avoid:
- Forgetting units for resistance (Ω, not R)
- Saying metal resistance decreases with temperature — it increases
- Confusing thermistor (less R when hot) with metal wires (more R when hot)
- Drawing filament lamp V-I graph as a straight line — it curves
- Not turning off the power supply between readings in required practical
Quick Check: A thermistor is placed in ice water, then hot water. What happens to its resistance, and how does this affect current in the circuit?
In ice water: resistance is high, so current is low. In hot water: resistance decreases, so current increases. Thermistors have resistance that decreases as temperature increases.
Practice questions for Resistance & Ohm's Law
Which of the following best describes electrical resistance?
Explain what is meant by an ohmic conductor.