Questions tagged [unit-conversion]

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685 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 ...
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1answer
155 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
1k 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 (...
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1answer
454 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
194 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
295 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
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1answer
242 views

What are the actual electromagnetic units in the foot-pound-second (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
310 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
624 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
77 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{...
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4answers
662 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
57 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
80 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
61 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} ...
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1answer
227 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 ...
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1answer
410 views

Value of gravitational constant $G$ and speed of light $c$

In an Tolman Oppenheimer and Volkoff (TOV) equation of state for static equilibrium stars, if any one want to calculate pressure and density in $\mathrm{MeV/fm^3}$, then what is the appropriate choice ...
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1answer
197 views

How do I convert Nm/Kg in MGOe? [closed]

i have to buy a few magnets of a certain attraction intensity, i would like to know how to convert Nm / Kg in MGOe. What is the formula? Can you please make an example for 100 Nm/Kg?
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2answers
184 views

Conversion of compound temperature units

In general one can convert from one unit to another (of the same dimension) by using (($U$,$A$) and ($V$,$B$) being compatible unit pairs in the following) $xU=(x\ast f_{U\rightarrow A}+o_{U\...
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1answer
350 views

Values of coefficient of expansion differ,when temperatures are measured on centigrade scale and on Fahrenheit scale separately [closed]

In solving above question, it was given that Change of $5 ℃ = $ change of $9 ℉$ I only know the relation that $$\dfrac{C}{5}=\dfrac{F - 32}{9}$$ I don't know how Change of $5 ℃ = $ change of $9 ℉...
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1answer
203 views

How to convert kWh/(m^3 multiplied by degrees celsius) to SI unit of Volumetric heat capacity? [closed]

We have a project at school about making more energy efficient buildings. We are using this software called Energy3D concord. In the window where you can edit the volumetric heat capacity, the units ...
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2answers
100 views

Why dont low density objects like nylon not fly into the air with more density?

According to this Website Nylon has a density between 1.11 to 1.18 g/cm3. Air on see level has a density of 1.225 g/cm3. So why does nylon not fly into the air like a helium balloon? Sorry for this ...
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1answer
1k views

One metric second equals how many normal seconds? [closed]

I'm attempting to study for an exam on Friday and to do so I'm doing some practice problems - I got to this problem and for the life of me I can't figure out how to approach it. The problem is as ...
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4answers
283 views

Can I plug in the SI unit variants of measurement for this formula?

Here, NASA gives a formula for aircraft lift: $$ L = \frac12 d\ v^2 s C_L $$ with $L =$ Lift, which must equal the airplane's weight in pounds $d =$ density of the air. This will change due to ...
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1answer
164 views

Mass due to the ionization energy of the hydrogen atom from $E = mc^2$

Using $ E = mc^2$ I want to calculate a hypothetical mass from the first ionization energy of the hydrogen atom. The ionization energy is given in units of $\rm kJ/mol$ which could seemingly be ...
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0answers
67 views

Interpreting impulse value “c kg”

I have a small question about a physics exercise concerning the relativistic relationship between energy and momentum. The exercise says: We have 2 objects with rest mass 8 kg. We shoot the objects ...
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1answer
433 views

Units of Larmor frequency

I'm sorry if this is really basic, but what exactly is the unit of Larmor frequency? According to Wikipedia, the formula for Larmor frequency is: $$\omega = \frac{egB}{2m}$$ and with $g$ as a ...
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1answer
23k views

Converting enthalpy from J/g to kJ/mol [closed]

On some books I found values of enthalpy in J/g, on other books in kJ/mol. How could I convert enthalpy from J/g to kJ/mol? Thank you.
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0answers
35 views

In the process of probability of two flavor neutrino, how does the factor $1.27$ comes from?

Up so far I have been working on deriving probability for two flavor neutrino and have consistent results with wikipedia or textbook. But I have some trouble with deriving some factor $1.27$. \...
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2answers
163 views

How to Convert Dimension of $R$ constant of Air (J/Kg.K)?

Example) (P=nRT/V) in this equation P=nRT/V, The final dimension is achieved should be a function of pressure, But I can not understand this dimension in final (mol.J/Kg.Liter). when use in R ...
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1answer
147 views

Help with conversion from SI Units to General Relativity Units [closed]

The Book im reading about general relativity says that energy unit in GR are kg, so until i know the units of energy in the SI are Joules (J) $$ 1 J = 1 kg \frac{m^2}{...
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1answer
140 views

Is it possible to use natural units (particle physics units) with boost? [closed]

I would like to use boost to handle my units in my c++ code, and I was wondering if it was possible to use natural units? That is, can I add a mass and a momentum and set it equal to an energy without ...
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2answers
214 views

How is the unit of kinetic energy equivalent to $\mathrm{Pa}\cdot\mathrm{m}^3$?

