How does a thermometer work?

We all have used thermometers at some point of time or the other but have you ever wondered what is the actual working procedure of the thermometer whether you are using the electric thermometer or whether you are planning to use a old school thermometer like a mercury thermometer.

We all like to measure the temperature on a daily basis especially on the days when there is a large amount of fluctuation in the temperature but have you ever wondered what actually happens inside the thermometer so that you are able to know the exact temperature.

The working of different thermometers is completely different and that is why when we are speaking about the working of the thermometers we would be speaking about them according to the type of thermometers we are discussing so that we can individually discuss about the working of each type of thermometer.

Mercury thermometers:

These are the most old school type of thermometers which are available and they are hardly being used these days because the other ones are much more easier to manage and use. With that being said if you want to see the actual working of the thermometer while you’re measuring the temperature then these are the best options which you have.

If you look at these thermometers there is a small capital of the tube running in the centre of the thermometer and around it temperature scale is kept to let you know about the temperature which is they are currently and this temperature scale is already marked with the entire range of temperature and in most of the cases the one side of the scale consist of the centigrade and the other side of the scale consist of the Fahrenheit which are both units of temperature.

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The central capillary tube consists of mercury and the expansion and the contradiction of mercury with respect to the temperature is taken into account to measure the temperature which is being measured.
mercury thermometer
At the normal day to day temperatures you would find that mercury is entirely liquid and therefore any contradiction are expansion can be easily noticed. As the temperature increases mercury expounds and since the only space for it to expand is in the capillary tube the mercury level rises in that you and therefore this also corresponds with the temperature scale which is placed on both sides of the capillary tube.

All it takes for the mercury to expand are a few seconds and based on the level which it freezes after that period of time you can easily see the marking in the scale which is beside the capillary tube and understand what is the temperature currently which you are measuring.

The thermometer which is based on mercury would be able to provide you with exact readings only when it is calibrated properly and for that it is taken into consideration the boiling point as well as the freezing point of water because water boils at 100°C and it freezes at 0°C and therefore when water is in these conditions the thermometer is dipped into the water and the mercury level rises are falls accordingly and the markings are made on the scale which is beside the capillary tube. And accordingly the other points are marked as well and thus we have a completely working thermometer.

Dial thermometer:

dial thermometer

Mercury-based thermometers are not the only options for the thermometers which you have and you also have the option of dial thermometers which do not work on the basis of mercury.

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Dial thermometers have a coil inside it which expands or contracts depending on the temperature which the thermometer is exposed to and this metallic coil then mows the point at which indicates the temperature. The calibration method of the dial thermometer is also the same as that of mercury-based thermometer.

Electric thermometers:

electric thermometer

The main issue with the mercury thermometer and the dial thermometer is that they are needed to be subjected to the temperature which you are measuring for a longer period of time for them to show the accurate reading but when you’re speaking about the electric thermometer you would realise that the electric thermometer can almost as instantaneously provide you with the temperature which you are measuring.

This makes the electric thermometer one of the fastest types of thermometers which is present these days. With that being said the question which remains is that how does a electric thermometer work?

Electric thermometer consist of a piece of metal through which electricity is passed and the resistance to the passage of electricity is dependent on the temperature of this metal because of the temperature of the metal increases beyond a certain level then the atoms in the thermometer start vibrating and therefore this hampers the moment of electricity because the resistance increases.

As the temperature of the metal goes down electricity is again able to move quite freely.

Since the amount of electricity which is passed through this metal is always constant and the resistance is wearing depending on the current which reaches the other end of the metal the temperature which the thermometer is subjected to can be instantaneously calculated and this is displayed in the display of the thermometer. All this is done with the help of a microchip which is present in the thermometer and since this entire process is done in a few microseconds, the electric thermometer does not take a lot of time to display the temperature which you want to read.

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It has also been seen that the electric thermometer is actually much more sturdy and much more compact as well and that is why the other types of thermometers are actually being replaced by the electric thermometer because of its high efficiency and because of its compact and portable nature.

Calibration of thermometer:

calibrating a mercury thermometer

When you’re speaking about the mercury-based thermometer many people have actually asked regarding how this thermometer is calibrated because if there is any problem in the calibration of the thermometers than the readings which are shown by the thermometer would also not be proper.

The easiest way for the calibration of the thermometer is to just put the mercury in the capillary tube and dip the thermometer into boiling water because the boiling point of water is 100°C and therefore when you dip the thermometer in boiling water and the level to which mercury rises can be marked as 100°C and similarly the freezing point of water is 0°C and in the same way when you put the thermometer in freezing water that is when it is just getting converted to ice you can get the 0°C temperature as well and you can market on the scale.

Now that you have these two reference points for measuring the temperature you can calculate the other calibrations on the scales accordingly as well. This is how the calibration of the thermometer is done.