Units Definition and 998 Threads

I was always puzzled by the fact that while almost all Planck units are extreme (very high or very low), Mass and Energy are exception from that rule. Planck mass is in the ‘middle’ of the spectrum, and it divides the mass spectrum into 2 parts: For small masses/energies m << Mplanck we can...

Homework Statement A mouse has an pupil diameter of 2.5 mm. lying 200 meters from the mouse are two stones 30 cm apart. λ = 500 nm a) what angle do the stones subtend? b) what is the MAR (minimum angle of resolution) of the mouse's eye. Homework Equations question a) tanθ = O/A O= 0.3 m A= 200...

Hi all, I'm working on a problem where I have to find the time it takes for a planet to form from a protoplanetary disk, using the equation: t = \frac {3}{A}M^{1/3} Where A= ( \frac {(1+2\beta)\sigma}{P}) (\frac {3\pi^2}{4\rho_m})^{2/3} However, I'm not sure which units the...

Homework Statement I am trying to get the units to match up on both sides. \frac{\partial T}{\partial t} = \frac{\nabla ^{2} T}{k} = \frac{1}{K}(\frac{\partial ^2 T}{\partial x^2} + \frac{\partial ^2 T}{\partial y^2} + \frac{\partial ^2 T}{\partial z^2}}), where k is the thermal resistivity...

Whenever I see the amplitude for fermion scattering, it comes out dimensionless. However, for scalar scattering, the dimensions are 1/energy^2. For example, for 2 particles scattering into 2 particles in a \phi^3 interaction, there is just one internal line, so the amplitude is proportional to...

Homework Statement A series RLC circuit has a resonance fre- quency of 1360/ Hz. When it is operating at a frequency of ! > !0, XL = 9.7 and XC = 9.3 . Find the value of L. Answer in units of mH. Homework Equations X(L)=w*L The Attempt at a Solution what i did is...

It seems to me that solar power and air conditioning are made for each other. As of now there are several different companies making smaller adsorption/absorption AC units, but they are overpriced compared to their electric driven counterparts giving limited return on investment. Here's what...

Tensors and Units Consistency Where do the unit labels go on tensors? This discussion is continued from this thread https://www.physicsforums.com/showthread.php?t=321298" Greg, I've been trying to make sense of things in mixed units. Taking the dot product as you've done is a good test...

What are the fundamental base units for Force and Volume? I think its cm3 for volume but not completely sure.

I've been reading a bit on vector calculus trying to get a solid grasp on it. I am wondering how it can be stated that given C=AXB (all vectors), that C is equivalent to the area of the rectangle formed by A and B in the A,B plane. How can you equate length and area. One is in say...mm and the...

Homework Statement In the ring Z[\sqrt{-3}] find all units and prove that 2 is irreducible but 7 is not. Homework Equations The Attempt at a Solution Well a unit is a non-zero element of the ring that when multiplied by some other non-zero element of the ring gives the unity of...

This is my first assignment in my Modern (Abstract) Algebra class, just to give an idea where I am with tools that I can use. Homework Statement Describe all units and zero divisors in Z[i] Homework Equations The Attempt at a Solution I already know the answers are units = 1...

I'm searching for an online text on units, units systems, dimensions, dimensional analysis and so forth. A nice overview or summary, or an introduction not geared to the complete beginner. Has anybody a good link? thank you

Homework Statement "A gas storage system contains oxygen at a pressure of 5 atmospheres at 300 K. (Here, you may assume that oxygen behaves as an ideal gas.) The volume of the cylinder is initially 150 L. (State 1.) In a fire the gas is initially heated by 200 K, with a safety system keeping...

Homework Statement Hi, I need to know the correct SI units for Einstein Coefficients (A and B) for stimulated emission (say laser). The equation I'm on about is Homework Equations \frac{A}{B} = \frac{8\pi h\nu^{3}}{c^{3}}The Attempt at a Solution after some scribbling I got to \frac{A}{B}...

Homework Statement A quantity, d, depends on the angular frequency in the following manner: d=ω C √(l/g) sin(ω K √(l/g)) Determine the units of C and K Homework Equations d=m ω= sec-1 l=m g=m/s2 I substituted this into the equation m=s^(-1) C √(m/(m/s^2 )) sin(s^(-1) K √(m/(m/s^2 )) )...

