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Questions tagged [physical-constants]

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3
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0answers
35 views

Planck's constant calculated by photoelectric effect laboratory is off

I conducted an experiment today where I had to use a photocathode of unknown material (model: Daedalon Corporation Photoelectric Effect EP-05) and study the photoelectric (PE) effect to make a ...
-1
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0answers
39 views

Planck units and other constants

Why is it that only $G$, $\hbar$ and $c$ are used as the three fundamental constants. What about the ratio of the mass of a proton to an electron, or the quantity of dark energy, and so on?
3
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1answer
66 views

Regarding the Boltzmann entropy formula, is the Boltzmann constant really arbitrary?

In the top answer to this question (Is the Boltzmann constant really that important?) I read that the Boltzmann constant is just a dummy factor which converts energy to temperature. But that allows ...
0
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1answer
24 views

Which reference should I use for molar masses of chemical elements?

This question is more related to the academical application of Physics than to Physics per se. I'm currently doing my thesis, and it involves a lot of molar masses in the calculations. I would like to ...
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0answers
26 views

What is a global limit in gauged supergravity?

Does anyone know what a global limit (rigid limit), where the gauge coupling constant is zero, in gauged supergravity is?
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2answers
76 views

How did Maxwell figure out the speed of light?

The Wiki article is about 2 graduate years of physics beyond my understanding. What is a good high-school rendition of his thought process: regarding his use of the "distributed capacitance and ...
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2answers
51 views

Are particle decay times universal constants?

Basically what the title says. For neutrinos, for example.
1
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1answer
61 views

What is the dimension of the weak gauge field couplin constant NOT in natural units?

What is the dimension of g and g', NOT in natural units, but in terms of mass, length, time, and permittivity?
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1answer
32 views

What parameters determine the probability of virtual photon emission/absorption?

Suppose an electron is producing an electric field by emission of virtual photons and interacting with other particles. What parameters determine the probability that it will emit at least one virtual ...
0
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1answer
38 views

Precise value of spin in Nms?

What is the exact value of the spin of a particle with a 'spin' of 'one'? In units of Nms (Newton-meter-second)? And does a boson really have a spin of exactly one, or has that been 'normalized'? ...
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3answers
190 views

Redefinition of everything on May 20th, 2019 [closed]

A couple of issues: So after May 20th, 2019, what exactly will be the defined value of $\hbar$? What will be the defined number of elementary charges in a Coulomb? Then $\mu_0$ and $\epsilon_0$ will ...
4
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2answers
115 views

Why is the resolution or measurement uncertainty of $G$ so bad?

I sorta know how the Cavendish apparatus works, and I know that "Gravity is an extremely weak force" for subatomic particles in comparison with the E&M or nuclear forces that act on these ...
0
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0answers
31 views

Schrödinger equation from Dirac–von Neumann axioms

Using Dirac–von Neumann axioms, it isn't too difficult to derive $$\frac{d}{dt}\left|\psi\right>=ikH\left|\psi\right>,$$ where $H$ is some hermitian operator. However, how would one show that $k=...
2
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1answer
49 views

Electrostatic in 2D: dimensional analysis

After reading this very interesting post about the electric field and the electric potential of a point charge in 2D and 1D, I've understood that, for the $2D-$case, the following formulas hold: $$ \...
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2answers
38 views

When was Coulomb's constant made/established?

Charles-Augustin de Coulomb lived from 14 June 1736 – 23 August 1806. Coulomb's constant is $$k_{\text e}=\alpha\frac{\hbar c}{e^2},$$ a form of Planck's constant is included, but Max Planck lived ...
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2answers
43 views

Why is it important to measure permittivity and permeability complex of materials?

I know that in general, $\epsilon(r,\omega)$ and $\mu(r,\omega)$ are complex tensors, so now how do you resolve maxwell equations? I don't understand why there are techniques to measure them if you ...
2
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1answer
70 views

Time-varying gravitational constant a 'well-posed' question?

