#boltzmann constant

[doesithavetobeaspider]

Excalibur #55 by Alan Davis

[materialsscienceandengineering]

'Noise thermometry' yields accurate new measurements of Boltzmann constant

New results will contribute to international effort to redefine measurement unit for temperature

By measuring the random jiggling motion of electrons in a resistor, researchers at the National Institute of Standards and Technology (NIST) have contributed to accurate new measurements of the Boltzmann constant, a fundamental scientific value that relates the energy of a system to its temperature. NIST made one measurement in its Boulder, Colorado, laboratory and collaborated on another in China.

These results will contribute to a worldwide effort to redefine the kelvin, the international unit of temperature, and could lead to better thermometers for industry.

Accurate temperature measurement is critical to any manufacturing process that requires specific temperatures, such as steel production. It's also important for nuclear power reactors, which require precise thermometers that are not destroyed by radiation and do not need to be regularly replaced by human workers.

"We live with temperature every day," said Samuel Benz, group leader of the NIST research team involved with the new results. "The current measurements that define the kelvin are 100 times less accurate than measurements defining the units for mass and electricity." The kilogram is known to parts per billion, while the kelvin is only known to a part in a million.

Read more.

[teachersource]

Ludwig Boltzmann was born on February 20, 1844. An Austrian physicist and philosopher, his greatest achievements were the development of statistical mechanics, and the statistical explanation of the second law of thermodynamics. In 1877 he provided the current definition of entropy. Max Planck named the constant kB the Boltzmann constant. Boltzmann's most important scientific contributions were in kinetic theory, including for motivating the Maxwell–Boltzmann distribution as a description of molecular speeds in a gas. Maxwell–Boltzmann statistics and the Boltzmann distribution remain central in the foundations of classical statistical mechanics.

[thescienceage]

Standardizing temperature measures

All of our units of measurement - a foot, a kilogram, an hour, etc. - were developed centuries ago out of necessity and have since been refined with advancing scientific techniques. Today’s technological capabilities are vastly more precise than most people need, but crucial for researchers and engineers. For example, it doesn’t make much sense to define an hour or second as a division of a day anymore. Our instruments are capable of much finer measures than the inconsistencies in a minute from one day to the next. So, we’ve turned to a more reliable, standard definition of a second that relies on physical properties of matter rather than variable large scale properties like the length of a day. The current, technical definition of a second is “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.” Cesium 133 radiation has nothing inherently to do with time, but it’s behavior is exceptionally regular, so we use it as an accurate clock.

...

The other fundamental scientific units - distance, mass, luminous intensity, electric current, amount, and temperature - have been similarly redefined using more precise measures. These fundamental units are the types of unique measurements that can then be used to denote any other measurement, such as how distance (a fundamental unit) and time (a fundamental unit) can be used to express speed (a derived unit). As of today, however, temperature is still missing a definition that relates it directly to its physical source. Temperature’s current definition uses a property of water (its triple point - the temperature and pressure at which all three phases of gas, liquid, and solid exist simultaneously, which is hard to imagine from everyday life, but does happen) to anchor one fixed point of the temperature scale, the other being absolute zero, where atoms do not move at all. However, as researchers have been expanding work in very hot (like stars) and very cold (near absolute zero) temperatures, they’re noticing that this scale doesn’t quite work. While the triple point of water is a physical property, and scientists have carefully controlled the atomic properties of the water used to create the measurement, it’s simply not reliable enough to provide a really precise definition. It’s like trying to time an Olympic sprint with a seconds being 1/86400 of the time from one sunrise to the next.

To fix this problem, researchers at the National Physics Laboratory in Britain are developing a new definition of the temperature scale. They’re using a small amount of pure argon gas to more closely measure the relationship between the energy of atoms and temperature. It’s still a work in progress, but they’ve already broken new ground on the precision of the temperature definition. Their new measurement has almost halved the uncertainty or inaccuracy in the previous standard. For a little perspective, the temperature scale most people use in their daily lives is accurate to about 1 to 5 degrees; this one goes to 0.0000007 degrees.

[Image is the instrument used to contain & measure the argon gas, from the National Physics Laboratory's website.]

[christinetheastrophysicist]

Scientists at the National Physical Laboratory (NPL) have performed the most accurate measurement yet of the Boltzmann constant, which states how much energy at the individual particle level corresponds to each degree of temperature. This measurement could revolutionise the way we define temperature, replacing the standard method that has been used for over 50 years.

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