What is Measurements: Definition and 394 Discussions

Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. The scope and application of measurement are dependent on the context and discipline. In natural sciences and engineering, measurements do not apply to nominal properties of objects or events, which is consistent with the guidelines of the International vocabulary of metrology published by the International Bureau of Weights and Measures. However, in other fields such as statistics as well as the social and behavioural sciences, measurements can have multiple levels, which would include nominal, ordinal, interval and ratio scales.Measurement is a cornerstone of trade, science, technology and quantitative research in many disciplines. Historically, many measurement systems existed for the varied fields of human existence to facilitate comparisons in these fields. Often these were achieved by local agreements between trading partners or collaborators. Since the 18th century, developments progressed towards unifying, widely accepted standards that resulted in the modern International System of Units (SI). This system reduces all physical measurements to a mathematical combination of seven base units. The science of measurement is pursued in the field of metrology.

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  1. U

    Entanglement – the order of measurements can be important

    Entanglement – the order of measurements can be important. I try now with some formulas - hope it's reasonably understandable: First known substance - unless I am floundering in it: I imagine that the p - photons is measured first (p1) and meets a PBS (0) (x = horizontal and y = vertical)...
  2. L

    How Can I Overcome Impedance Issues for Accurate Inrush Current Measurements?

    I'm trying to measure inrush current by looking at the voltage of a 0.1ohm resistor in the line within the first 50uS of flipping a relay to a variable AC source. Problem is that the new AC source that I have (chroma 61605) apparently has an impedance issue which prohibits good inrush...
  3. T

    Can measurements of red shift be affected by the shape of spacetime?

    I have read on some threads that there are other possible shapes for spacetime and I wondered could any of these spacetime shapes, or their change over time, affect our measurement of red shift? Also does the matter density at the location where a photon is emitted relative to our own...
  4. W

    Calculating error in measurements w/ uncertainty

    Homework Statement The radius of a circle is measured to be 2.4 cm +/- 0.1 cm. Find the error in the area of the circle. Find the error in the circumference. Homework Equations Have no idea but I'm taking a guess it could be multiplying fractional uncertainties? The Attempt at a...
  5. S

    Is My Three Phase Meter Giving Accurate Measurements?

    Hello all, Recently one of the power meters on one of our office's panelboards has been giving sensor garbage, calling the others' measurements into question. I have two 277/480Y transformers, one going to a two phase 480V duct heater and one going to the lighting (the meter reads three...
  6. A

    Searching for list of measurements of moon-earth distance.

    Can someone please help, I'm searching for daily (or weekly) list of measurements of moon-earth distance. Seems hard to find on the Internet. Regards, Jonathan
  7. H

    Accuracy of measurements from DAQ board

    Hello, I am confused as to how to determine the accuracy of a measurement of an AC signal from a Data Acquistion Board. I went to NI's website to look at the the specifications of the board I was using (a USB-6009) http://sine.ni.com/ds/app/doc/p/id/ds-218/lang/en#header0", and I don't know...
  8. G

    Energy Measurements of Particle in Superposition of States

    Given that E(n) = (n^2)E, and that our wave function PSI = 1/Sqrt(14)(Psi(1) + 2*Psi(2) + 3*Psi(3), what is the the value for the measurement of the energy? So, <H> = SUM((c(n)^2)*E(n)) where E(n) = (n^2)*E and c(1)=1/sqrt(14), c(2)=2/sqrt(14), c(3)=3/sqrt(14), which satisfies...
  9. Berlin

    Can the Universe's Dynamics Be Influenced by Quantum Measurement Frequency?

