Thermometer is a device for measuring temperature by indirect method, on the basis of changes in thermometric properties of the thermometric body used in the thermometer. The range of measured temperatures and applications of the thermometer depends to a large extent on the thermometric body and thermometric properties. The thermometer can be used to measure any temperature in a specified range or to indicate only selected temperature values (temperature indicators).

How does thermometer work?

What thermometers measure is actually the momentary kinetic energy of the air particles adjacent to the thermometer. Air molecules move more slowly in cooler air than in warmer air – the kinetic energy of air molecules is directly proportional to the square of the speed at which they move. As a result, colder air is characterized by less kinetic energy. When these molecules encounter a thermometer post in their path, their kinetic energy is transferred to the glass and then to the mercury particles (alcohol) contained in the thermometer, mercury molecules start to move faster and move further (higher). When the air cools down, the kinetic energy transferred to the molecules of the fluid filling the thermometer decreases – these molecules slow down and as a result the level pointed by the mercury or alcohol bars decreases.


Measuring the air temperature with a thermometer is all well known.

What really makes the thermometer show this and not the other temperature?

Window thermometers overheat the temperature due to heating the window pane. Electronic thermometers on the streets often indicate the temperature in partial shade or even in the light sun, which is why they also overstate the value.
The biggest mistake that, contrary to what you might think, is committing a lot of people, is to measure the temperature of the air in the full sun, for example, a window thermometer alcohol.
No man has yet been able to determine what temperature really prevails in the sun, because the result is falsified by heating the thermometer itself. So if we measure the temperature in the sun, we do not get the temperature of the air, but the temperature of the thermometer, which is completely useless.
Therefore, according to meteorological standards, the temperature in the full glare of the sun is not measured, at least it does not inform about it. All data provided in weather forecasts in the media are, of course, temperatures in the shade. In the full sun it is usually a dozen or so degrees warmer, depending on what the weather is.

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