Thermometer Reading Temperature



Thermal energy is a form of energy which generates due to heat and flows from the higher amount of temperature to the lower amount of temperature in the body on contact. It is possible to measure the thermal energy in the body with the utilisation of the "sum of kinetic energies".

"Joule" (J) is the SI unit of the heat energy and Calorie is the practical unit of the "heat energy" (Aw, 2020).

Hence, the hotness and coldness of the body are the temperatures, where a thermometer can measure the temperature of the body.

About Thermometer

A reliable medical instrument requires keeping measuring the temperature of the body. Thermometers are essentially constructed by containing alcohol or mercury inside a glass tube. On the body of the tube, different marks are assigned regarding the temperature with different scales such as "Celsius" and "Fahrenheit".

The expression of temperature captured by the thermometer is expressed with the degree Celsius or Fahrenheit.

The growth of mercury due to warmth is the temperature of a body. The temperature distinction is the indication of the different marks that are available on the glass front of a thermometer.

Figure 1: Glass Thermometer

Process of measuring the body temperature with a thermometer

The thermometer is the only medical instrument that is trusted and operated by a major number of people to measure body temperature. It can deliver accurate temperature readings of a human or animal body. Although, there is a different process that needs to be followed while measuring temperature.

A used thermometer needs washing with water at normal temperature before use. One needs to give a few jerks before using the thermometer which can bring the level of mercury down in the glass.

The mercury level beneath the mark of "37°C or at 98°F" is the ideal situation to mark the body temperature (Chen, Chen & Chen, 2020).

Additionally, When the temperature is kept constant, the ideal "pressure (p) and volume (v)" of a portion of gas are connected as "PV = constant".

Types of Thermometers to read the temperature

Different types of thermometers are available as medical equipment that are used for both household and laboratory purposes to measure the temperature. The followings are the different types of thermometers available for different purposes:

Digital and electrical thermometers

Currently, the digital thermometer is the quickest and the finest procedure to measure body temperature.

The "electrical resistance" placed inside the electrical or digital thermometer changes with the attraction of any changes in temperature, heat or cold. This thermometer is usually powered by batteries and delivers results that are more accurate in any situation. On the other hand, the electrical thermometers use "platinum and, thermistors", which operate on the principle that "electrical resistance" alters with temperature differences. Regardless, the "electrical thermometer" can calculate a much more remarkable temperature field than "thermistors".

Use of digital thermometers to read temperatures

The followings are the specific types of "digital thermometers" that are used in different ways:


This method is useful for an infant who is 4 years old and can hold the thermometer in their mouth for a minute. In this process, placing the thermometer under the tongue delivers accurate reading.


Babies that are under 3 years old are taken for this method to measure body temperature. A thermometer can insert into babies rectum is followed to measure temperature.


In this process, the thermometer can be placed at a child’s armpit to get the temperature reading. This process takes time usually considered to the oral process.

"Tympanic (ear)"

The application of the infrared light to measure the heat is followed in the Tympanic thermometer. This type of thermometer delivers the reading in the fastest way compared to the other types (Fajrin et al. 2019). One needs to place the device accurately to measure temperature with more accuracy.

Figure 2: "Ear (tympanic) thermometer"

"Temporal artery (forehead)"

The forehead thermometers are not as reliable as the digital ones and are more expansive than any other thermometer. The heat that comes from a patient’s forehead is measured with infrared sensors to deliver the temperature (Wijaya et al. 2020).

Figure 3: "Celsius vs Fahrenheit" temperature

Temperature Ranges for Humans

The normal body temperature range for every human being is "96.8 degrees Fahrenheit". Moreover, the range is influenced by some factors like age, weight, height, gender, and the level of activity (My.clevelandclinic, 2022). The following table illustrates a better notion of temperature ranges in the human body.

Normal"97 degrees F""99 degrees F"
"Low-graded Fever""98.6 degrees F""100.3 degrees F"
Fever"100.4 degrees F""103 degrees F"
"High-graded Fever""103.1 degrees F"N/A

Table 1: Human body "Temperature ranges"


The usefulness of the thermometer in reading the body temperature is that it can make the marks with the increasing amount of mercury with the interaction of heat. The heat energy converts the amount of content placed in a thermometer to measure the temperature in the body. Anyone can purchase a digital thermometer from any "supermarket pharmacy" or medical store. A thermometer that is using gas as the material inside it, is can also deliver the same reading.


Q1. Which thermometers have not available in the USA?

Ans: Due to the safety purpose, the traditional mercury thermometers are not available to purchase in the US. This type of thermometer can deliver dangers if broken and released the contained mercury, as it is a toxic material for humans if they get contacted.

Q2. What are the drawbacks of "Digital thermometers"?

Ans: Cells in the digital thermometers need to be replaced periodically. Due to the lack of cells, it becomes not useable in any type of emerging situation. With digital, temperature reading can be uncomfortable for oral reading.

Q3. What is the usefulness of thermometers?

Ans: The usefulness of a thermometer can take in the utilisation while measuring the temperature by placing it under the tongue or arms to get an accurate reading of body heat during illness.

Updated on 13-Oct-2022 11:19:47