What Does a Thermometer Measure?


A thermometer is a device used to measure temperature. It is an essential tool in various fields, including weather forecasting, healthcare, and scientific research. Understanding what a thermometer measures and how it works is crucial for accurate temperature readings and reliable data analysis. In this article, we will delve into the details of what a thermometer measures and explore the different types of thermometers available.

The Concept of Temperature

To comprehend what a thermometer measures, we must first understand the concept of temperature. Temperature refers to the degree of hotness or coldness of an object or environment. It is a measure of the average kinetic energy of the particles within a substance. The higher the temperature, the greater the kinetic energy and vice versa.

The Role of Thermometers

Thermometers play a crucial role in measuring temperature accurately. They provide a quantitative value that allows us to compare the hotness or coldness of different objects or environments. By measuring temperature, thermometers enable us to monitor and control temperature-dependent processes, evaluate health conditions, and make informed decisions based on temperature data.

Types of Thermometers

There are several types of thermometers available, each utilizing different principles to measure temperature. Let’s explore some of the most common types:

1. Mercury Thermometers

Mercury thermometers have been widely used in the past but are now being phased out due to the potential health and environmental risks associated with mercury. They operate on the principle that mercury expands or contracts with changes in temperature. The length of the mercury column within the thermometer indicates the temperature.

2. Digital Thermometers

Digital thermometers are among the most commonly used thermometers today. They use electronic sensors to measure temperature and display the results digitally. Digital thermometers offer quick and accurate readings, making them suitable for both personal and professional use.

3. Infrared Thermometers

Infrared thermometers, also known as non-contact thermometers, measure temperature without making physical contact with the object or person being measured. They detect infrared radiation emitted by the object and convert it into temperature readings. Infrared thermometers are commonly used in industrial settings, medical facilities, and food service industries.

4. Thermocouple Thermometers

Thermocouple thermometers use the principle of thermoelectric effect to measure temperature. They consist of two dissimilar metal wires joined together at one end. When there is a temperature difference between the junction and the free ends of the wires, a voltage is generated, which can be measured and correlated to the temperature.

5. Resistance Thermometers (RTD)

Resistance thermometers, also known as resistance temperature detectors (RTD), rely on the change in electrical resistance of metals with temperature. Platinum is commonly used as the sensing element in RTDs due to its stable and predictable resistance-temperature relationship. RTDs provide accurate and stable temperature measurements, making them suitable for various scientific and industrial applications.

6. Bimetallic Strip Thermometers

Bimetallic strip thermometers consist of two different metals bonded together to form a strip. As temperature changes, the metals expand or contract at different rates, causing the strip to bend. The bending of the strip is proportional to the temperature change, allowing for temperature measurement.

7. Liquid Crystal Thermometers

Liquid crystal thermometers utilize the unique properties of liquid crystals to indicate temperature. Liquid crystals change their color or opacity based on temperature variations. These thermometers contain a strip or patch of liquid crystals that display different colors corresponding to different temperatures.

Factors Affecting Thermometer Accuracy

While thermometers are designed to provide accurate temperature measurements, several factors can affect their accuracy. It is essential to consider these factors when using a thermometer:

1. Calibration

Thermometers need to be calibrated regularly to ensure accurate readings. Calibration involves comparing the thermometer’s measurements with a reference standard thermometer and making necessary adjustments if there are discrepancies.

2. Environmental Conditions

The surrounding environment can influence thermometer accuracy. Factors such as air temperature, humidity, and exposure to direct sunlight can affect the readings. It is important to use thermometers in controlled environments whenever possible.

3. Human Errors

Human errors, such as improper placement of the thermometer or misinterpretation of readings, can lead to inaccurate temperature measurements. It is crucial to follow the manufacturer’s instructions and guidelines to minimize human errors.

4. Response Time

Thermometers have different response times, which refers to the time taken to reach a stable temperature reading. Faster response times are essential for applications where quick temperature measurements are required.

FAQs (Frequently Asked Questions)

  1. Q: How does a mercury thermometer work?

    A: A mercury thermometer works by utilizing the expansion and contraction of mercury with changes in temperature. The mercury column within the thermometer rises or falls, indicating the temperature.

  2. Q: Are digital thermometers more accurate than mercury thermometers?

    A: Yes, digital thermometers are generally more accurate than mercury thermometers. They provide precise readings and eliminate the risk of human errors associated with reading the mercury column.

  3. Q: Can infrared thermometers measure body temperature?

    A: Yes, infrared thermometers can measure body temperature by detecting the infrared radiation emitted by the skin. However, they should be used correctly and at an appropriate distance from the body to ensure accurate readings.

  4. Q: Are bimetallic strip thermometers suitable for measuring extreme temperatures?

    A: Bimetallic strip thermometers can be used for measuring a wide range of temperatures, including extreme temperatures. However, their accuracy may be affected at extremely high or low temperatures, and specialized thermometers may be more suitable for such applications.

  5. Q: How often should thermometers be calibrated?

    A: Thermometers should be calibrated at regular intervals, as specified by the manufacturer or relevant industry standards. The frequency of calibration depends on factors such as the thermometer type, intended use, and environmental conditions.

  6. Q: Can resistance thermometers be used in harsh environments?

    A: Resistance thermometers, particularly those with platinum sensing elements, can withstand harsh environments and provide accurate measurements. They are resistant to corrosion and exhibit excellent stability over time.

  7. Q: Do liquid crystal thermometers require batteries?

    A: No, liquid crystal thermometers do not require batteries. They rely on the temperature-induced color changes of liquid crystals and do not involve any electronic components.

  8. Q: Can I use a thermometer designed for industrial applications for measuring body temperature?

    A: Thermometers designed for industrial applications may not be suitable for measuring body temperature accurately. It is recommended to use thermometers specifically designed and validated for measuring body temperature.

  9. Q: Are there any safety concerns with mercury thermometers?

    A: Yes, mercury thermometers pose safety concerns due to the toxic nature of mercury. Accidental breakage can release mercury vapor, which is harmful if inhaled. It is advisable to use alternative thermometers, such as digital or infrared thermometers.

  10. Q: Can thermometers measure temperature in different units?

    A: Yes, many thermometers allow users to select different temperature units, such as Celsius, Fahrenheit, or Kelvin. The selected unit determines the scale displayed on the thermometer.


Thermometers are invaluable tools that enable accurate temperature measurement in various fields. They measure the degree of hotness or coldness, allowing us to monitor, control, and make informed decisions based on temperature data. Understanding the different types of thermometers and their principles of operation is essential for obtaining reliable temperature measurements. By considering factors that can affect thermometer accuracy and following proper calibration procedures, we can ensure accurate and meaningful temperature readings.

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