What is Thermometer? Definition, Types & Examples

Thermometer 

A thermometer is a useful and important tool that measures temperature. It shows how hot or cold something is by giving a clear number. Thermometers are used in homes, hospitals, laboratories, kitchens, industries and outdoor environments. Early thermometers were simple devices that used liquid inside a thin glass tube. 

Today, many modern types of thermometers exist, such as digital thermometers and infrared thermometers. Students should learn more about thermometers, including their different types and examples. This topic also explains how a thermometer works, the main types of thermometers, thermometers used for liquids, what is inside a thermometer, its uses, and other useful facts.

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What Is a Thermometer?

A thermometer is an instrument used to measure temperature. In simple terms, it shows how hot or cold something is. The word comes from the Greek words thermos (heat) and metron (measure). So, a thermometer is a “heat-measuring device.”

Early devices for measuring temperature appeared in the 17th century, including Galileo’s thermoscope. It showed heat changes but did not give numbers. Later inventions led to more accurate liquid-in-glass thermometers.

Modern thermometers are designed to be fast, safe, and easy to read. Many now use electronic sensors instead of liquids, and some can measure temperature from a distance. 

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Types of Thermometer

There are many types of thermometer, and each one is designed for a specific task. Below are the main types of thermometer:

1. Clinical Thermometer

A clinical thermometer is used to measure body temperature. Its scale usually ranges from 35°C to 42°C. Earlier versions used mercury, but now digital versions are more common because they are safer and quicker.

2. Laboratory Thermometer

A laboratory thermometer is used in scientific work to measure liquid temperature. It is a thermometer for liquids and has a wide measurement range, such as –10°C to 110°C. It helps measure chemicals, water, and other substances during experiments.

3. Digital Thermometer

A digital thermometer uses electronic sensors to detect temperature. The reading appears on a small screen. It is widely used because it gives quick and accurate results and does not use mercury.

4. Infrared Thermometer

Infrared thermometers measure temperature without direct contact. They detect infrared radiation emitted by objects. These thermometers can measure skin temperature, machine parts, food surfaces, and other objects safely from a distance.

5. Mercury Thermometer

A mercury thermometer contains mercury, a liquid metal that expands when heated. As temperature increases, the mercury rises inside a narrow tube. These thermometers are accurate but less common now because mercury is toxic if the device breaks.

6. Alcohol Thermometer

This thermometer uses colored alcohol instead of mercury. Alcohol thermometers are safer and can measure very low temperatures because alcohol does not freeze easily. Many also have bright colors that make readings easier.

7. Gas Thermometer

A gas thermometer measures temperature through changes in gas pressure. It is very accurate and mainly used for scientific research.

8. Thermocouple Thermometer

A thermocouple uses two different metals joined together. When heated, the metal junction produces a small voltage. The thermometer reads this voltage and converts it into temperature. Thermocouples are used in industries, ovens, furnaces, and factories.

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How Does a Thermometer Work?

Each thermometer works on a scientific principle, such as expansion of liquids or changes in electrical properties.

1. Liquid-in-Glass Thermometers

This includes mercury and alcohol thermometers. They work on thermal expansion, which means a material expands when heated. Here is how they work:

• The thermometer contains a liquid in a thin glass tube.

• When temperature increases, the liquid expands and rises in the tube.

• The scale printed on the glass shows the temperature.

This is why a thermometer for liquids is commonly used for simple temperature readings.

2. Digital Thermometers

Digital thermometers use electronic sensors, usually thermistors or other temperature-sensing elements. How they work:

• Sensors detect changes in electrical resistance when temperature changes.

• A microchip converts those changes into a temperature reading.

• The reading appears on the digital display.

These thermometers are safe, fast, and very accurate.

3. Infrared Thermometers

Infrared thermometers work without touching the object. 

• All objects give off infrared radiation.

• The thermometer’s sensor detects this radiation.

• A processor calculates the temperature based on the radiation level.

• The display shows the final reading.

Infrared thermometers are helpful when measuring moving, hot, or distant objects.

4. Gas Thermometers

A gas thermometer measures temperature by observing changes in the pressure of a gas.

• When heated, gas particles move faster and increase pressure.

• This pressure change is measured and used to calculate temperature.

5. Thermocouples

Thermocouples work through electrical voltage changes.

• Two different metals create a junction.

• When heated, the junction produces a voltage.

• The amount of voltage depends on temperature.

• The device converts this into a temperature reading.

Read More: Difference Between Physical and Chemical Changes

What’s Inside a Thermometer?

Understanding what’s inside a thermometer makes it easier to see how it functions. Different thermometers contain different parts.

1. Mercury Thermometer

Inside these thermometers, there is:

• A narrow glass tube

• Mercury liquid

• A small bulb at the bottom

• A temperature scale along the tube

The mercury moves upward when heated.

2. Alcohol Thermometer

Inside these thermometers, there is:

• Colored alcohol

• A thin glass tube

• A measuring scale

Alcohol expands in the tube when the temperature increases.

3. Digital Thermometer

A digital thermometer contains:

• Temperature sensors

• A microprocessor

• A battery

• A digital screen

• Wiring and small circuits

These parts work together to convert electrical changes into readable numbers.

4. Infrared Thermometer

These thermometers include:

• Infrared sensors

• Lenses for focusing radiation

• A microcontroller

• A display screen

• Internal circuits

These parts allow the device to read temperature without direct contact.

5. Thermocouple Thermometer

Inside a thermocouple, there are:

• Two different metal wires

• A junction where the wires are joined

• A voltmeter or a digital circuit

• A display unit

These parts detect voltage changes that correspond to temperature.

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Uses of Thermometer

Temperature plays a key role in daily life, health, food safety, and scientific work. Below are the major uses.

1. Medical Uses

Thermometers help:

• Check fever

• Measure body temperature during illness

• Monitor temperature during medical procedures

Digital and clinical thermometers are common in healthcare.

2. Scientific Uses

In scientific work, thermometers measure:

• Temperature of liquids

• Chemical reactions

• Solutions and mixtures

• Air and gas temperature

Laboratory thermometers and thermometers for liquids are common for experiments.

3. Industrial Uses

Industries use thermometers to:

• Check machine and engine temperatures

• Monitor furnaces and boilers

• Measure refrigeration temperatures

• Maintain product safety

Thermocouples and infrared thermometers are often used.

4. Cooking and Food Safety

Thermometers help ensure food is cooked correctly and safely. They are used to:

• Measure oven temperature

• Check internal temperature of meat

• Avoid undercooking or overcooking

• Maintain hygiene and food safety standards

Kitchen thermometers help prevent foodborne illness.

5. Environmental and Weather Uses

Thermometers also help measure:

• Air temperature

• Soil temperature

• Water temperature in lakes, oceans, and rivers

• Weather conditions

These readings help understand climate and natural environments.

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Facts About Thermometer

The following are some interesting thermometers facts:

• Galileo created an early temperature-measuring device called a thermoscope in the 1600s.

• The Celsius and Fahrenheit temperature scales were named after the scientists who created them.

• Mercury thermometers are less common today because mercury is dangerous if the thermometer breaks.

• Digital thermometers provide fast and safe readings without mercury.

• Infrared thermometers are useful for measuring temperature from a distance.

• A thermometer for liquids remains essential in laboratories because it provides consistent readings.

• Thermocouples can measure very high temperatures, even above 1000°C.

• Some modern thermometers can connect to smartphones to store and track temperature data.

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