IGCSE Physics: Thermistors and LDRs | Edexcel Modular | Unit 2 | L5

IGCSE Physics: Thermistors and LDRs | Edexcel Modular | Unit 2 | L5

This lesson covers spec point 2.11 — describing how the resistance of a
thermistor changes with temperature and how the resistance of an LDR changes
with light intensity, and applying this understanding to circuit contexts.

PowerPoint includes:
• Retrieval starter reviewing V = IR and resistance from L3
• Direct Instruction (I Do) — thermistor defined; resistance–temperature
relationship stated; LDR defined; resistance–light intensity relationship
stated; both contrasted with metal wire behaviour; applications introduced
(fire alarms, automatic lighting, temperature sensors)
• Guided Practice (We Do) — state how resistance changes in given scenarios;
explain what happens to the current in a series circuit containing a
thermistor when temperature changes; identify a suitable component for a
given application
• Independent Practice (You Do) — thermistor and LDR application questions;
explain responses using V = IR; suggest and justify component choices
• Review and Reflect — 3 MCQs and exit ticket

Activity Sheet includes:
• Circuit diagram of thermistor, lamp and battery in series (for Q8)
• 10 exam-style questions covering thermistor and LDR behaviour, applications
and circuit calculations using V = IR
• Stretch question: LDR in series with a fixed resistor — calculate current in
bright and dim light and explain the effect on voltage sharing
• Full mark scheme for teacher use