Types Of Thermometer In Physics

Types of Thermometer In Physics-Thermometer is the instrument that is used to measure temperature. The name was gotten from two Greek words “thermos” which means “hot” and “metron” which means “measure”.

This tool allows you to measure the temperature of anything. A lot of people do use temperature and heat interchangeably but these two terms do not mean the same thing.

Temperature is the degree of hotness or coldness of an object. In a more simplified form, we would say temperature is how hot or cold an object is. Heat on the other hand is a form of energy and it is the how hot an object is.

So how do we measure the temperature of an object? How do we know how hot or cold an object is? This is the work of a thermometer.

In this article, we will be looking at how the types of thermometers, where they are used and how you can use them.

Before proceed, let’s talk briefly on thermometer and temperature.

We said in one of the paragraphs above that temperature is the degree of hotness or coldness of an object. There are different units that are used to measure temperature and they are Celsius (oC), Kelvin (K) and Fahrenheit (oF).

So the different types of thermometer measures temperature using any of the units of measurement.

Thermometer Fluid

This is the liquid that is inside the thermometer and it must be visible to tell the temperature during measurement. The freezing point of the liquid must be low and the thermal expansion of the liquid must be uniform.

It should have a high boiling point and should be a good conductor of heat. The liquid should not wet glass and also have a small specific heat capacity.

Types Of Thermometer

There are different types of thermometer used for measuring temperature and they are:

  • Alcohol in glass thermometer
  • Clinical or medical thermometer
  • Constant pressure gas thermometer
  • Constant volume thermometer
  • Digital thermometer
  • Infrared thermometer
  • Laboratory thermometer
  • Mercury thermometer
  • Platinum resistance thermometer
  • Pyrometer thermometer
  • Thermocouple thermometer

Alcohol in glass thermometer

This thermometer is made of sealed glass and it shows the temperature by the level at which mercury or alcohol reaches a graduated scale. Temperature here is indicated by the changes in liquid.

Thermometer features colored alcohol that is less toxic unlike the mercury in glass thermometer. It is sometimes called spirit thermometer.

The ethanol version is the most used type of alcohol in glass thermometer because of its low cost and also low hazard of the liquid in event of breakage.

The ethanol-filled thermometer has upper limit measurement of 78oC (172.4oF) which makes it to be more useful for daytime, nighttime and body temperatures.

Clinical thermometers

The clinical thermometers are also called the medical thermometers and they are meant for clinical purposes. They are used for measuring the human body temperature.

It is a narrow glass tube with a bulb containing mercury at the end. The clinical thermometer has a range between 35oC to 42oC and the normal human body temperature is 37oC although it can fluctuate between 35oC to 42oC which makes the clinical thermometer suitable for measurement.

The level of the mercury in the thermometer tells the body temperature although mercury is a toxic element.

The clinical thermometer must be sterilized before use.

How to use a clinical thermometer

  • Wash the thermometer with water at a normal temperature
  • Make sure the mercury level of the thermometer falls down below the 37oC mark or the 98oF mark which is the normal body temperature.
  • Put the thermometer under the tongue or under the arms in order to get the reading on the thermometer
  • Look at the thermometer closely to get the correct reading
  • The temperature different indicated between the two bigger marks should be noted
  • Note the value of the bigger mark that the mercury thread has crossed

Laboratory thermometer

This thermometer is used to measure temperature of other objects that the clinical thermometer cannot measure. It is colloquially known as the lab thermometer and it ranges from -10oC to 110oC.


The laboratory thermometers are designed to check the boiling point, freezing point or temperature of other substances in the lab or during experiments.

The thermometer can be used for checking the temperature of a solvent.

Digital thermometer

This thermometer is used to measure temperature using an electric circuit. The information captured is sent to a microchip that processes it and then it displays it numerically on the digital screen.

The digital thermometer is easy to use, accurate and less expensive. Since the mercury in glass thermometer contain mercury which is toxic, the digital thermometers have been used to replace them in clinics as they are considered to be more advanced in measuring body temperature.

How to use the digital thermometer

  • Turn on the thermometer and click till the number zero appears on the screen
  • Place the tip of the thermometer under the armpit
  • Wait for a while before you hear the alarm from the thermometer
  • Remove the thermometer and check for the temperature on the display
  • Clean the tip of the thermometer with cotton and alcohol after use.

Infrared Ear Thermometer

The tympanic membrane temperature is the process of using the inside of the ear to check the body temperature. It is more common when checking the temperature of children.

The infrared thermometer measures the temperature in form of infrared energy given off by the heat source. The normal ear temperature in adults is 37.5oC.

How to use the infrared ear thermometer

  • The tip of the thermometer should be placed inside the ear pointing towards the nose
  • Press the power button on the thermometer until a signal is heard
  • Read the temperature value
  • Remove the thermometer from the ear and clean the tip with cotton and alcohol.
  • When using this thermometer, ensure that the ear is not containing a lot of wax.

Mercury thermometer

This thermometer were the first types of thermometer but it has been replaced by more efficient thermometers as a result of mercury which is a toxic liquid that is poisonous to the hazard.

Mercury thermometer is used to provide accurate temperature readings and it is used to measure the temperature under the arm, orally or rectally.

Constant Pressure Gas thermometer

This thermometer can function at constant pressure and also volume conditions.

This type of thermometer offers highly accurate measurement and is used to adjust other thermometers.

Constant Volume Gas thermometer

This thermometer is used to measure temperature and when the temperature increases, the pressure increases. It measure temperature in the range 0k to 500k.

Platinum Resistance thermometer

This thermometer uses a platinum wire that is attached to an electrical resistance.  The thermometer is used to measure outside temperature and it is slow but offers accurate readings.

When the temperature increases, the resistance in the thermometer increases and it measures temperature in the range of 500k to 2300k.

Pyrometer thermometer

This particular thermometer operates on the Stefan’s law. The thermometer measures the temperature from the heat radiation emitted by the objects.

One uniqueness of the pyrometer thermometer is that it can be used without being in contact with the object to measure. It measures temperature greater than 2000k.

Thermocouple thermometer

This is used for quick measurement of temperature. It is used mostly in laboratories. The thermometer uses an electrical resistance to generate a voltage that varies according to the connection temperature. It measures temperature in the range of 500k to 2300k.

Frequently Asked Questions

How do you know if a thermometer is accurate?

For you to know if a thermometer is accurate, you will need to insert the stem of the thermometer in the ice water in a way that the stem is at least an inch deep without touching the glass.

Then you wait for a while so that the thermometer gets the reading of the ice water. If the thermometer reading is 0oC or 32oF, then the thermometer is said to be accurate.

Who is the father of thermometer?

The father of thermometer is Daniel Gabriel Fahrenheit and he was a German physicist who dedicated his life to science and inventions.

Which liquid are used in a glass thermometer?

The major liquids that are used in glass thermometers are mercury and alcohol but mercury are now being replaced by alcohol as a result of its toxic nature which poses danger on human health.



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