I know that the unit of kinetic energy is Joules, J. However, the book I have says that the "unit of kinetic energy is equivalent to $\text{Pa}\cdot\text{m}^3$. I have been trying to prove this result,...
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1answer
326 views

Confusing about the unit of Fermi velocity

The unit 'eVA(angstrom)' is used in some ARPES papers for the Fermi velocity. How can I convert it to the conventional unit ‘m/s’?
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2answers
1k views

Why can't a permanent magnet's magnetic field be converted into other types of energy?

Can a solid magnet excite any type of atom's electrons to release photons? Why can't magnets be arranged to be its own generator? is there an equation for reason solid magnets can't self perpetuate? ...
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1answer
7k views

How to convert Bq/g to Sievert (Dose), and how to get values Sv/Bq?

How to convert Bq/g (Activity) to Sievert/g(Dose)? How can I get values in (Sv/Bq)? Please help, it is really confusing.
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2answers
78 views

How to infer what integrals and derivatives signify and when to take them? [closed]

So I have very little background in physics since I'm a mathematical sciences major, but upon being exposed to some physics I've had some difficulties in understanding how to infer the derivatives and ...
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2answers
773 views

Convert formula from CGS to SI

I'd like to convert this formula \begin{equation} l^2 =\frac{c\hbar}{eH} \end{equation} where $l$ is a length, and $H$ is in oersted, to SI units. I am pretty sure it uses CGS, since Oe is mentioned ...
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2answers
578 views

Is there an easy way to remember which formulas use Kelvin vs which ones use Celsius?

I know that the ones with change in temperature don't matter since the increments are the same, but I'm not sure if I can memorize which ones require $K$ and which ones require $^{\circ}C$. Is it ...
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2answers
1k views

Why are there two different SI units of magnetic charge?

Taking a look at the wiki on magnetic charge, there are two different forms of the Dirac Quantization Condition in SI units: the Weber form $$\frac{q_e q_m}{2 \pi \hbar} \in \mathbb{Z}$$ and the ...
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1answer
8k views

How to convert battery capacity mAh to watt-hour? [closed]

Many USB battery chargers will state it as 5000 mAh or 20100 mAh. Some of these batteries can charge a Macbook 12 inch notebook. On the other hand, Macbook 12 inch battery capacity is stated as ...
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1answer
2k views

How Joule/s and V*A both equal to same 1 Watt?

In physics, Watt equals to Energy per second [J/s]. But also, Volt times Amps also equals to Watt. How can one tell they both are the same Watt? How can one measure it? For example, in motors. The ...
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3answers
71 views

Capacitor's Charge

I see the formula of charge on capacitor's plate is $C=\frac{KA}{d}$, where $K$ is the dielectric constant and $A$ is the area of the capacitor. Now some sources indicate the unit of $A$ as square-...
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4answers
137 views

Deriving the correct unit of force [closed]

Take a look of the Newtonian gravity equation below: $$\text{gravitational force} = \frac{GMm}{r^2}$$ $GM$ of earth is $398600.4418\ \mathrm{km^3 s^{-2}}$. Let $m = 1000\ \mathrm{kg}$, and $r = 6378\ \...
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1answer
125 views

Calculus of Weight and mass

I am confusing about some data for calculus. First, the equivalence of weight: 1kgf=9.8N Second, the mass of 1 Newton is: 1N/(9.8m/s$^2$). And finally, to get the mass of 1kgf, I have to divide by ...
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5answers
1k views

Work as force * distance — what about mass? [closed]

So, in defining work as force * distance, how is mass applied? Is it just that it's $1kg$ multiplied in normally, but that's typically ignored / not shown? ..so: $2kg \cdot 1n \cdot 1m$ = $2J$ .....
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3answers
19k views

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?
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1answer
1k views

How to convert intensity arbitray units to percentage in a XRD data?

In powder x ray diffraction result contains mainly two values 2theta and intensity where 2theta is in degree's and intensity is in arbitrary unit ...
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3answers
2k views

Confusion on electron volt and Kelvin?

If an element A has a binding energy of X eV with element B, can it be said that it is equivalent to X*11600K as 1 eV approx equals 11600K. I do not think this is correct as temp. is linked to the ...
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2answers
556 views

What does J cm-1 stand?

For an optical component, I got following number as an optical damage threshold from the company, damage threshold = 10 Jcm-1,20ns, 20Hz It looks like 20ns is ...
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1answer
50 views

In this energy conservation problem, why are the answers different with different units? [closed]

Really basic question, but basically I'm given a change in height in centimeters (that's how I measured it). From that, I'm supposed to find the initial kinetic energy. $KE_i = PE_f$ After doing ...