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2answers
290 views

Sommerfeld Parameter Confusion

In almost every reference site I can find, the Sommerfeld parameter $\eta$ is explicitly stated as $$\eta=\frac{Z_1Z_2e^2}{\hbar \nu}=\frac{Z_1Z_2e^2}{\hbar }\sqrt{\frac{\mu}{2E}}$$ Where $Z_1$ and $...
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1answer
3k views

$\Delta T$, temperature units. How to use fahrenheit in this formula

To calculate the power in a fluid with a flow, the following formula is applied: $$P = \Delta T \rho c_p \times flow$$ $\Delta T$ can be entered as both Kelvin and Celsius. But what if I want to use ...
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1answer
69 views

What units are needed for the variables when I want the result to be in $erg$ [closed]

$erg$ is an Energy unit, which means that it is equal to $\frac{mass{\cdot}distance^2}{time^2}$. If I want to calculate the kinetic energy of a body in erg units, in what units should the distance and ...
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1answer
243 views

Clarification on factors of $c$ in the Lorentz' force

I was told that Lorentz' force is given by $${\bf F}= q{\bf v} \times {\bf B}.$$ But I have read that it is given by $${\bf F}= \frac{q}{c}{\bf v} \times {\bf B}.$$ Why have these two relations ...
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1answer
944 views

Converting Notes to Milliseconds

Given a note duration (whole, half, quarter, etc.), a tempo (in beats per minute), and a time signature, how long does that note last in milliseconds?
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1answer
63 views

Units in gravitational N-body simulations

I use a code in Python to simulate a binary system interacting through gravity. You can find it here; The code works fine. I am however having problems with the units of length and velocity. I ...
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1answer
93 views

If Coulomb and Esu have different dimensions, why can we convert simply by 1C= 3*10e9 esu?

I was always told in school we cannot convert an apple into a potato, so we have to have the same dimensions on both sides. When converting coulomb to esu, we do not seem to bother with dimensions. ...
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1answer
390 views

Difference between kilogram-force and kilogram

I know that a 1 kilogram-force is the force of 1 kilogram acted upon by 1 standard unit of gravity (9.80665 m/s^2). However, in torque descriptions I find that some use $kgf*cm$ while others use $...
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2answers
407 views

Numerically solving 2D poisson equation by FFT, proper units

The 2D Poisson equation is: (1)$$\frac{d^2\varphi(x,y)}{dx^2}+\frac{d^2\varphi(x,y)}{dy^2}=-\frac{\varrho(x,y)}{\epsilon_0\epsilon}$$ And in $k$-space it is in form of: (2)$$(k_x^2+k_y^2) \phi(k_x,...
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1answer
1k views

Photometer: measured Irradiance L converted to photon rate

I am conducting an experiment in which the power meter reading of $410\,nm$ narrow bandpass stimulus is noted to be 30 $\frac{\mu W}{cm^2}$ at a distance of 1 inch away from the light source. I wish ...
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1answer
336 views

Conversion of the units BeV (US) and GeV (UN)

What is the difference in the definition of a billion electron volts in United states (US) and United Nations (UN)? When the US people say billion, do they mean $10^{12}$ or $10^9$?
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1answer
102 views

dynamic viscosity in the minute scale

The dynamic viscosity of air is $1.78\cdot 10^{-5}Pas = 1.78\cdot 10^{-5}\frac{kg}{ms}$. How do I convert this to the minute scale? I see a reason for multiplying the value with 60 (because of the $\...
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0answers
18 views

Conversion from PPBV to PPBM [closed]

What is the conversion between PPBV and PPBM? I have a database that includes values of Parts-per-billion-by-volume (PPBV) as a function of altitude. I've been asked to convert this to "parts-per-...
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0answers
39 views

Sudbery's Quantum Mechanics and the Particles of Nature, Chapter 1, Problem 2: Calculate the mass of the electron [closed]

I'm currently working on the problems for Chapter 1 of Quantum Mechanics and the Particles of Nature: An outline for mathematicians by Anthony Sudbery (Cambridge University Press, 1986; reprinted (...
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0answers
69 views

What unit system puts a bunch of powers of ten in Maxwell's equations?

In what unit system can we get the Maxwell equation in the following form (section 1.2 from Lewin's book Advanced Theory of Waveguide) $$\nabla\times \vec E = -10^8\mu \frac{\partial \vec H} {\...
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1answer
684 views

How to derive velocity pressure in English units?

