1. Liquid-in-glass thermometers:
* How it works: These thermometers contain a liquid (usually mercury or alcohol) that expands as it gets warmer and contracts as it cools. The liquid is sealed inside a glass tube with a scale marked on it. As the liquid expands, it rises up the tube, indicating the temperature.
* Why it works: Liquids have a property called thermal expansion, meaning they change in volume (size) when their temperature changes. This change in volume is directly proportional to the temperature change, allowing us to use the liquid's expansion to measure temperature.
2. Digital thermometers:
* How it works: Digital thermometers contain a thermistor (a temperature-sensitive resistor). When the thermistor heats up, its electrical resistance changes. The thermometer measures this change in resistance and converts it to a temperature reading, displaying it on a digital screen.
* Why it works: Thermistors are made from materials whose electrical resistance changes significantly with temperature. This change in resistance can be accurately measured and related to the temperature change.
3. Infrared thermometers (ear or forehead thermometers):
* How it works: These thermometers measure the infrared radiation emitted by an object. The amount of infrared radiation emitted depends on the object's temperature.
* Why it works: All objects with a temperature above absolute zero emit infrared radiation. The intensity of this radiation increases with temperature. Infrared thermometers measure this intensity and convert it to a temperature reading.
4. Thermocouples:
* How it works: Thermocouples consist of two different metal wires joined at one end. When the junction is heated, a voltage is generated. This voltage is proportional to the temperature difference between the junction and the other end of the wires.
* Why it works: Different metals have different electrical properties. This difference causes a voltage to be generated when the junction of two dissimilar metals is heated. This voltage is directly proportional to the temperature difference, allowing the thermocouple to measure temperature.
In summary, thermometers work by measuring a physical property (volume, electrical resistance, infrared radiation, or voltage) that changes predictably with temperature. This change is then converted into a temperature reading.