To my knowledge, some famous physicists such as Dirac and Dyson (perhaps among others) have advocated for the possibility that Newton's gravitational constant $G_N$ might be "time-dependent". I have ...
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1answer
65 views

How did Newton use his theory without the value of $G$? [duplicate]

I know that Newton extensively used his theory of gravity to calculate many things, but how did he do so without actually knowing the value of the gravitational constant $G$? Did he estimate it ...
3
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2answers
90 views

Are $2$ and $1/2$ universal constants? [closed]

For example, if the equation for energy were: $$E = mc^{2.713397972993}$$ clearly $2.713397972993$ would be a universal constant. And in the Einstein field equation: $$R_{\mu \nu} - \tfrac{1}{2}R \...
5
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1answer
150 views

Fine Tuning of the Universe

I'm an A level student looking into the fine tuning of various constants. Physicists explain the extensive effects that would happen if these constants were to be changed/different and hence, how this ...
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0answers
74 views

What is the role of $\hbar$ in quantum mechanics? [duplicate]

Planck's constant $\hbar$ appears in the Schrodinger equation: $$i\hbar \frac{d|\psi\rangle}{dt}\ = \hat{H}|\psi\rangle$$ which implies for stationary states, $$|\psi(x,t)\rangle=e^{-iE_n/\hbar}|\...
3
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1answer
135 views

What's going on with the Hubble constant?

I'm doing a small project on LIGO for a third-year project at University. I want to write something about how LIGO can be used to measure $H_0$, which would be useful because the current state of the ...
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1answer
60 views

Are constants derived or calculated?

I am currently writing up a lab report on the determination of Planck's constant using x-ray diffraction and atomic spectra. In my introduction, I am talking about the history of Planck's constant, ...
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1answer
67 views

What would the effects be on the world if light slowed down? [duplicate]

It would be really helpful if the effects were just given in a list form so I can research them. The reason why I am asking this is because I to write an essay regarding the effects of a change in a ...
3
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1answer
138 views

How to derive $c=1/\sqrt{\varepsilon_0\,\mu_0}$ from integral form of Maxwell equations? [closed]

I've read similar questions and answers given thereto but find them unsatisfactory. So please don't mark my question as "duplicate". The question may as well be a duplicate, but it's still waiting for ...
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2answers
128 views

A theoretical limit of accuracy?

Is there an agreed upon/conjectured theoretical limit to our ability to resolve the accuracy of time?
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0answers
43 views

Faradays constant determination? [closed]

I am a bit confused on how faraday determined his constant. So I’ve been taught that he realized that if you sent a certain amount of charge (96485 C), then one mole (or some fraction of that based on ...
1
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1answer
76 views

How do fundamental constants determine the size of material bodies? [duplicate]

The size of an object depends on the size of the molecules and atoms it is made of and these ultimately depend on the value of the fundamental physical constants. The simplest example could be the ...
0
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1answer
116 views

About the fine structure constant value

In the PARTICLE PHYSICS BOOKLET, Extracted from the Review of Particle Physics, we read that the fine structure constant has a value $\alpha \approx 1/137$ at $Q^2=0$ and $\alpha\approx 1/128$ at $Q^...
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1answer
44 views

How to deal with constants on computer simulations? [closed]

I'm beggining learning about natural simulations on my courses and I had a few questions about time, and especially with the game "Universe Sandox²". I know about the basic Newton's formulas about ...
0
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4answers
192 views

Is the fine-structure constant related to the size of the observable universe?

The fine-structure constant $\alpha \approx 1/137$. In Planck units, this is also the charge of the electron squared, $e^2 = \alpha$ ($e \approx 0.085$). In Planck units the size of the observable ...
0
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0answers
55 views

After the redefinition of the units of fundamental physical quantities in 2019, will an uncertainty incur in the Universal constants values?