I know that velocity pressure can be calculated from dynamic pressure according to the potential energy of pressure (from Bernoulli's equation): $$ P = \frac{1}{2} \rho \overline{V}^2 $$ where P = ...
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1answer
112 views

Calculating charge density

When calculating uniform charge density, I yielded a solution with units: $$VC^2 / Nm^2$$ The answer is telling me that this is equivalent to: $$C/m^2$$ where: $$m : meter$$ $$C : Coulomb$$ $$V : ...
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1answer
53 views

Pressure equation working to get units kg m/s$^2$, but stuck?

Why does $kg/m^3 \cdot m/s^2 \cdot m$ become $kg\,m/s^2$ (i.e. one newton) When I do the working, I get $kg/(s^2 m)$ (i.e. metres is on the bottom rather than the top) My working is: \begin{align} ...
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0answers
22 views

How to understand/derive Eq 5.5 in Geiner's Quantum Mechanics - An Introduction?

Geiner's Quantum Mechanics - An Introduction has an unnumbered equation above Eq. 6 in section 2.4 discussing density -- not sure if it is energy density -- of radiation: ... $$dE/dV = E/V =a T^...
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0answers
80 views

Geometrised Units

I am curious as to how to express a area units in geometrised ones. I was reading on wikipedia and saw that when angular momentum is converted into geometrised units, it is expressed as a dimension of ...
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0answers
72 views

Noise of a fiber optic gyro

I have not much experience with noise handling or calculations, furthermore in my researches couldn't find a similar problem, so here is my attempt: Having a fiber optic gyro that is rated with a ...
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1answer
118 views

Unit Conversion [closed]

I need to convert this expression $ 81752 \left( \frac{BTU}{in^2 h ºR} \right )$ to $ \left( \frac{Kg}{s^3 ºC} \right )$ Is my draft correct? $ 81752 \left( \frac{BTU}{in^2 h ºR} \right ) \...
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0answers
192 views

Galaxies and projected radius vs arcmins

I have two sets of data (globular clusters), one for the Andromeda Galaxy and one for the Milky Way. I want to compare the distribution of globular clusters between the two galaxies according to ...
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1answer
532 views

noise level (units confusion)

i had a question in one of my classes regarding SNR in underwater acoustic channels. There are a couple of terms with the unit dB re uPa. I know it stands for dB ...
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0answers
1k views

FPS to MKS usage issues

I'm currently taking a high school physics class and we're doing friction problems now. I've been doing the ones that use MKS perfectly well, but when the problems start to use the FPS system, I'm ...
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8answers
7k views

Celsius to Fahrenheit confusion: why there is no 1 to x ratio?

Why is it not possible to know the ratio of 1°C to how many Fahrenheit and use that to convert from or to Celsius/Fahrenheit? What is really happening? Fahrenheit increases linearly and so does ...
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3answers
545 views

100°C = 100 K =?

I'm in first year. Our class is in lesson " Heat and Thermodynamics". While solving a numerical problem of a reversible engine he told us that 100 degree Celsius is equal to 100 kelvin. I inquired but ...
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2answers
2k views

Why does $E=mc^2$ give results in Joules?

Why does $E=mc^2$ give results in Joules ? Why didn't Einstein need to create a separate unit and how come using two standard units (speed of light in km.s and mass in grams) give another result in ...
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3answers
135 views

Proper way to write the units to indicate that they include an offset?

Past a certain point of complexity, I get rather confused with physical units, so I am asking a physicist for help. I have a code that represents temperature, with a resolution of [0.5 °C], whose ...
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2answers
100 views

What is $c$ in the Lorentz force expression?

The usual Lorentz force expression I am familiar with is this: $$\vec F=q(\vec E+\vec v \times \vec B)$$ I have seen some other versions lately that include an extra factor $1/c$: $$\vec F=q\left(\...
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2answers
194 views

How many psi's are in one bar?

