Are you wondering how Thermometers Measure Temperature? A thermometer measures temperature through a glass tube sealed with mercury, which expands or contracts as the temperature rises or falls. The tiny bulb and micro-fine tube help the mercury rapidly reach the temperature it is measuring.
You wear thermal underwear to stop body heat from escaping. Despite its name, a thermometer doesn’t record heat, but relative temperature.

Thermometers Measure Temperature
Thermometers are devices used to measure temperature. Temperature is a measure of the average kinetic energy of the particles in a substance, which determines how hot or cold an object is. Thermometers work on the principle that materials expand or contract with temperature changes.
When a substance is heated, its particles gain energy and move faster, causing the substance to expand. Conversely, when a substance is cooled, its particles lose energy and move more slowly, causing it to contract.
Thermometers typically use various physical properties of materials that change with temperature to provide a quantitative temperature measurement.
Liquid-in-glass thermometers
These consist of a bulb containing a liquid, typically mercury or alcohol, connected to a glass tube with a calibrated scale. As the temperature changes, the liquid expands or contracts, causing it to move up or down the glass tube, indicating the temperature on the scale.
Bimetallic strip thermometers
These have a strip made of two different metals with different coefficients of thermal expansion bonded together. The metals expand or contract at different rates as the temperature changes, causing the strip to bend. The amount of bending is used to determine the temperature.
Gas thermometers
These use the principle of gas expansion with temperature change. A gas, such as hydrogen or helium, is enclosed in a container with a calibrated scale. As the gas absorbs or loses heat, it expands or contracts, and the resulting change in pressure or volume determines the temperature.
Digital thermometers
These use electronic sensors, such as thermistors or thermocouples, to measure temperature and display the reading digitally. These are commonly used in modern applications due to their accuracy, speed, and ease of use.
Thermometers are used in various fields, including meteorology, medicine, industry, and research, to measure and monitor temperature for multiple applications.
How Do Thermometers Measure Temperature
Thermometers are tools used in various fields, from medicine and weather forecasts to cooking and scientific research. They provide accurate temperature readings, enabling us to make informed decisions and ensure safety and comfort. But have you ever wondered how thermometers measure temperature? Let’s delve into the science behind these fascinating devices.
Thermometers operate based on the concept of thermal expansion – the tendency of matter to expand or contract in response to changes in temperature. A thermometer typically consists of three main components: a temperature sensor, a scale, and a display.
The temperature sensor, also known as a thermometric element, is the core part of a thermometer. It is responsible for detecting and responding to changes in temperature. Different types of sensors are used in various thermometers, each with its advantages and limitations.
The most common type of temperature sensor is a mercury-in-glass thermometer. It consists of a small glass bulb attached to a thin capillary tube filled with mercury. As the temperature rises, the mercury inside the bulb expands, causing it to grow in the capillary tube. The temperature can be determined using a marked scale by measuring the length of the mercury column.
Digital thermometers, on the other hand, use electronic detectors such as resistance temperature detectors (RTDs) or thermocouples. RTDs measure temperature based on the change in electrical resistance of a metal wire as it heats up or cools down. On the other hand, thermocouples generate a small voltage when exposed to a temperature gradient. By measuring this voltage, the temperature can be determined accurately.
Temperature and Heat are Two Radically Different Concepts
A thermometer measures temperature through a glass tube that expands or contracts with mercury as the temperature rises or falls. The bulb’s tiny size and the tube’s micro-fine size help the mercury reach the temperature it is measuring very rapidly.
What are the 3 Ways to Measure Temperature?
Key Concepts
1. There are three different systems for measuring heat energy (temperature): Fahrenheit, Celsius, and Kelvin
2. In scientific measures, it is most common to use either the Kelvin or Celsius scale as a unit of temperature measurement
3. Nothing can be colder than absolute zero, which is the point at which all molecular motion ceases
Does a Thermometer Measure Heat or Temperature?
You wear thermal underwear to prevent body heat from escaping. Despite its name, a thermometer doesn’t record heat but temperature. Temperature and heat are two radically different concepts. Two other scales, the Fahrenheit scale and the Celsius scale, can be found on thermometers.
So, he made a thermometer, stuck it in freezing water, and marked the extent of the mercury on the glass as 32 degrees. Then he stuck an equivalent thermometer in boiling water and marked it 212 degrees. He then put 180 evenly spaced marks between those two points.
