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.
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
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.
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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