    I was tought that a physical measurement must be seen as an irreversible collapse of the wavefunction. I always thought that this is an ill defined statement. But let's assume that some macroscopic system is able to perform this act and that it is part of physical reality. My questions: has...
  10. W

    Subsequent Measurements of two observables, compatible and incompatible pairs

    Homework Statement On an arbitrary state, the observable \hat{A} is measured returning the result a. A compatible observable \hat{B} is then measured returning b. If \hat{A} is then measured again, is the same result a obtained? How about if \hat{A} and \hat{B} are not compatible...
  11. E

    Confusion over compatible measurements

    I'm still learning the formalism and structure of standard QM, so bear with me. My current confusion arises when considering the subsequent measurement of two commuting observables, for example the x-position and y-position observables of a single particle. Suppose the system is in a pure state...
  12. G

    Exploring Spin Measurements of Particles

    Homework Statement Say we want to fiddle with spin of a particle. The state in which a measurement of s_x is certain to yield +1/2 is: |+,x\rangle=\sin{\frac{\pi}{4}}e^{i 0}|-\rangle+\cos{\frac{\pi}{4}}e^{-i 0}|+\rangle=\frac{1}{\sqrt{2}}(|-\rangle+\+|+\rangle) Now, for this state, we want to...
  13. J

    Measurements corresponding to Exchange Operator

    The exchange operator P is hermitian--therefore it corresponds to some observable of the system. I've read on Wikipedia that this means "... we can, in principle, perform a measurement to find out if a state is symmetric or antisymmetric," but I have some doubts whether that is absolutely...
  14. S

    Evaluating Magnetic Field Measurements on a Cylinder

    Homework Statement In the figure the magnetic field in a region is vertical and was measured to have the values shown on the surface of a cylinder. Which of the following are true? http://www.webassign.net/mi3/22-111-CylinderB.jpg Which statements are true? 1. The measurements are...
  15. B

    Understanding RMS Accuracy for Measurements

    Hello, can someone please explain what exactly is meant when it is said that some measurement is accurate to some value RMS? Eg, "suppose that we have a bucketful of nominally 100-ohm resistors, accurate to 1 percent RMS" or, "we shall use an ohmmeter with an accuracy of 3 ohms RMS...
  16. E

    Nonlinear measurements - HUP violation or not?

    According to this article, researchers have obtained measurements with an accuracy larger than the upper bound set by HUP. http://physicsworld.com/cws/article/news/45535 My first thought is that this is not a violation, since we are talking about a finite number of measurements, but then...
  17. StevieTNZ

    Adroit Measurements in Reaching Conclusion

    Hi there, I came across http://arxiv.org/abs/arXiv:1001.1777" ('Addressing the clumsiness loophole in a Leggett-Garg test of macrorealism') where a solution to the loophole is adroit measurements. Before this paper (even version 1) was published http://arxiv.org/abs/quant-ph/0609079"...
  18. S

    In the reality how I perform the many kind of measurements, like operators p,q,E

    in the experimental side of QM, I know i can use a slit to measure the q. but what about p or E? and how to conciliate the measure with the theory?: after the measurement of a slit i'll measure q and the system will collapse in a autovector of q, like |q> but it will evolve like a...
  19. T

    Dark Energy Theory Gets Boost From New Measurements

    Dark Energy Cosmology makes the front page again: In a new study, a team of researchers led by Adam Riess of the Space Telescope Science Institute in Baltimore, report that they've calculated how fast the universe is expanding to a greater degree of accuracy than ever before, shrinking the...
  20. J

    Higgs mass from electroweak measurements

    I've seen the value 129^{+74}_{-49} GeV/c^2 mentioned in some discussion and wikipedia as a prediction of the higgs mass from electroweak measurements. Are the largest contributions to the error bars statistical in nature, and is is likely that the LHC can greatly increase precision of this...
  21. E

    Three question on error-propagation and flow measurements

    I’m calculating a discrete integral from distinct water-flow measurements. That means I have a few thousand data values in liter/second and I calculate from them the totally flown water in liter. The accuracy of the data is +/- 0.5 liter and I get one value every 5 seconds. The total time of...
  22. R

    Identifying a Radioactive Material Using Half-Life Measurements

    the assignment is written as follows: A parcel is attracting nervous attention at australian post. the parcel is radioactive and inspectors are trying to identify the material. Suppose they make the following measurements. There are 50 grams of the material and it's decaying at a rate of 0.25...
  23. G

