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Thermometers
Beginner
Devices using thermal expansion or electrical change.
Thermometers use a property that changes with temperature: liquid expansion, bimetal bending, electrical resistance (RTD, thermistor), thermocouple voltage or infrared emission.
Clinical thermometers use mercury-free alcohol or digital sensors.
Calibrate at two fixed points.
In more detail
Thermometers work by using a property that changes with temperature, such as the length of a liquid column, electrical resistance or the colour of a material.
Real-world uses
- Clinical thermometers measure body temperature.
- Infrared thermometers measure surface temperature without contact.
- A mercury or alcohol thermometer works because the liquid expands as it warms, rising up a narrow tube.
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Frequently asked questions
Why do thermometers take time to settle?
Heat must flow between the thermometer and the object until they reach thermal equilibrium.
How accurate are thermometers?
Depends on calibration. Good ones are accurate to a fraction of a degree.
How does a digital thermometer work?
It uses a sensor whose electrical resistance or voltage changes with temperature, which is then converted into a reading.
Related topics in Heat & Thermodynamics
Temperature · Temperature scales · Zeroth law · Thermal expansion · Area and volume expansion