6894.7573 bar = 100000.0 psi according to google 6894.7573 bar = 100000.0001 psi according to wolfram alpha which is it? How many psis are in one ...
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3answers
70 views

Displacement based on acceleration in km/h$^2$

For calculation of displacement based on acceleration and time, I have the formula below: $$ x = v_0t + \tfrac{1}{2}at^2 .$$ If I get $a$ in km/h$^2$, and $x$ in km and $v_0$ in km/h and I suppose ...
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1answer
5k views

How does (kg/m^3) * (m/s^2) * (m) come out to be units of N/m^2? [closed]

To me it seems to come out to be kg/(m*s^2). Is this somehow equivalent to N/m^2?
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6answers
65 views

The Kelvin-Celsius problem

Let's suppose we have temperatures 30°C and 35°C. Converting them to Kelvin we have 303.15K and 308.15K. In the second case, the temperature difference is 5K. While in first case, temperature ...
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1answer
82 views

Converting $F^2$ to $C^2$

I'm trying to convert Fahrenheit squared $F^2$ into Celsius squared $C^2$. I know how to convert a value $x$ in $F$ into $C$ with: $\frac{5}{9}(x - 32)$ I also know how to convert a value $x$ in $...
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1answer
244 views

Dimensional Analysis in Electromagnetism (SI vs Gaussian-cgs)

Looking at Konopinski's formula for conjugate momentum (in the comment after equation 3 of "What the Vector Potential Describes"): p = M v + q A /c it is plain enough that M v is momentum, but if we ...
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2answers
57 views

Significant error conversion

So here is my question: Say we have measured something to be 15,67 mm and the significant error is $\pm 0,01$mm. then we convert the measurement to meter to be 0,01567m would the significant error ...
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1answer
3k views

I need some help trying to convert the specific fuel consumption from imperial to metric units

Ok the imperial unit for the specific fuel consumption for a jet aircraft is shown below. Its the amount of fuel (in lbs) per hour required to produce 1 pound of thrust. $$\frac{\frac{lbs}{h}}{lbs}$$ ...
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1answer
450 views

if a force is 1 newton metre, what is it at 2 meters?

If I have a force, say 24 kg/cm what would that equate to at 2cm? I would like to know the formulae for calculating this. For example. If a motor can hold an object of 24kg at 1cm from its pivot ...
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2answers
46 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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1answer
47 views

Fine structure constant and unit conversion [closed]

In a paper I'm reading, the author writes down the following formula: $$\Gamma=\dfrac{\alpha^2}{576\pi^3}\dfrac{\left(4+z\right)^2}{z}\dfrac{m^5}{m^2_\pi f_\pi^2}$$ $\Gamma$ is a function of $m$ (in ...
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1answer
36 views

Classification of plane angle as fundamental or derived

I recently started with my high school studies and the chapter I am stuck at is units and measurements. I was told about two types of physical quantities and my teacher gave me the following ...
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2answers
55 views

Bohr's model and positronium

I was trying to get an order of magnitude estimate for the radii and energies of positronium using the Bohr's model. I did find a few places where they have used the reduced mass to replace the ...
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2answers
271 views

If a propane torch is rated at 200,000 BTUs, what does this translate to in terms of joules/second?

If a propane torch is rated at 200,000 BTUs, what does this translate to in terms of joules/second? Not exactly a physics question per say, but it falls in the realm. How do I convert/understand ...
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1answer
64 views

Constant $c$ in Lorentz force [duplicate]

I met some of examples of force in studying classical dynamics, and Lorentz force was represented as $$ \mathbf{F}=\frac{q}{c} \mathbf{\dot{r}} \times \mathbf{B} $$ I've searched for meaning of $c$, ...
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1answer
93 views

A Conversion problem featuring Significant figures [closed]

What is the speed of a car going v=1.000 mile per hour in SI units? You can do each conversion separately. Use the facts that 1mile=1609 meters and 1hour=3600 seconds. Express your answer in meters ...
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2answers
332 views

Unit conversion from km to mm [closed]

I'm a bit rusty on my unit conversion skills and I need help figuring out what I did incorrectly converting 9.06 x 10^8 km into mm. Here's what I did: 9.06 x 10^8 km x (1 meter/10^3 km) x (10^-3 km/1 ...
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1answer
171 views

Magnetic Field and the Speed of Light

Is it just a historical choice that both magnetic field and the Lorentz force equation include the speed of light? I figure that whoever wrote up the equations (in cgs!) could have put both factors ...
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1answer
740 views

CGS Units to SI Units

This may be a stupid question but I am having trouble getting the same result in CGS units as I would if I used SI units for a unitless calculation. I have to calculate $E_c=\frac{m_e c\, \omega_c}{...
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1answer
959 views

Natural Units and the Nuclear Radius

In a paper I'm looking at and also in a similar program, the authors note that the nuclear radius $R$ is given in "natural units" as $R = 3.11\times 10^{-3}\;A^{1/3}$. This has me slightly confused, ...