    Book about Measurements in Astronomy and Cosmology

    Hello! I am a physicist. Although I think I understand quite well the laws of Newtonian physics and general relativity that explain the observable universe, I am a complete dummy in what concerns doing measurements in the universe. For instance, I have no idea how to measure the distance to a...
  24. T

    HIGH (800C+) wall temperature measurements - experimental help

    HIGH (800C+) wall temperature measurements - experimental help! Hi All - I'm seeking some advice from any experimentalist types. I'm working on a project analyzing heat transfer properties of exotic fluids. We have a simple experimental setup: laminar flow in a small diameter stainless steel...
  25. T

    Help me in selecting a power supply for conductivity measurements

    Hello all, For my project, I am trying to measure the solute concentration of water inside a porous ceramic plate (~2mm in diameter). I am using platinum electrodes. There are two ways I think I could possibly do this. 1) Place two electrodes on the sides of the porous disk 2) Place 4...
  26. Q

    Consecutive Measurements on One of an Entangled Pair

    I'd like some informed opinion on the following scenario, which in a certain article forms the basis of a controversial claim. Suppose an entangled spin anti-correlated pair of particles are generated by some process. Particle A flies off along the +z direction, particle B along the -z...
  27. H

    Interesting Optics Measurements?

    So I'm really interested in the field of wave optics, and luckily for my undergraduate program, we get to do a measurement project on any area of our choosing. I was looking up topics and there are some interesting ones such as the luminous fountain where they use the idea of fiber optics to...
  28. M

    Do all measurements need to be normalised?

    By way of a general inquiry, I was wondering whether all measurements in astrophysics need to be normalised for the effects of velocity and gravitation. By way of a broad generalisation of the relativistic effects being considered: Time Effects: o Time runs slower with reduced radius [r]...
  29. T

    Among the six measurements of the boiling point of a silsicon compound

    Question: Among the six measurements of the boiling point of a silsicon compound, the size of the error was 0.07, 0.03,0.14,0.08 and 0.03 degree C . Assuming that these data can be looked upon as a random sample from the population given by. f(x; \theta) = 2 (\theta - x) / \theta2 for 0 < x...
  30. M

    Uncertainty in measurements and epsilon delta definition of a limit

    does the epsilon delta definition of the limit connect to the uncertainty in measurements like this? like if we measure a quantity time with value a with error of + or - delta then my formula will give me v with value L +or - epsilon or is it unrelated?
  31. M

    What happens if two operators commute?

    I am trying to understand the idea of measurements on a system. Forgive me if any of my interpretations are incorrect...I'm hoping things can be cleared up. A measurement is taken on a system, represented by an operator, and this measurement changes the state of the system into a state...
  32. F

    Faster than 'c' measurements that do not violate relativity theory

    Homework Statement Some collections of stars called galaxies release jets of gas. Some of these jets have been measured to travel faster than the speed of light in a vacuum. Explain why relativity theory is not violated. Homework Equations This problem requires a qualitative response...
  33. F

    Anyone here worked on or know of near field antenna measurements?

    Hi, Im looking for some one who has worked on or knows the concept of near field antenna measurements. If there is anyone here I would really appreciate that you reply and answer some of my questions. I am having trouble with the sampling part for creating my plane wave spectrum.. I am...
  34. arivero

    Experimental measurements of decays into two photos that I have missed

    Is there some rumour about experimental measurements of decays into two photos that I have missed?
  35. pellman

    How do we associate real measurements with theoretical quantities?

    Let us take for granted for this discussion that we are clear by what we mean by macroscopic measurements: reading a number from a ruler, a scale, a gauge of any sort. Now suppose we perform a (macro) measurement of some aspect of a real laboratory system whose result, we presume, depends on...
  36. mrspeedybob

    Can measurements be made more precise then the measuring device?

