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Questions tagged [unit-conversion]

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1answer
52 views

Correct form of Lorentz force equation [duplicate]

When I was reading the first volume of the theoretical minimum by Leonard Susskind, I encountered upon this: But when I checked Griffiths and all my other electricity and magnetism books, it showed $...
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2answers
79 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 ...
0
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1answer
44 views

Is there a general algorithm for conversion of units?

I'm not exactly sure where the best place to put this, as it's more of a general question about dimensional analysis. I decided I was tired of having to convert units all of the time, and was not ...
1
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2answers
63 views

Conversion from Planck unit to SI [closed]

Good evening, I'm reading the paper Prehawking radiation by William G. Unruh where it says: ...a time scale of order of $m^{3}$ in Planck units, or $10^{53}$ ages of the current universe for a ...
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3answers
61 views

What are the units of time when planck's constant is equal to 1?

If I express a Hamiltonian $H$ in units of Hz by dividing the energy terms in the Hamiltonian by hbar $\tilde{H}=\dfrac{H}{\hbar}$ which means you set $\hbar =1$. Then what are the units of time? Also ...
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1answer
34 views

Issue in conversions from force to mass units

I have a problem converting force to mass units, in this example for 9.81kgf: To get the mass, dividing by gravity, I get 1kg ...
0
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1answer
59 views

Conversion between mass units

I am enrolled in a course related to physics, and converting between mass units is so tricky for me. I always treat in my work only in SI units and maybe MKS units, at level of weights, I find it easy....
0
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1answer
30 views

How do I convert $W/(mK)$, $W/m^2$ and $W/(m^2K)$ to the same “dimensionality” and unit?

How do I convert $W/(mK)$, $W/m^2$ and $W/(m^2K)$ to the same "dimensionality" and unit? $W/mk$ is thermal conductivity. $W/m^2$ is heat flow density related to one unit. $W/m^2k$ is heat transfer ...
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1answer
78 views

I'm confused about electric flux?

In a previous physics class, I learned that the electric flux was $\vec{E}\cdot\vec{A}$ (dot product), and hence the unit is $Nm^2/C$. But in my electromagnetics book, it says the unit is Coulomb, and ...
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1answer
60 views

Intuition about the congruence of readings of Celsius and Fahrenheit scales at -40°C [closed]

At -40°C temperature, the Fahrenheit scale also shows -40°F. But how is this ever possible? They are two different scales! What's the intuition behind this?
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0answers
38 views

Geometrized units in Wald

I am trying to follow a derivation in this paper from Wald Specifically, at the end of the paper, just under Eq. 4.7 there is given the equation $$ Q/m \leq 2 B_0 m$$ where $Q$ is the system ...
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1answer
243 views

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 $...
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1answer
36 views

Pressure unit computation (feet of mercury, but applies also to foot of water..) [closed]

Grr this question makes me crazy. Here you can see that ftHg = 13595.1 kg/m3 × 1 ft × ɡ0 = ≈ 4.063666×104 Pa. (= 40636.664 Pa) https://en.wikipedia.org/wiki/Conversion_of_units (Pressure or ...
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3answers
116 views

Magnetic $H$ field unit in cgs system

I'm studying an old E&M textbook which uses cgs unit system. I'm re-writing the formulas in SI unit. The book says $\vec{H}=\vec{B}-4\pi\vec{M}$. So I guessed that $H$ should have same unit as $...
0
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1answer
52 views

Need help in calculating the pull on string in kgs when moving weight on horizontal bar

need your help. I realized today, if you do not practice it becomes hard to understand simple concepts even you were once a science student :( I have attached a picture to help make the problem ...
0
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4answers
76 views

Converting part of a compound unit

I am working with several different datasets with different units. I want to convert the distances to mm for comparison. The units I'm dealing with are $\mathrm{kg/m^2/s}$, $\mathrm{mm/day}$, and $\...
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1answer
1k views

How to convert bars to meters head?

I am trying to convert 1 bar to meters to come up with a conversion factor. Thus, 1 bar = x meters head What is x? From my computations I got something like ...
0
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1answer
188 views

How can I convert spectral irradiance to spectral radiance [closed]

I have information on the spectral irradiance incoming from the sun at the top of the atmosphere in units of $\rm mW\ m^{-2}\ nm^{-1} $. The photons hit a hypothetical surface on the earth with 0.3 ...
0
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0answers
17 views

Finding the generated magnetic field of a Hall generator

I've been using a Hall generator to generate a particular magnetic field by applying a current. I need to work out what field this corresponds to in Tesla. All I have to go on is what's in the photo ...
2
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1answer
161 views

Why does $\frac{1}{4\pi}$ appear in many formulas? [duplicate]

Why do most of the physical equations have $\frac{1}{4\pi}$ as constants? I have seen that many equations have $\frac{1}{4\pi}$ as constants like Coulomb, pendulum problems, etc. Can anyone tell me ...
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1answer
45 views

Laser beam diameters: What are the units of 1/e^2?

