Questions tagged [metrology]
For questions about the science of measurement, such as how units are defined or how practical measurements are connected to those definitions.
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Can all physical quantities and units be derived from the seven base SI units? [closed]
I understood that from cesium that we derived the unit for second and procedurally with other universal constants we derived the other SI units. Can all other “physical” units be derived from the ...
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Why did we choose Coulomb's constant $k$ as $9\cdot10^9 \rm Nm^2/C^2$ while define unit of charge instead of any other number?
I understand that while defining charge, Coulomb had to choose any arbitrary value of $k$ to describe unit of charge. But, why did we chose $9\cdot10^9 \rm Nm^2/C^2$ as the value of $k$, but not any ...
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Mass of the Prototype $\rm kg$
With the new SI kg based upon Planck's constant $h$, is there any plan to eventually measure the former IPK using a Watt Balance, and determine how far its mass deviates from the new definition of 1 ...
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What is the key difference between SI and MKS units?
In MKS as well SI system, the length, mass and time are measured in the units meter, kilogram and second, respectively. Then how the SI units are different from MKS units? What are the key ...
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What is the value of the ideal gas constant in J/(mol*°C)? [duplicate]
I've seen in some sites that it is the same as in J/(mol*K), is that true?
$8.314 \frac{J}{mol×K}=8.314 \frac{J}{mol×°C}$
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Fundamental and derived physical quantities
I read that fundamental physical quantities are independent of each other but, if we write length = velocity x time, then length depends on the time interval so how come it is independent?
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Are there any non-SI base units? [closed]
Are there any base units that are not in the SI system? If so why aren't they?
Edit: By this I don’t mean other systems that you can convert to (ie. Feet, Ounces, Hours, etc) I mean new base units ...
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How long is a second on the moon?
The Office of Science and Technology Policy, part of the government of the United States of America, issued this statement outlining the need for a Lunar Standard Time (LST) standard. They state:
For ...
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Clarification regarding the meaning of Universal Time UT1
I've been reading the book "From Sundials to Atomic Clocks: Understanding Time and Frequency" by James Jespersen and Jane Fitz-Randolph which is available at https://www.nist.gov/system/...
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Has there been a big change in 1983 when the definition of the metre changed?
The metre was defined at the end of the $18^{th}$ century as the ten-millionth part of the quarter of the meridian (from the north pole to equator). Then, from $1983$ the definition changed for the ...
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Spin-squeezing scaling with the number of particles in one-axis twisting hamiltonian
I am exploring the one axis twisting (OAT) hamiltonian $\hat{H}=\chi S_z^2$ with $S_z=\sum_{i=1}^N\frac{\sigma_z^i}{2}$ and considering the initial state to be $\left|\psi(0) \right>=\left|+x\right&...
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Abbreviations for energy and torque
What are correct abbreviations for torque and energy in US Customary and S.I. systems?
Both include distance and force. Do we write N-m and lbf-ft for both torque and energy? I always heard (years ago)...
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Techniques to measure/picture very low (cryo) temperatures [closed]
I am looking for an experimental technique to measure/create a temperature map of a small object (few mm diameter), like in terms of IR camera.
However, all IR-cameras I encountered measured ...
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Fisher information of parametric channel
Suppose $\Phi_\theta$ is a quantum channel whose action can be written for any state $\rho\in \mathcal S(\mathcal H_S)$ in the Stinespring representation as $\Phi_\theta(\rho)= \text{Tr}_E(U_\theta (\...
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What was defined first and how? The ampere or the vacuum permeability?
I've been looking up the history and evolution of the seven base units and am currently checking out the ampere. What I've found is that 1A is defined as the current in a wire which would experience a ...
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