1.2 Thermometers and Temperature Scales
3 min read•june 24, 2024
are essential tools for measuring , using various physical properties of materials that change with heat. From liquid expansion to electrical resistance, these devices help us quantify temperature across different scales and applications.
Temperature scales like , , and allow us to convert between units and understand extreme temperatures. The concept of and its effects on matter highlight the importance of temperature in physics and everyday life.
Thermometers and Temperature Scales
Properties for temperature measurement
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- Thermometers measure temperature by utilizing the change in physical properties of materials as they are heated or cooled
- Liquid-in-glass thermometers rely on the expansion and contraction of a liquid (mercury or alcohol) in response to temperature changes
- As temperature increases, the liquid expands and rises in the glass tube calibrated to indicate the corresponding temperature
- Bimetallic strip thermometers consist of two different metals bonded together, each with a different of
- As temperature changes, the metals expand or contract at different rates, causing the strip to bend calibrated to indicate the temperature
- Resistance temperature detectors (RTDs) measure temperature by the change in electrical resistance of a metal (platinum) with temperature
- As temperature increases, the metal's resistance increases in a predictable manner measured and converted to a temperature reading
- Thermocouples consist of two dissimilar metals joined together at one end, forming a junction
- When the junction is heated or cooled, a voltage is generated due to the measured and correlated to a specific temperature
- Pyrometers measure temperature of very hot objects by detecting their thermal radiation, allowing non-contact temperature measurement
- Liquid-in-glass thermometers rely on the expansion and contraction of a liquid (mercury or alcohol) in response to temperature changes
Temperature scale conversions
- Celsius to Fahrenheit:
- Fahrenheit to Celsius:
- Celsius to Kelvin:
- Kelvin to Celsius:
- Fahrenheit to Kelvin:
- Kelvin to Fahrenheit:
Absolute zero and Kelvin scale
- is the lowest possible temperature, at which the motion of particles in matter is minimal
- Corresponds to 0 K, -273.15 ℃, and -459.67 ℉
- The is an , with its zero point defined as absolute zero
- Unlike Celsius and Fahrenheit scales, the Kelvin scale does not use negative numbers and is the SI unit for temperature
- At temperatures approaching absolute zero, matter exhibits unique properties
- : Some materials (lead, aluminum) lose all electrical resistance
- : Some fluids (liquid helium) flow without friction
- Bose-Einstein condensates: Matter behaves as a single quantum entity
Fundamental concepts of temperature measurement
- occurs when two objects in contact with each other reach the same temperature, with no net heat transfer between them
- The states that if two systems are in with a third system, they are in thermal equilibrium with each other
- Temperature scales have evolved over time, with developing the in the early 18th century, which is still widely used in some countries today
Key Terms to Review (38)
Absolute temperature scale: An absolute temperature scale is a thermodynamic temperature scale that uses absolute zero as its null point. The two most common absolute temperature scales are Kelvin and Rankine.
Absolute zero: Absolute zero is the lowest possible temperature where all molecular motion ceases. It is 0 Kelvin, or -273.15 degrees Celsius.
Absolute Zero: Absolute zero is the lowest possible temperature, at which the motion of atoms and molecules comes to a complete stop. It is the point at which a system reaches its minimum energy state, and is the coldest possible temperature that can be achieved in the physical universe.
Bimetallic Strip Thermometer: A bimetallic strip thermometer is a type of temperature-measuring device that utilizes the differential thermal expansion of two different metals to indicate temperature changes. It is a common and widely used thermometer for various applications.
Bose-Einstein condensate: A Bose-Einstein condensate is a state of matter formed when a group of bosons, which are particles that follow Bose-Einstein statistics, are cooled to temperatures close to absolute zero. At this point, a significant number of bosons occupy the same quantum state, leading to unique properties like superfluidity and coherence, which are essential for understanding the behavior of particles in different temperature ranges.
