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.
391 questions
-6 votes
0 answers
99 views
Is the measured value of G a true constant, or an average affected by internal structure and attenuation? [closed]
The gravitational constant G has been measured in various experiments since Cavendish, but nearly all assume that macroscopic bodies (like test masses or the Earth) act as uniform sources of gravity. ...
1 vote
1 answer
100 views
Are the topics in philosophy of measurement used in practice by professional experimental physicists or metrologists? [closed]
I recently stumbled across the three-volume "Foundations of Measurement" (by David H. Krantz, R. Duncan Luce, Patrick Suppes, and Amos Tversky) and the Stanford Encyclopedia of Philosophy ...
2 votes
1 answer
143 views
How we assigned a charge to everything after defining the charge of electron?
One ampere corresponds to the flow of approximately $6.241 509 074 × 10^{18}$ elementary charges passing a cross-sectional area in one second as per the 2019 revision of SI, fixing the elementary ...
- 432
3 votes
3 answers
733 views
To what extent can we trust a measurement and its uncertainty?/Is there a rigorous framework for measurement?
The underlying driving question here is really just "How do I trust a measurement?" Ultimately, I'd like an answer(s) that applies to any measuring device (be it a voltmeter, telescope data, ...
6 votes
4 answers
1k views
Very elementary question - would this work as a primitve definition of mass?
I have recently been thinking a lot about foundational quantities in physics and chemistry (I study chemistry as an undergraduate), and how to define them. It seems quite easy to define at least time ...
- 1,253
2 votes
1 answer
130 views
Mathematical model of the escapement mechanism, proving it can keep time accurately?
There are a few types of escapement mechanism, a pendulum escapement (used in grandfather clocks) and torsional pendulum escapement (verge & palette). Has anyone devised a mathematical model of ...
0 votes
1 answer
147 views
Why are there no universal constants associated with candela?
I'll start by saying that I'm more oriented towards the math community and I hope to write a good question. Context I'm taking a quantum mechanics course where the professor is using a convention ...
- 101
3 votes
3 answers
386 views
What are the units of mass flux?
I see 'mass flux' and 'mass flow rate' both used for the same system (ex: Mass flux across a volume). From various sources it seems like 'mass flux' should have SI units $\mathrm{kg \times s^{-1}\...
- 412
4 votes
2 answers
234 views
Why is the permeability of free space $\mu_0$ equal to $4\pi*10^{-7}\mathrm{\frac{N}{A^2}}$?
I understand why we might expect to see a $4\pi$ in $\mu_0$, given that we see relationships between geometry and natural phenomena, like with Gauss's law giving us $k_e = \frac{1}{4\pi\varepsilon_0}$ ...
- 41
0 votes
0 answers
91 views
Why is there a slight mismatch between the definition of the lumen and the peak of the luminosity function?
The lumen (symbol: lm) is the unit of luminous flux in the SI. The lumen is defined by taking the fixed numerical value of the maximum photopic luminous efficacy to be exactly $683$ lm/W.....or so I ...
- 1,653
1 vote
1 answer
168 views
Quantum estimation of a parameter affected by the measurement
Usual textbook quantum mechanics tells us that observable quantities are associated with Hermitian operators. However, there are many instances where we seek to measure parameters encoded in the ...
- 193
0 votes
0 answers
84 views
Quantum Metrology: rotation of a small object
Let's assume I have a rotating object (think of it as a small sphere) and that I want to learn (estimate) its angular velocity, call it $\Omega$. I want to frame the problem from a quantum parameter ...
- 193
8 votes
2 answers
214 views
Since the 2019 SI definition change, are the conversions between dynes and Newtons, and ergs and Joules exact?
In 2019 the SI system changed so that, although the product $\mu_0 \epsilon_0$ is a defined quantity, their individual values are no longer fixed. In SI formulae, the force between two charges or ...
- 144k
11 votes
4 answers
2k views
Why is the permeability of the vacuum exact, and why must the permittivity be determined experimentally?
In G. R. Fowles' Introduction to Modern Optics, the author writes: The constant $\mu_0$ is known as the permeability of the vacuum. It has, by definition, the exact value: $$4\pi\times 10^{-7} \ \ \...
0 votes
1 answer
218 views
CGS unit of heat calorie or erg?
Heat is one kind of energy. As the cgs unit of energy is erg, so the cgs unit of heat also be erg. But in book, it show that the cgs unit of heat is calorie. please explain..
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