While reading a paper on optics, I came across "the radiance of the projector is 20 mW/cm2, expanding out onto an f/18 cone." What does the "expand out onto an f/18 cone" part mean? I thought that radiance is just in units of power/area/steradians. What does f-number have to do with anything?

Homework Statement The fundamental vibrational frequency of gaseous 14N16O is 1904 cm-1. a. Calculate the force constant, using the simple harmonic oscillator model Homework Equations K=u((2pi)(v))^2 u=reduced mass The Attempt at a Solution u=[(14)(16)/(30)] (1kg/6.02e^26)=...

Not quite sure if this is the correct place to post this, but I am having difficulty converting between AE and SI units. Having grown up using only SI units, the AE units are a little confusing. What is the conversion formula for degrees Fahrenheit to degrees Celsius incorporating a degree...

Homework Statement The half-life of an isotope of phosphorus is 14 days. If sample contains 2.9 × 10^16 decays such nuclei, determine its activity. Answer in units of Ci. Homework Equations / The Attempt at a Solution I know that one Ci is equal to 3.7*10^10 bq (or decay per second), I'm...

Homework Statement I need to convert a value in cm^3s^-1 to litres per second. I know that 1 litre=10^-3m^3 Homework Equations The Attempt at a Solution Could someone please help?

Having much difficulty with the problem below. Any direction would be greatly appreciated. A waste gas stream contains .045 mole of ammonia per mole of carrier gas. Its desired to design an absorber using water which will reduce the ammonia concentration in the exit gas from the absorber to a...

Homework Statement I have a lab report due next week and I'm almost done with it. However I'm totally stuck on the last part where it is wrote in a description of the experience : c=\frac{(m+M_e)(T_f'-T'_i)}{m(T_c-T_f)} where c is the specific heat of a metal. If I work out the units in the...

Homework Statement A Consistency question regarding the dimensions of the KG Equation. Homework Equations M^2=\frac{\hbar c}{G} for a quantization of gravitational charge on matter The Attempt at a Solution I know a few things however concerning the KG equation. It is directly...

Homework Statement The first equation below has units of voltage. Homework Equations V(t)=IR(1-e^{t/RC}) \rightarrow ln|IR - V(t)| = ln|IR|-t/RC The Attempt at a Solution the logarithm has units of voltage, but what does ln|IR| and ln|V| physically mean?

Dear Physics Gurus, o:) I am trying very hard to understanding the units used to measure torque. I know there is a unit called kilogram force centimeter, and 1 ounce force inch = 0.072007790632 kg force cm. My problem is I do not understand what these units mean. I could only find...

Geometrized units use the multiplication factor to convert for example mass to length, in this case the factor would is G/C^2. I know this is to do with setting c=G=1. How does one derive the multiplication factor from this? Any help greatly appreciated. Shane

Does the gravitomagnetic B-field (from the GEM equations) have units of frequency (1/s)? And if so, what exactly does the B field describe? I guess what I'm really trying to find out is whether the B field around say a rotating spherical object describes the rate of frame dragging, or does...

Homework Statement ok this might be a stupid question but I am working on a problem with springs and velocity and whatnot. anyways the units are american, 5lb, k=2lb/in, the diagram is dimensioned in inches. do i have to convert all them to N,kg,and meters. Homework Equations...

It really annoys me when professionals mess up unit conversions. From http://news.yahoo.com/s/afp/20090403/sc_afp/usclimatewarming_20090403144320 (1 million km^2 is actually 390,000 square miles.)

Homework Statement In a problem to determine the maximum elastic potential energy of a molecule, I have the following equation: A= \sqrt{\frac{6.626*10^-34 Js}{2\pi}}\times(\frac{1}{(1.14*10^-26kg)(1.85*10^3N/m})^(1/4) Homework Equations The Attempt at a Solution The answer is...

Hello! I was wondering if someone could help me with a problem of units! I'm currently deriving probability equations for neutrino oscillations and I'm stuck with units! I have: [(mass)^2 * time]/[4*energy] and I want to write it as [1.27 * (mass)^2 * distance]/[Energy] with distance in...

Im am trying to figureout how to calculate savings using a VFD - Variable Frequincy(Speed) Drive Direct energy savings easy I am trying to Calculate the savings in AIR FLOW/+/Air temp-differerance Not exausting 75'F air outside at say 10,000 CFM - And not bringing in 30'F Air in the...

