What is a Thermometer and How Does It Work

We can now safely say that humanity has come far enough to quantify virtually everything and give units to all kinds of measurements. With this establishment, a multitude of inventions has ensured that these quantities and their precise figures can be drawn by anybody, be it professional or personal purpose.

One of the most important and significantly measured components is temperature. At least once your body or forehead seemed to get hotter, you must have had your temperature checked by your mother once using a thermometer. Why does the body temperature measured by a thermometer? Can a thermometer only measure the body temperature of a person to detect fever? This seems to be the general and the most miscomprehended idea.

how does a thermometer work

How Does a Thermometer Work

Thermometers are of various types; each has its unique functionality and application. However, its fundamental objective remains the same, which is to measure the temperature. If anyone is showing the signs of fever, you measure their temperature, and the more the temperature, the worse the condition.

Once you know the temperature, you can pursue the necessary course of action to treat the ailing person. If the person is suffering from mild fever, it can be treated right at home with no scrupulous supervision. But the temperature is higher than what is perceived as "mild", the person may need immediate medical attention from professionals. Thus, you can know a lot about a person's condition by just reading his or her temperature.

Not only can it give you a brief assessment of a body, but several other kinds of thermometer can give you the necessary intel to assist you in your due course. Since the types of each thermometer are at variance, naturally, their application, objective, functionality will be different too. In this article, we will discuss each of the prominent type and widely used thermometers as well as their application and operation.

Working of Liquid thermometer:

One of the most basic thermometers is the liquid thermometer. As the name suggests, it can measure the temperature of any liquid and distinguish them on the basis of it. It has a very simple and basic design.

A liquid thermometer consists of a thin glass tube fitted inside a scale for the purpose of reading temperature and filled with a small quantity of silver liquid. This liquid is mercury. Mercury is an extremely toxic element, and its special characteristics include that even though it’s a metallic element, you will find it in the form of liquid at room temperature. 

Due to thermal expansion, the mercury increases when it becomes hotter proportionately to the temperature of the liquid under observation. The glass, fitted in the scale, allows you to read the temperature by observing how much the mercury has risen. Most liquid thermometers come with both scales of measurement, namely, Celsius and Fahrenheit.

However, it's not necessary that the thermometer may have mercury as its center-piece. Nowadays, mercury is being replaced by alcohol-based liquids, for instance, ethanol due to the high toxicity of the mercury. Even though it is not harmful as long as it is in the confinement of the thermometer, it is still dangerous because of the potential event of the glass breaking and exposing the toxic substance to its surroundings.

One way to distinguish whether your thermometer has mercury or alcohol is through the color of the liquid. If the liquid is silver, the substance sustaining the device is mercury. On the other hand, if the substance is red, the substance is alcohol. 

Working of Dial Thermometer:

The fundamental idea in the Dial Thermometer is more or less similar to that of the liquid or any thermometer. For that matter, the metallic strip expands as it gets hotter and points towards the accurate figure. The difference is in the design.

While you have a long glass tube in case of a liquid thermometer (a design that facilitates the process of taking the measurement of a liquid), dial thermometers have a circular shape, and the pointer inside is mounted on a bimetallic strip that expands as it gets hotter.

The bimetallic strip will expand corresponding to the temperature of the subject under observation and give you the measurement accordingly.

Working of Forehead Thermometer:

Forehead thermometer is a specialized thermometer which is generally made exclusively for the detection of fever by taking the measurement of the forehead. These thermometers have a highly comprehensive design and have undergone much change. 

Since they are widely used to take the temperatures of babies and young kids, they do not possess mercury as they are digital. They also facilitate no contact operation wherein all you have to do is take the thermometer close to the forehead of the baby with just a distance of 1 inch between them, and the measurement will appear on the screen.

It is ideal to take the temperature of sleeping babies as it does not cause discomfort and disturb their sound sleep. Apart from taking the temperature of the forehead, you can also take the temperatures of liquids, objects, room, etc. Even though it may not work as accurately against these components as against the body, you will get a rough idea to the least.

Working of Electronic Thermometer: 

Electronic thermometers are lauded for their quickness, something you would not find in mechanical thermometers like liquid and the dial thermometers. It comes with a comprehensive display, which makes the reading all the more convenient.

Instead of the good old taking the temperature and waiting for results, an electronic thermometer has a way with swiftness by just coming in contact with the object whose temperature requires to be measured, and in just a matter of seconds, the results will appear on the screen.

The functionality of the electronic thermometer is based on the resistance of the metal. With the increase in the temperature of the metal, subsequently, the resistance augments. The distinctive feature of the electronic thermometer that enables it to be ahead is its quickness in reading temperature, which is absent in the rest.


Thermometers undoubtedly are a great creation of man. From making comprehensive reports on various things from taking mere body temperature, you can get a lot done through the means of a thermometer. These are some of the most general thermometers in existence, apart from these, there are several different thermometers which aids men in their research and dissemination under the classification of these broad categories. I hope this article rendered the information you were looking for.

They gather information about these particulars and relay it to the masses. But how do they measure it? The enhanced technology has enabled the human race to virtually know about everything and anything under the sun. For measuring the components of weather, a specialized device, namely, an anemometer is used.

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About the Author


I am Tim, a weather enthusiast who loves to watch hurricanes and all other harsh weather conditions. I studied B.Sc(Meteorology) at the University of Miami. With excellent knowledge of Weather Forecasting, Meteorology, and Environmental Science, I am currently working in San Francisco as a Meteorologist. Also, I am a member of The Weather Channel and AccuWeather. In this blog, I will write a detailed review of Weather instruments that you need for survival and other activities.