I own an argon ion laser head with a beam diameter of '0.70' (using $1/e^2$ width). What is the unit on the 0.70? And can it be converted to something more intuitive, such as meters?
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1answer
39 views

Converting units of $G$ [closed]

I want to convert $G$ from $\rm m^3 \:kg^{-1} \:s^{-2}$ to the units $\rm km^3 \: kg^{-1} min^{-2}$. How can this be done? I want to know what $6.67\times 10^{-11} \:\rm m^3 \:kg^{-1} \:s^{-2}$ is ...
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0answers
26 views

Dimension scaling of a model hamiltonian system?

I have a model 2dof double well potential Hamiltonian given as $$H = P1*P1/2 + P2*P2/2 + V(Q1,Q2) ,$$ where $$V(Q1,Q2) = -2*Q1^2 + Q1^4 - Q2^2 +Q2^4 +0.4*Q1*Q1*Q2*Q2 ,$$ there is no units are ...
0
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1answer
30 views

Thermal Conductivity Conversion

I need to convert a thermal conduction unit W/m.K to Btu/ft.h.°F. I have 400 W/m.K and I ...
1
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0answers
134 views

Are Heaviside-Lorentz unit and Gaussian unit natural units?

I am studying electromagnetism and have encountered the Heaviside-Lorentz unit and Gaussian unit. In these unit systems, the constant $c$ keeps occurring. For example, the Maxwell equations are of ...
0
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1answer
333 views

How to convert from an arbitrary set of units to the desired set?

I'm having trouble solving this Physics question with "made up" units. Here is the problem and my work so far. The Omicronians have told you that they use the units: $$\\{OP=7.29\frac{flurg}{grom^2}}...
0
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1answer
30 views

How I transfer (ohm*cm)^(-1) units for conductivity into Gaussian units (s^(-1))?

I have tables for conductivity of various material in (ohm*cm)^(-1) units. How I transfer those data into Gaussian units (s^(-1))? Just a coefficient will do....
0
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1answer
109 views

Why aren't Faraday's law of induction and Maxwell-Ampere's law symmetric? [duplicate]

I don't see Faraday's law of induction and Maxwell-Ampere's law are totally symmetric in the sense that Maxwell-Ampere's law has a factor of $ϵ_0μ_0$: \begin{align} \nabla\times\mathbf E&=-\frac{\...
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1answer
47 views

Really weird question about unit analysis

Hi guys this is quite an interesting question I have because there appears to be two correct answers. There is an equation described by: $$ Pt = mC_\mathrm{mass}T+m_\mathrm{water}C_\mathrm{water}T+...
0
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1answer
34 views

Converting volume to dimensions

Not sure if this is better posted in mathematics, but I'd like to know the formula used to convert cubic meters to dimensions (eg: 1m height x 1m width x 1m length). I understand that you can turn ...
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0answers
58 views

Wierd form of Gauss law

I ran into a problem while reading a book on electromagnetism. It is a strange form of Gauss law. $$\int _{S} \textbf{E}\cdot d\textbf{S} = 4 \pi q$$ as opposed to the regular: $$\int _{S} \textbf{E}\...
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0answers
42 views

Clarify the meaning of the expression in my book $qq'\Leftrightarrow k_cQQ'$

My book says in electrostatic system, coulomb's law is: $F=\dfrac{qq'}{r^2}\hat{r}$ and in SI: $F=k_c\dfrac{QQ'}{r^2}\hat{r}$ It also says: $qq'\Leftrightarrow k_cQQ'$ Now what does this last ...
0
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1answer
43 views

$k_e$ (constant of Coulomb force) is sometimes seen in calculations for atomic radii and sometimes not

One of our formula for radius of atom was $\frac{n^2h^2}{4\pi^2me^2}$. And another one was, $\frac{n^2h^2}{4\pi^2me^2K}$. For hydrogen, Why $k_e$ is sometimes included and sometimes excluded ?
3
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1answer
97 views

Finding a substitution of $\mu_0$ to convert from SI to c.g.s in EM laws [closed]

In c.g.s, we set $$k=\frac 1{4\pi\epsilon_0}=1$$ which gives $$\epsilon_0=\frac 1{4\pi}$$ This conversion works, for example, in Gauss' law: in SI $$\vec{\nabla}\cdot\vec{E}=\frac\rho{\epsilon_0}$...
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3answers
710 views

Why is 1 newton meter=.225 lbs force?

