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---------------- - 1959 - Weights and measures and Metric Standards
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- We need to measure the kilogram standards to a few parts per billion. These standards all started in Paris in 1889 the year the Eiffel Tower opened. The mass of a platinum-iridium cylinder, half the size of a can of tuna, yet with $40,000 invested to keep it under 3 nested glass bell jars, is the world’s standard.
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- In 2018 we hope to have a new standard not tied to a physical object, but, tied directly to Planck’s Constant. Tied to a photon, the amount of energy carried by a single particle of light.
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- In 1983 the meter was defined as the distance between two etched lines on a platinum-iridium bar. Today we use the standard as the distance light travels in 1 / 299,792,458th of a second. In 1791 this distance was defined as one the-millionth of one forth of the Earth’s circumference, the meridian.
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- In 1967 the second was defined as 9,192,631,770 wavelengths of a cesium -133 atom. Originally the second was 1 / 86,400th of a mean solar day.
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- Planck’s constant is the relation of “ quantized” light and matter. It is a sub-atomic scale constant. For example: Green light has a wavelength of 555 nanometers with a frequency of 540*10^12 hertz ( wavelengths per second). Each photon (quantum of light) = h * f = 3.58 * 10^-19 Joules.
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--------------------- h = Planck’s Constant
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-------------------- E = h * f
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-------------------- Energy = Planck’s Constant * frequency
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--------------------- E = h * c / w
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--------------------- c = speed of light
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---------------------- w = wavelength of light.
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- Planck’s Constant = 6.625 *10^-34 kilogram * (meters)^2 per second
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- “h” also equals 4.136*10^-15 electron volts * seconds / 2*pi cycles.
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- The “Kibble-Balance” is designed to measure a mass of 1 kilogram. It tests the downward gravitational force to exactly match the magnetic field from running current through a coil. Current and voltage and electric resistance are then used to determine Planck’s Constant. The Kibble-Balance can measure mass to 100 parts per billion error. The Kibble- Balance can also be used to precisely measure electric current, the ampere. The magnetic force between two coils of wire is measured by the amount of weight of the other arm of the balance to achieve equilibrium.
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- The idea is to eventually get the kilogram defined in terms of Planck’s Constant within an uncertainty of less than 20 parts per billion.
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- The candela is a measure of luminosity. In 1979 it was defined as monochromatic radiation of frequency 540*10^12 hertz having radiant intensity of 1/ 683 watts per steradin ( a solid angle). The earliest definition was simply the luminosity of a carbon-filament lamp. A computer liquid crystal display is 250 candela / meters^2. A high definition TV ranges from 450 to 1500 candela / m^2
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- The ampere is one Coulomb per second , or, 6.242*10^18 electrons per second. The ampere is a unit of current, the coulomb is a unit of charge. A 12 volt headlight is 5 amperes. The starter motor is 80 to 160 amperes. A 60 watt light bulb is 500 milliamperes.
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- In 1946 two straight parallel conductors of infinite length one meter apart in a vacuum have a force of 2*10^-7 Newtons per meter of length. A new definition to be developed would use the charge carried by a single proton.
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- The Kelvin is a measure of temperature. In 1967 the Kelvin was set at 1 / 273.16 of the thermodynamic temperature of triple point of water. Triple Point is the temperature and pressure where water exists as a liquid, a gas, and a solid ice, all at once.
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- A mole is a small furry animal that burrows under ground. He has inconspicuous eyes and ears and is adept at underground breathing with little oxygen. His main diet is earthworms. A mole is also a unit of measure, the amount of a substance, It is the number of atoms of a substance compared to 12 grams of carbon-12. Expressed as Avogadro’s Constant there are 6.022*10^23 particles per mole.
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- These standards above are the seven base units that are the Standards for the Metric System.
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---------------------- meter, second, candela, kilogram, ampere, Kelvin, mole.
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- Another 22 standards are built from these seven. Achieving and maintaining these standards is among the 5 toughest undertakings in physics. Right up there with detecting the Higgs Boson and detecting gravitational waves.
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- To make a measurement is must be versus something, that something is a standard that everyone can agree on. It has progressed technology through the ages. Stay tuned , there is still more to learn.
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- Note (1): Request any of the Reviews by number to learn more.
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- Review #1116 for standard candles for particular stars.
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- Complete index of all reviews is available upon request.
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