I am specifically interested in the following constants because being a student these are some of the most common constants that I face: $R$ (universal gas constant) Stefan constant Permeability of ...
0
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3answers
86 views

Newtonian gravity equation / Big $G$; not duplicate from search results

EDIT: I apparently need to rewrite this from the RE's, but I'll leave it for continuity sake. Please read my replies for my point/question clarifications. There are several threads regarding big G ...
0
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1answer
73 views

Van der Waals constant $b$ (real gas) chemical form. only

http://www2.ucdsb.on.ca/tiss/stretton/database/van_der_waals_constants.html I don't understand how to calculate exact constant - b, given only the chemical formula and nothing else. Q: T || F --- ...
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2answers
74 views

Is gravitational constant a rational number? [duplicate]

The question is the title. But I'm quite doubtful if this question is meaningful or not. Since this constant is obtained by experiment, we can never know its exact value, unlike $π$ or $e$. Is it ...
0
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1answer
42 views

Spatial variation in the fine structure constant

An article in Time (I saw it reprinted in Medium), and questions on this site discuss observations that suggest that the fine structure constant might vary spatially in the universe. If true, wouldn't ...
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2answers
55 views

How was the value of vacuum permittivity originally found?

The vacuum permittivity appears originally in Maxwell's equations, used to describe electric fields. The permeability of vacuum was defined using Ampere's force law (itself derived from Biot-Savart ...
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3answers
106 views

How fine of grain size will it take to cover a football field?

There is a claim in health circles that a single Tablespoon of Bentonite clay has enough surface area to cover a football field. Let's assume a heaping tablespoon. If you halve a (roughly spherical) ...
2
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1answer
59 views

What is a good site to use for finding physical constants at times when NIST web resources are affected by government shutdowns?

There are multiple resources for finding physical constants (say, particle data, atomic spectra, or even special-function identities) which are generally hosted by NIST, and which form essential ...
2
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0answers
131 views

Why $\kappa = 8 \pi G$ in $D$ dimensional spacetimes?

Probably another question without an answer! ;-) In most books/papers I saw on General Relativity, everybody writes $\kappa = 8 \pi G_D$ in the right part of Einstein's equation, even for spacetimes ...
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0answers
76 views

Natural classification of fundamental constants of Nature

I was wondering about the fundamental constants of Nature since several years, and still pondering on them. Of course, I have read a lot of papers on them, but never found any satisfying ...
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0answers
46 views

General question about making differential equations dimensionless

Suppose you have a set of differential equations that you wish to normalize/make dimensionless. From what I've seen, you can usually use dimensional analysis to figure out a good choice of constants ...
1
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1answer
159 views

How can a Lego version of a Kibble balance measure the Planck constant?

As the picture shows below [][1] in a Kibble balance, one can drop out the measurement uncertainty of $B$ (magnetic flux intensity) and $L$ (length of coil) by the use of two modes, force mode and ...
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2answers
83 views

Can we set cosmological constant equal to one?

People often say that the cosmological constant is too small. $\Lambda=10^{-120}$ in Planck units. Can we set $\Lambda=\hbar=c=1$ ? If so what would this give for $G$, the gravitational constant in ...
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1answer
60 views

Constants of proportionality in Force Equations/ Physics in General

I was in physics class and we were talking about the gravitational constant G (6.67 x 10^-11 Nm^2/Kg^2). The question came up: "Why does $F= (GMm)/r^2$ have a constant of proportionality and not $...
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1answer
517 views

Can a physical quantity be of different dimensions depending of the system of measurement?

When comparing the Wikipedia articles on the International System of Units, the Planck unit system, and the geometrized unit system one question arises: can a physical quantity be of different ...
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1answer
92 views

Is the uncertainty principle a circular argument? [closed]

Uncertainty is due to the measurement techniques humans tend to use requiring photoelectric effect. The Planck constant is due to the photoelectric effect. If the standard deviation of measurement was ...
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3answers
582 views

Why does the fine-structure constant $α$ have the value it does?

This is a follow-up to this great answer. All of the other related questions have answers explaining how units come into play when measuring "universal" constants, like the value of the speed of ...
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1answer
57 views

What does the universal gas constant, $R ,$ represent?

What does universal gas constant represent? My textbook says: it is the energy required to raise a ideal gas by 1K The Mayer formula is $$ C_{\text{p}} = C_{\text{v}}+R \,,$$ so isn't text book ...
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1answer
75 views

In the value of gas constant $R$, what kind of mole is it?

Wikipedia gives $$R=8.3144598(48)\, \rm J\,mol^{−1}\,K^{−1}$$ But I want to ask how is it possible to write $\mathrm{mol}$ without a suffix? I mean, we must determine if we have $1\ \mathrm{mol}$ of ...