Celsius: Celsius is a temperature scale that measures the degree of hotness or coldness of an object or environment. It is based on the freezing and boiling points of water, with 0°C representing the freezing point and 100°C representing the boiling point of water at standard atmospheric pressure.
Celsius Scale: The Celsius scale is a temperature scale that measures temperature based on the freezing and boiling points of water. It is widely used in scientific and everyday applications to quantify temperature in degrees Celsius (°C).
Charles's Law: Charles's law is a fundamental principle in thermodynamics that describes the relationship between the volume and absolute temperature of a gas, given that the pressure and amount of gas remain constant. It states that the volume of a gas is directly proportional to its absolute temperature, provided that the pressure and the amount of gas remain unchanged.
Daniel Gabriel Fahrenheit: Daniel Gabriel Fahrenheit was an 18th-century German physicist who is best known for inventing the Fahrenheit temperature scale, a widely used temperature measurement system. His work on thermometers and temperature scales made significant contributions to the fields of thermometry and meteorology.
Degree Celsius: The degree Celsius (°C) is a unit of temperature on the Celsius scale, where 0°C is the freezing point of water and 100°C is its boiling point at standard atmospheric pressure. It is used widely in most scientific contexts for measuring temperature.
Degree Fahrenheit: Degree Fahrenheit is a unit of temperature measurement in the imperial system, primarily used in the United States. It is based on a scale where the freezing point of water is 32 degrees and the boiling point is 212 degrees under standard atmospheric conditions.
Fahrenheit: Fahrenheit is a temperature scale that measures temperature in degrees Fahrenheit (°F). It is commonly used in the United States and a few other countries, and is based on the freezing and boiling points of water under standard atmospheric pressure.
Fahrenheit Scale: The Fahrenheit scale is a temperature scale that uses degrees Fahrenheit (°F) as the unit of measurement. It is one of the most widely used temperature scales, particularly in the United States, and is based on the freezing and boiling points of water under standard atmospheric pressure.
Isothermal expansion: Isothermal expansion is a thermodynamic process in which a gas expands at a constant temperature. During this process, the internal energy of the gas remains unchanged while work is done by the gas.
Kelvin: Kelvin is the base unit of temperature in the International System of Units (SI), named after the physicist William Thomson, Lord Kelvin. It is a fundamental unit that is used to measure the absolute temperature of a system, providing a scale that is independent of the properties of any particular substance.
Kelvin scale: The Kelvin scale is an absolute temperature scale starting at absolute zero, the point where all molecular motion ceases. It is used in scientific measurements and calculations due to its direct relationship with thermal energy.
Liquid-in-glass thermometer: A liquid-in-glass thermometer is a temperature measuring device that consists of a glass tube containing a liquid, typically mercury or colored alcohol, which expands or contracts in response to temperature changes. This expansion allows the liquid to rise or fall within the glass tube, providing a visual indication of the temperature on a calibrated scale marked on the glass.
Lord Kelvin: Lord Kelvin, also known as William Thomson, was a renowned British physicist and mathematician who made significant contributions to the field of thermodynamics. He is particularly known for his work on the concept of absolute temperature and the development of the Kelvin temperature scale.
Mercury thermometer: A mercury thermometer is a temperature measuring device that uses mercury, a liquid metal, which expands and contracts in response to temperature changes. As the temperature rises, the mercury expands and moves up a calibrated glass tube, indicating the temperature on a scale marked on the tube. This principle of thermal expansion is fundamental to how mercury thermometers function and directly relates to various temperature scales used in scientific measurements.
Pyrometer: A pyrometer is a device used to measure high temperatures, typically in the range of hundreds or thousands of degrees Celsius or Fahrenheit. It is a specialized type of thermometer designed for measuring the temperature of hot, solid, or molten objects.
