thermometers

A thermometer is a device used to measure temperature. It operates by relying on a physical property that changes predictably with temperature, such as liquid expansion, electrical resistance, or infrared radiation. Thermometers are used across science, medicine, industry, and everyday life.

Liquid-in-glass thermometers contain a sealed liquid, typically mercury or alcohol, that expands and contracts in a narrow capillary as temperature changes. Bimetallic strip thermometers use two metals with different expansion rates that bend with temperature. Electronic thermometers measure temperature with sensors such as thermistors or resistance temperature detectors (RTDs). Thermocouples generate a voltage proportional to temperature difference. Some devices combine these principles within digital readouts.

Infrared thermometers sense infrared radiation emitted by objects and convert it to a temperature reading, allowing non-contact measurements. Probes and sensors can be designed for oral, rectal, aural, or skin contact in medical use, and industrial temperature monitoring.

History: early temperature measurement began with thermoscopes in ancient and medieval times. The Fahrenheit and Celsius scales were developed in the 18th century and standardized later for widespread use, enabling consistent thermometry across regions and disciplines.

Calibration and accuracy: thermometers require calibration against known reference temperatures and appropriate adjustment for environmental conditions. Medical thermometers aim for precise readings within fractions of a degree Celsius; industrial devices emphasize stability over time and resistance to process conditions.

Safety and disposal: mercury-containing thermometers are restricted in many regions due to mercury toxicity; many jurisdictions promote alcohol-based or digital alternatives and proper disposal of devices to prevent mercury release.

Applications include medical thermometry, meteorology, food safety, and industrial process control.