This is perhaps a stupid question but: When we use natural units and set h=c=1, do we choose appropriate units so that their value is one but these constants still have dimensions, or are we somehow choosing h=c=1 to be a pure number with no dimensions?

Homework Statement Suppose that m = 1 mod b. What integer between 1 and m-1 is equal to b^(-1) mod m? The Attempt at a Solution m = 1 mod b means that: m = kb + 1 for some integer k Let x be the inverse of b mod m, note: x exists since b and m must be coprime due to the previous...

1. My teacher has given me a poster board to do on magnetic energy even though she has explained nothing about the subject, nor is there anything in my book. I am looking for the formula for finding magnetic energy and examples from everyday life. All I got was 1/2BH, but I have no idea what...

Homework Statement http://www.aijaa.com/img/b/00125/3627010.jpg http://www.aijaa.com/img/b/00758/3627011.jpg Homework Equations E_k=\frac{1}{2}mv^2 \vec{F}=m\frac{\vec{v}^2}{r} \vec{F}=q\vec{v} \times \vec{B} \frac{v}{r}=\frac{2\pi}{T}=\omega The Attempt at a Solution The...

How do you convert a length which has been given in MeV ^-1 to SI units? Energy is mass length^2/time^2 so I guess it;s easy to make the steps of energy - mass - momentum etc... What about length and time? Cheers

Dear PF members, In terms of natural units the reduced Planck's constant (\hbar) is 1 ML2T-1. Now in this terminology how a magnetic field can be expressed? thanks for your reply, rajini

When using the ideal gas law equation and solving for V, with constant R = 8.314 J·mol−1·K−1, what are the resultant units? L or m3? I always remember it being in L, but wouldn't it be m3 based purely on the units being put into the equation? Other units I'm using: P: Pa (not kPa) T: K

Hi all could anyone tell me what units are used in the equation E=MC. Thx, Dave.

Units -- is this m/s or mm/s? Homework Statement N/AHomework Equations Continuity A1*v1=A2*v2 A=pi*r² The Attempt at a Solution I've solved a problem as follows (pi * 10.0mm²)(0.200m/s)=(pi * 2.50mm²)(v2) 3.20 xx/s = v2 I am pretty sure it's in m/s, but having the radii in millimeters is...

Homework Statement Well, here's the homework question: A charge Q is located inside a rectangular box. The electric flux through each of the six surfaces of the box is: phi1=+1500Nm^2/C, phi2=+2200Nm^2/C, phi3=+4600Nm^2/C, phi4=-1800Nm^2/C, phi5=-3500Nm^2/C, and phi6=-3400Nm^2/C. What is...

I am solving the Hydrogen wavefunction using FORTRAN. Now using the Euler method, I am given a solution to match which is given by u10(r) = 1.06r*exp(-3.74r) (where unl(r) = rRnl(r) in general) which says it has a normalisation chosen to match what i should get from my code. Then I use the...

I am trying to make sure that the data I read off my multimeter has the right units. I have a multimeter that is a similar model to this one: http://www.tequipment.net/BK2703B.html You can enlarge the image to see the settings. When I measure AC current, my result says "2.95" when the...

I am reading something about thermodynamics and everything are not given in SI units. In the material, they use Fahrenheit for temperature, BTU for heat, lb for mass and in^2 for area. Now I need to calculate something with the data given in those units, well, I need to apply equation for ideal...

Homework Statement Let q be the number of units in finite ring R. Show that for all a in R, if a is a unit in R then a^q = 1. Is there a way to solve this without using group theory? All I can seem to find information on is when a and m are relatively prime then a^{\phi (m)} = 1 (mod \, m)...

The definition of matter is "anything that has mass and volume". Why doesn't the definition of matter mention anything about "time". Should time be mentioned as well since matter can't exist without it? Also, If matter had its own SI unit, what would it be? Edit:: a unit that could be...

Homework Statement Does Friction have units? Homework Equations U = Ff / Fn The Attempt at a Solution I know the coefficient which is "Mew" U, has no units whatsoever but I just wanted to know if friction itself had units.

Homework Statement rearrange to make p the subject then work out the units for p R - resistance or wire A - area in m2 l - length Homework Equations R=pl/A The Attempt at a Solution p = AR/l (m2 x m2kgS-3A-2)/m Resistance is ohms which is m2kgS-3A-2 I think...