Questions tagged [unit-conversion]
291 questions
20
votes
3 answers
Physical dimensions for the Coulomb force in SI and CGS
The Coulomb force in SI units reads $\displaystyle F = \frac{1}{4\pi\varepsilon }\frac{Q_1\times Q_2}{R^{2}} $.
On the other hand, in CGS this reads $\displaystyle F = \frac{Q_1\times Q_2}{R^{2}} $.
Why is this? I mean, doesn't it make any…
S L
- 1,591
14
votes
3 answers
Isn’t natural units prone to mistakes?
Suppose I am deriving a length contraction formula using natural units. If I arrive at $L = L_0 \sqrt{1 - v^2}$, I know that I should divide $v^2$ by $c^2$ to get the correct answer in SI units. But what if I mistakenly forgot to square the velocity…
Atom
- 145
12
votes
2 answers
Higgs Boson mass in Electron volts?
Im no physics genius here, I was just interested in the Higgs Boson so I was reading this article : How the Discovery of the Higgs Boson Could Break Physics
I came across this
Furthermore, all indications are that scientists will find that the…
Ashu
- 261
11
votes
3 answers
Coulomb's Law: why is $k = \dfrac{1}{4\pi\epsilon_0}$
This was supposed to be a long question but something went wrong and everything I typed was lost. Here goes.
Why is $k = \dfrac{1}{4\pi\epsilon_0}$ in Coulomb's law?
Is this an experimental fact?
If not, what is the significance of this…
Ron
- 532
9
votes
3 answers
How to properly understand Gaussian Units?
I have trouble understanding Gaussian Units in relation to SI units: $1/c$ factors seem to appear almost at random, while other constant such as $\varepsilon _0$ or $4\pi$ disappear with seemingly comparable randomness.
The related Wikipedia page is…
Noumeno
- 4,703
8
votes
2 answers
Converting between brilliance, intensity, and flux
This one should be a bit of a softball, but I can't find it explicitly stated anywhere on the internet, and my basic unit analysis doesn't seem to work.
Suppose you have a beam of synchrotron radiation with a brilliance $B$ at a given energy. (For…
8
votes
2 answers
Where does the joules come from (ideal gas constant)?
I have not done any physics in ages and have recently started studying it. The first chapter in my book deals with the ideal gas constant:
$$pV=nRT$$
It is rewritten as:
$$R=\frac{pV}{nT}$$
When I write it in SI units, it looks like…
Gobabis
- 392
8
votes
2 answers
How to recover units?
Theorists frequently use convenient units like $\hbar=1$ or $m=2$ or whatever is useful to simplify the notation in the problem. And after all the calculations are done the units are recovered based on what the unit of the answer needs to be.
I can…
ftiaronsem
- 1,643
7
votes
1 answer
Magnetic susceptibility in 1/eV
In this paper the authors refer to
transverse susceptibility $\chi_{ \perp}$ [meV $^{−1}$]
I was taught that the magnetic susceptibility is dimensionless.
How do I get $\chi$ in the above units??
Pie86
- 313
7
votes
4 answers
How can you calculate (or convert) the $\rm Wh$ of a capacitor whose energy is given in Farads?
When trying to compare the energy in a battery to the energy in a capacitor, the units don't match up. How can one compare a battery whose Ah are 10 and Voltage is 3 (for a total of 30 Wh) to a capacitor whose Farads is X and voltage is Y?
Jack Dagmy
- 189
7
votes
3 answers
What is the relationship between the magnetic units oersted and tesla?
How are the units oersted and tesla related? For example, how would you express $20\:\mathrm{Oe}$ in tesla?
Ganesh
- 200
6
votes
2 answers
Relationship between measures of light (candela and lux)
I am trying to understand the relationship between two measures of light: lux and candela. It is probably easy for those with longer experience, but here it goes:
I have learnt (here for instance) that lux equals candela per square meter. But this…
user2078515
- 359
6
votes
1 answer
How is formula for converting pressure from mmHg to Pa derived?
Today my younger brother asked me from where does the 1 Pa = 0.00750061683 mmHg formula for mercury barometer come. He needs a way to derive it, or an academic source which can be cited.
After doing some calculations we got the formula for a…
AndrejaKo
- 162
6
votes
2 answers
CGS Units for Magnetism
Why does the formula for magnetic field force include the speed of light in the denominator in cgs units? Where does the extra $c$ go in SI units?
user24082
6
votes
1 answer
How to convert cm$^{-1}$ to eV?
I know that $1 \:\mathrm{cm}^{-1} = 8065.54429 \:\mathrm{eV}$.
I know that wave-number has unit $\:\mathrm{cm}^{-1}$ and that $E=hc\times \mathrm{wavenumber}$.
But how do I arrive to the number $8065.54429$?
I know how to make the conversion but…
Filip Landgren
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