Resistance Temperature Detector: A Resistance Temperature Detector (RTD) is a type of temperature sensor that uses the principle of electrical resistance changes with temperature to measure temperature accurately. RTDs are made from pure materials, such as platinum, and are known for their high accuracy and stability over a wide temperature range, making them suitable for industrial and laboratory applications. Their resistance increases as the temperature rises, which allows for precise temperature readings.
RTD: RTD, or Resistance Temperature Detector, is a type of temperature sensor that measures temperature by detecting changes in the electrical resistance of a material. RTDs are commonly used in various applications, including industrial process control, HVAC systems, and scientific research, to accurately measure and monitor temperature.
Seebeck Effect: The Seebeck effect is a thermoelectric phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances. This voltage difference can be used to generate electricity or measure temperature.
Specific heat capacity: Specific heat capacity is the amount of heat energy required to raise the temperature of one unit mass of a substance by one degree Celsius (or one Kelvin). It plays a crucial role in understanding how different materials respond to heat and is key in processes like heat transfer, calorimetry, and thermodynamics.
Superconductivity: Superconductivity is a quantum mechanical phenomenon where certain materials exhibit zero electrical resistance and expulsion of magnetic fields when cooled below a critical temperature. This state allows for the unimpeded flow of electric current.
Superconductivity: Superconductivity is a remarkable phenomenon in which certain materials, when cooled below a critical temperature, lose all electrical resistance and can conduct electricity with perfect efficiency, without any energy loss. This unique property has significant implications in the fields of thermometry and the development of advanced superconducting devices.
Superfluidity: Superfluidity is a remarkable quantum mechanical phenomenon that occurs in certain liquids, particularly liquid helium, at extremely low temperatures. It is characterized by the ability of the liquid to flow without any viscosity or resistance, defying the normal laws of fluid dynamics.
Temperature: Temperature is a measure of the average kinetic energy of the particles (atoms or molecules) in a substance. It quantifies the degree of hotness or coldness of an object and is a fundamental concept in thermodynamics that is closely related to the transfer of heat energy.
Temperature Coefficient: The temperature coefficient is a measure of the change in a physical property, such as electrical resistance or the volume of a substance, with respect to a change in temperature. It quantifies the sensitivity of a material or system to temperature variations.
Temperature Conversion: Temperature conversion is the process of transforming a temperature value from one temperature scale to another, such as from Celsius to Fahrenheit or Kelvin. It allows for the comparison and standardization of temperature measurements across different systems.
Thermal equilibrium: Thermal equilibrium is the state in which two or more objects in thermal contact no longer exchange heat, resulting in a uniform temperature throughout the system. This occurs when the temperatures of the objects are equal.
Thermal Equilibrium: Thermal equilibrium is a state in which two or more objects or systems have reached the same temperature and no longer exchange heat energy. This concept is fundamental to understanding temperature, thermometers, heat transfer, and the behavior of thermodynamic systems.
Thermal Expansion: Thermal expansion is the phenomenon where the size or volume of an object increases as its temperature rises. This occurs because the atoms or molecules within the object vibrate more and occupy a larger space as they gain kinetic energy from the increased temperature.
Thermocouple: A thermocouple is a temperature-measuring device that consists of two dissimilar metal wires joined at one end. The temperature difference between the joined end and the other end of the wires produces a small voltage that can be measured and used to determine the temperature at the joined end.
Thermometers: Thermometers are devices used to measure temperature by utilizing the physical properties of materials that change with temperature. They are crucial for accurate thermal measurements in various scientific applications.
Triple Point: The triple point is the temperature and pressure at which the three phases of a substance (solid, liquid, and gas) can coexist in equilibrium. It is a unique point on a substance's phase diagram where the solid, liquid, and vapor phases meet.
Zeroth law of thermodynamics: The zeroth law of thermodynamics states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This law forms the basis for the concept of temperature.
Zeroth Law of Thermodynamics: The zeroth law of thermodynamics states that if two systems are in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other. This law establishes the concept of temperature and provides the basis for temperature measurement.