Types of Thermometers
Bulb thermometers are most commonly found outside on porches or under tongues, measuring the temperatures outside or our bodily temperatures.
With age, technology brought the invention of other types of thermometers. Each has its distinctive means of measuring or controlling temperature.
For instance, bimetallic strip thermometers are highly effective for controlling temperatures. Although bulb thermometers are suitable for measuring temperature accurately, they make it harder to maintain set temperatures.
While bulb thermometers measure our changing temperatures when we feel feverish, bimetallic strip thermometers help us bake our favorite cakes by maintaining a set temperature in ovens.
Recent technology has created new ways to measure temperatures with electronics. This sensor changes its resistance with temperature changes.
A computer or other electronic circuit measures the resistance and converts it to a temperature to display it or decide whether to turn something on or off.
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Can Thermometers Measure Below 0 Degrees?
A Mercury thermometer is employed to measure temperatures above zero degrees Celsius. Mercury expands upon heating and may be a good thermal conductor. It is also a bright liquid, making it convenient for temperature measurement.
(FAQs)
Q: How do thermometers measure temperature?
A: Thermometers measure temperature by using a temperature-sensitive material that undergoes a physical change in response to changes in temperature. This change is then measured and converted into a temperature reading.
Several types of thermometers exist, including liquid-in-glass thermometers, bimetallic strip thermometers, thermocouples, resistance temperature detectors (RTDs), and infrared thermometers, each with a specific mechanism for measuring temperature.
Q: How does a liquid-in-glass thermometer work?
A: A liquid-in-glass thermometer typically consists of a bulb filled with a temperature-sensitive liquid, such as mercury or alcohol, connected to a glass tube with a calibrated scale.
The liquid expands or contracts when the temperature changes, causing it to rise or fall in the glass tube. The temperature is then read from the scale at the liquid level in the tube, providing the temperature measurement.
Q: How does a bimetallic strip thermometer work?
A: A bimetallic strip thermometer measures temperature using the principle of differential expansion of two different metals. It consists of two strips of different metals bonded together, such as brass and steel, with varying coefficients of thermal expansion.
When the temperature changes, the two metals expand or contract at different rates, causing the bimetallic strip to bend. The amount of bending is proportional to the temperature change, and this bending is measured and converted into a temperature reading.
Q: How do thermocouples work?
A: Thermocouples work based on the principle of the Seebeck effect, which is the generation of a voltage across the junction of two different metals when there is a temperature gradient. A thermocouple consists of two wires of various metals, connected at one end to form a junction.
When the junction is exposed to a temperature gradient, a voltage proportional to the temperature difference is generated. This voltage is measured and converted into a temperature reading.
Q: How do resistance temperature detectors (RTDs) work?
A: Resistance temperature detectors (RTDs) measure the change in electrical resistance of a temperature-sensitive material, usually platinum, with temperature changes.
RTDs typically consist of a coil or wire made of temperature-sensitive material connected to an electrical circuit. As the temperature changes, the material’s resistance changes, and this change in resistance is measured and converted into a temperature reading.
Q: How do infrared thermometers work?
A: Infrared thermometers measure temperature by detecting the thermal radiation emitted by an object. They use a lens to focus the infrared radiation onto a detector, which then converts the radiation into an electrical signal.
The electrical signal is then processed and converted into a temperature reading based on the intensity of the emitted radiation. Infrared thermometers are commonly used for non-contact temperature measurements, such as measuring the temperature of a person’s forehead or the surface of an object.
A Final Note
Attempts at standardized temperature measurement before the 17th century were crude at best. For instance, in 170 AD, physician Claudius Galenus mixed equal portions of ice and boiling water to make a “neutral” temperature standard.
The modern scientific field originates in the works of Florentine scientists in the 1600s, including Galileo, who constructed devices ready to measure the relative temperature change, but also subject to confounding by atmospheric pressure changes.
These early devices were called thermoscopes. Ferdinand II, Prince of Tuscany, constructed the first sealed thermometer in 1654.
Fahrenheit’s scale remains in use, alongside the Celsius and Kelvin scales. Read more how do thermometers measure temperature or other articles on how to clean a thermometer.
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