Thermometer. Definition and application

Feelings of warmth, coolness, hot and cold - are subjective feelings. Without thermometers, we would not be able to precisely determine the temperature of bodies, air or water. How do thermometers work and what are their types?

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1. Thermometer. Definition

The thermometer is a measuring instrument for determining temperature by an indirect method. Its basis is the influence of temperature changes on the properties of bodies with specific characteristics, in which these changes are constant and possible to measure and refer to the scale. They are called thermometric properties.

Thanks to thermometers, we can measure the temperature of the environment or specific objects. Thermometers are used to measure temperatures up to 600 ° C. Measuring instruments for higher temperatures are called pyrometers.

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2. Types of thermometers

Thermometers can be divided according to the principle of operation. Here are the most common types of thermometers:

  • Liquid thermometers - the most commonly used. They use the phenomenon of thermal expansion of the liquid. Most often it is mercury or alcohol.
  • Mercury thermometers enable temperature measurements from -38 ° C to +356 ° C. On the other hand, alcohol from -70 to +120 ° C.
  • Gas thermometers - as the name implies, the working medium is gas. Gas parameters are measured, e.g. volume at constant pressure or pressure at constant volume.
  • Steam thermometers - they use the dependence of the pressure of saturated steam on its temperature. They are often used in car thermostats.
  • Resistance thermometers - they are based on the dependence of the electric current resistance on the temperature of the current conductor, where cables made of platinum and special alloys are usually used.
  • Magnetic thermometers make use of the close relationship between the magnetic susceptibility (susceptibility to magnetization) of certain substances and their temperature. They are very useful in certain technical fields as they also allow the measurement of near temperatures.

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3. Thermometers. Application

Thermometers are classified by application. High-precision medical thermometers are used in medicine to measure body temperature.

The range of medical thermometers is from 35 to 42 ° C. The most common are mercury thermometers, or more often - electronic ones, which work by sensing waves of infrared radiation.

In science, laboratory thermometers are used to measure the temperature of various substances, usually placed inside glass apparatus. Laboratory thermometers look quite similar to medical thermometers, only they are usually longer. The measurement scale is from 0 to 150 ° C.

4. Temperature scales. Kelvin

There are three main scales for measuring temperature in the world - Kelvin, Celsius and Fahrenheit.

In scientific applications, the Kelvin scale is most often used, denoted by the letter K. It was created in 1848 by the Scottish physicist William Thomson, Lord Kelvin.

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The Kelvin scale begins at the point of the lowest possible temperature at which the movement or bonding of body molecules stops. A temperature of 0 K equals a temperature of -273.15 ° C.

The kelvin is also the basic unit of temperature in the SI or International System of Units. Contrary to the popular Celsius scale, the Kelvin scale does not use the term "degrees", but Kelvin.

## Temperature scales. Celsius

The most common temperature scale in the world is the Celsius scale, where temperatures are given in degrees Celsius and denoted by the ° C sign.

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The Celsius scale is based on two fixed points: 0 ° C (melting point of ice) and 100 ° C (boiling point of water). The temperature unit is the degree Celsius (° C).

## Temperature scales. Fahrenheit

In some Anglo-Saxon countries (e.g. in the United States) the temperature is expressed on the Fahrenheit scale, where 0 is shifted from the zero Celsius scale by 32.

32 ° F correspond to the melting point of ice and 212 ° F to the boiling point of water at normal pressure, i.e. 1013 hPa.

The unit of the Fahrenheit scale is the degree Fahrenheit, denoted as ° F.

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