This is a general question regarding force (mass x acceleration). I understand 1N =1kg mass x 1 m per second sq) all this basically tells me is that the force is proportionally increased and ...
0
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1answer
507 views

Converting lux to watts with known wavelength

I was wondering if there was a possible way to convert lux to watts accurately if the wavelength is known. I know that for the sun there is an approximate conversion of 0.0079W/m$^2$ per Lux using ...
0
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1answer
115 views

Electromagnetic Dirac equation in CGS units

The Hamiltonian of the Dirac equation in with an electromagnetic field in SI units is $$H=\gamma^0\left[ mc^2+c\gamma^k\left( p_k-\frac{q}{c}A_k \right) \right]+qA^0$$ (from https://en.wikipedia.org/...
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3answers
803 views

Velocity squared in natural units

I encountered a mental block in my understanding of natural units. According to natural units, $c = 1$, which would imply that if we wanted to convert velocity from SI units ($m/s$) to natural units (...
-1
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1answer
250 views

Why are ft-lbs used to describe muzzle energy? And how do you work with it?

Whether it's kicks, punches, or bullets, people use ft-lbs or joules to describe kinetic energy. But how is this useful? Why use torque to describe linear motion such as a bullet? And how does one ...
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1answer
163 views

How do I convert natural/Planck units to SI? [closed]

I am looking at a paper which has set: $\beta=1/kT=1$ where k is the Boltzman constant. It uses natural planck units ie $m=\hbar=k=1$. Does it make sense to extract a temperature $T$ and mass $m$ ...
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4answers
203 views

How can I change our units so that Newton's gravitational constant is $G=1$?

I'm just wondering if you can change our arbitrary values for , say, the kg, meter, or newton so that G=1 instead of 6.67x10^-11
0
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1answer
176 views

What are the actual electromagnetic units in the FPS system?

So I've been reading this Wikipedia article, and I came across the cited note that someone has derived the electromagnetic units for the FPS system. However, I can't find that publication so does ...
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1answer
207 views

Converting 1 Kelvin into eV

I am using $E=\frac{3}{2} kT$ to find the equivalent of 1 K in eV using $k=1.38\times 10^{-23} \,\mathrm{\frac{J}{K}}$. I get $E= 1.29 \times 10^{-4} \,\mathrm{eV}$, but Wikipedia says it's $8.6\times ...
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1answer
417 views

How does one convert spectral radiance from $\mathrm{(W\: cm^{-2} \: sr^{-1} )/ nm}$ to $\mathrm{ (W \:cm^{-2} \: sr^{-1} )/ cm^{-1}}$? [closed]

How does one convert spectral radiance from $\mathrm{(W\: cm^{-2} \: sr^{-1} )/ nm}$ to $\mathrm{ (W \:cm^{-2} \: sr^{-1} )/ cm^{-1}}$? The first one is the radiance represented by wavelength and ...
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2answers
73 views

Semantics: Unit/second versus unit-second [closed]

I've been trying to make sense of an unusual bit of mathematical and notational semantics in my electrical engineering studies: Velocity is typically given in units of metres per second ( $ v = \frac{...
3
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4answers
498 views

How to express an energy in natural units

If I have some angular frequency e.g. $\omega [\text{rad } \text{s}^{-1}]$, I can easily express this as an energy as $E = \hbar \omega [\text{ J}]$. Now suppose I am working in Natural (Planck) ...
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1answer
52 views

How many calories are burned by lifting 80 kilos once?

After some calculations i figured it was something like 192 kilocalories but it sounds a bit too much so im not sure if i did the right calculations. What i did was calculate the work and then convert ...
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1answer
60 views

radius unit in Pressure vs radius graph

In the TOV equation of state of neutron star if we take central pressure and central energy density in Mev/fm^3, then in what will be the unit of radius in the graph of pressure vs radius. Usual we ...
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1answer
47 views

Is the given unit conversion possible? [closed]

I have to convert from Joule to Newton than to a specific unit, but I don't know which two unit factors I have to choose (since I am not allowed to change $kg$) to get the final result: $$1\,{\rm J} ...
1
vote
1answer
176 views

Prove gravitational constant $G=1$ in geometric units

I've seen that often geometric units are defined by setting $G=c=1$, however, I have been working with a different definition, namely, to multiply time in seconds by $c$ so that it's measured in ...