LDRs and thermistors
I can describe how an LDR or a thermistor can be used in a sensing circuit.
LDRs and thermistors
I can describe how an LDR or a thermistor can be used in a sensing circuit.
Lesson details
Key learning points
- An LDR is made of a semiconductor, and the brighter the light shining on it, the lower its resistance.
- Light transfers energy that enables electrons in a semiconductor to move as they do in a metal conductor.
- A thermistor is made of a semiconductor, and the hotter it is, the lower its resistance.
- Heating transfers energy that enables electrons in a semiconductor to move as they do in a metal conductor.
- A potential divider circuit can be set up with an LDR/thermistor to trigger a switch if it becomes too dark or too cold.
Common misconception
Circuits are analysed sequentially, starting at the battery and working round, one component at a time.
Ask questions that prompt pupils to consider the effect of changes to one component on the whole circuit.
Keywords
Light-dependent resistor - a semiconducting component with a resistance that gets lower in increasingly bright light
Semiconductor - a material that has both metallic and non-metallic properties
Thermistor - a semiconducting component with a resistance that gets lower in increasingly high temperatures
Potential divider - a series circuit that divides the p.d. across a power supply into two or more smaller voltages
Equipment
LDRs, thermistors, ohmmeters (multimeters set to resistance measurement), electrical leads, crocodile clips, beakers, thermometers, kettle for heating water
Content guidance
- Risk assessment required - equipment
Supervision
Adult supervision required
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
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