thermometer
-
What is a thermometer?
A thermometer is an instrument used for measuring the temperature of a system. The first thermometer is generally credited to Galileo Galilei around 1592. It consisted of a glass vessel that would expand or contract air inside of it based on the changing temperature.
Many substances that change with temperature alterations can be the basic component of a thermometer. Liquid thermometers were once the most common type. In the 21st century, digital thermometers have risen in popularity due to their accuracy and the absence of toxic mercury. Other types of thermometers include gas thermometers, electrical resistance thermometers, thermocouples, and bimetallic strip thermometers.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What does a thermometer measure?
A thermometer is an instrument that measures the temperature of a system. It relies on the principle that a substance changes with alterations in its temperature.
Several temperature scales exist, including Fahrenheit (\u00b0F), Celsius (\u00b0C), and Kelvin (K), the international standard for scientific temperature measurement. The Rankine scale (\u00b0R) is used in some engineering fields, while the Rèaumur scale (\u00b0Re) formerly saw use in Europe.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does a basic thermometer work?
A thermometer measures the temperature of a system, which is important in manufacturing, research, and medicine. The basic principle behind many thermometers involves using a substance that changes in some way when its temperature changes.
Liquid thermometers, once very common, use mercury or colored alcohol in a glass tube; the liquid's expansion or contraction indicates temperature. Bimetallic strip thermometers use two different metals bonded together; when heated, the metals expand at different rates, bending the strip and indicating temperature change. Digital thermometers use a thermistor, a resistor whose resistance varies with temperature.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some different types of thermometers?
Thermometers measure temperature using materials that change with temperature variations. Several types exist:
- Liquid Thermometers: These used to be common and contained mercury or colored alcohol in a glass tube.
- Digital Thermometers: These replaced mercury thermometers for greater accuracy and safety, using a thermistor, a resistor that responds to temperature.
- Infrared Thermometers: These focus infrared light onto a detector, which measures the light and converts it into a temperature reading.
- Electrical-Resistance Thermometers: Typically using platinum, these measure temperature based on the principle that electrical resistance changes with temperature.
- Thermocouples: These industrial thermometers use two wires of different materials joined at one end. Temperature differences between the ends create a voltage, indicating temperature.
- Bimetallic Strip Thermometers: Durable thermometers using two bonded metal strips that expand at different rates when heated, causing a bending effect to measure temperature change.
5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do digital thermometers differ from traditional ones?
Digital thermometers have replaced traditional liquid thermometers because they are more accurate and do not contain toxic mercury. Traditional thermometers use liquid, typically mercury or colored alcohol, sealed in a glass tube, whereas digital thermometers use a thermistor, a resistor that reacts to temperature changes. Digital thermometers may also use infrared technology to measure temperature.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Where are thermometers commonly used in everyday life?
Thermometers are commonly used to measure temperature in manufacturing, scientific research, and medical practice. Liquid thermometers, once the most common type, have been replaced by more accurate electronic digital thermometers in the 21st century. Digital thermometers often use a thermistor, a resistor with a resistance that varies with temperature. Infrared thermometers are also used to measure body temperature. In industry, thermocouples are among the most widely used thermometers.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
thermometer, instrument for measuring the temperature of a system. Temperature measurement is important to a wide range of activities, including manufacturing, scientific research, and medical practice.
The invention of the thermometer is generally credited to the Italian mathematician-physicist Galileo Galilei. In his instrument, built about 1592, the changing temperature of an inverted glass vessel produced an expansion or contraction of the air within it, which in turn changed the level of the liquid with which the vessel’s long, open-mouthed neck was partially filled. This general principle was perfected in succeeding years by experimenting with liquids such as mercury and by providing a scale to measure the expansion and contraction brought about in such liquids by rising and falling temperatures.
By the early 18th century as many as 35 different temperature scales had been devised. The German physicist Daniel Gabriel Fahrenheit in 1700–30 produced accurate mercury thermometers calibrated to a standard scale that ranged from 32°, the melting point of ice, to 96° for body temperature. The unit of temperature (degree) on the Fahrenheit temperature scale is 1/180 of the difference between the boiling (212°) and freezing points of water. The first centigrade scale (made up of 100 degrees) is attributed to the Swedish astronomer Anders Celsius, who developed it in 1742. Celsius used 0° for the boiling point of water and 100° for the melting point of snow. This was later inverted to put 0° on the cold end and 100° on the hot end, and in that form it gained widespread use. It was known simply as the centigrade scale until in 1948 the name was changed to the Celsius temperature scale. In 1848 the British physicist William Thomson (later Lord Kelvin) proposed a system that used the degree Celsius but was keyed to absolute zero (−273.15 °C); the unit of this scale is now known as the kelvin. The Rankine scale (see William Rankine) employs the Fahrenheit degree keyed to absolute zero (−459.67 °F).
" height="20" alt="HEW Logo">
Any substance that somehow changes with alterations in its temperature can be used as the basic component in a thermometer. Gas thermometers work best at very low temperatures. Liquid thermometers were once the most common type in use. They were simple, inexpensive, long-lasting, and able to measure a wide temperature span. The liquid was almost always mercury or coloured alcohol, sealed in a glass tube with a gas like nitrogen or argon making up the rest of the volume of the tube. In the early 21st century, mercury thermometers were supplanted by electronic digital thermometers, which were more accurate and did not contain toxic mercury. Digital thermometers use a thermistor, a resistor with a resistance that varies with temperature. To measure body temperature, infrared thermometers that focus infrared light onto a detector that measures the amount of light received and convert the electrical signal produced by the detector into a temperature were also used.
Electrical-resistance thermometers characteristically use platinum and, like thermistors, operate on the principle that electrical resistance varies with changes in temperature. However, they can measure a much greater temperature range than thermistors. Thermocouples are among the most widely used industrial thermometers. They are composed of two wires made of different materials joined together at one end and connected to a voltage-measuring device at the other. A temperature difference between the two ends creates a voltage that can be measured and translated into a measure of the temperature of the junction end. The bimetallic strip constitutes one of the most trouble-free and durable thermometers. It is simply two strips of different metals bonded together and held at one end. When heated, the two strips expand at different rates, resulting in a bending effect that is used to measure the temperature change. Thermostats formerly used bimetallic strips as temperature sensors, but modern digital thermostats use thermistors.
Other thermometers operate by sensing sound waves or magnetic conditions associated with temperature changes. Magnetic thermometers increase in efficiency as temperature decreases, which makes them extremely useful in measuring very low temperatures with precision. Temperatures can also be mapped, using a technique called thermography that provides a graphic or visual representation of the temperature conditions on the surface of an object or land area.