    Suppose there is a quantity X to be measured. To do this you have a measuring device with a resolution of 1 and an accuracy of +/-1. It is imediately obvious that repeated measurements can yield an accuracy of +/- 0.5 but can any greater certainty be achieved? If 2 measurements are made and...
  37. W

    Is it possible to have a measurement with no uncertainty?

    Homework Statement If you were to measure ten identical measurements, would that imply that your measurement of the wavelength had no uncertainty? what would the uncertainty of the measurement be in that case? Homework Equations n/a The Attempt at a Solution I am thinking no...
  38. T

    Exploring a Negative Y-Intercept in Copper Resistance Measurements

    Homework Statement In our lab recently we measured the resistance of copper as a function of length. I plotted a graph with resistance as the dependent variable and length/area as the independent variable. I know the slope of the best fit line is equal to the resistivity of copper and that...
  39. P

    Understanding Charge Measurements

    Hi, Sorry if I have posted this in the wrong place. I'm having trouble understanding the difference between these four measurements of charge. Specifically whether the -/+ sign is important and what the unit is: For example, The charge of an electron is -1.602176487(40)×10^-19 coulombs...
  40. K

    Quick question regrading calculations and measurements in Science

    Would the approach taken to measurements and calculations be the same for the many different branches of science (Physics, Biology, Chemistry, and Earth science) that exist? Defend your answer by giving one example for reach branch of science listed. If someone could briefly answer this...
  41. C

    How Do You Convert Centimeters to Kilometers?

    I'm not understanding the steps when trying to convert. The question is... convert 43 cm to kilometers. centi-10^-2 kilo--10^3 Now, I'm not sure as to what steps I use in order to get the correct answer. If someone could explain to me how i'd really appreciate it. (: thanks.
  42. P

    What is the correct way to measure an electron's spin in a magnetic field?

    So I've gotten myself stumped the other day. Suppose I have an electron in a magnetic field, where the field is oriented along the x-axis, than I know that the H-matrix/operator is defined as -g*|B|*h/2 *Sx. Now say I know that I have a wave-function in a known initial state-vector, let's...
  43. D

    Finding the probability of energy measurements

    Homework Statement Hi... My problem says: In a given experiment the system, at the time t = 0, in the normalized state is given by: \phi(t =0) = \frac{1}{\sqrt{5}}(i\psi_{210} + 2\psi_{211}) What possible outcomes is possible if you do an energy measurement on the system in this...
  44. F

    Area under Gaussian peak by easy measurements

    First I try to find a way of finding area under Gaussian peak by using simple means. Questions at bottom of post. This concerns peaks with Gaussian distribution, eg. peaks in a chromatogram in some chemical analysis. The Gaussian distribution is f(x) = \frac{1}{\sigma...
  45. O

    Calculating Weight Loss Rate: TGA/DSC Measurements

    I want to calculate the rate of weight loss and not sure should I keep the initial mass at the initial time always or should I use the previous mass of recorded data should be m0 as inital value always or is should change to m3-m2, m4-m3, in this way. I plotted the graph and it does not have a...
  46. S

    Exploring Coherent States in LQG: Understanding the Measurement Process

    I’ve been starting to look at how LQG works, and if I’ve understood it correctly, just thinking about the kinematics, the quantum state of spacetime is encoded in a spin network. If I want to determine the volume of a region of spacetime, the result will be an eigenvalue of some volume...
  47. T

    Why Use Sense Resistors in 4-Wire Kelvin Measurements?

    In a 4-wire (kelvin) measuring system, why are there "sense" resistors? I understand that because there is very little current on the sense line there is no voltage drop. What purpose do they serve?
  48. e2m2a

    Are angle measurements rank 0 tensors?

    If I measure an angle in one reference frame to be 90 degrees, would it be 90 degrees with respect to all other reference frames? That is, is angle measurement a rank 0 tensor? I'm assuming all other reference systems are at non-relativistic velocities.
  49. D

    QM Measurements - probability, expectation value

    Homework Statement What are the possible results and their probabilities for a system with l=1 in the angular momentum state u = \frac{1}{\sqrt{2}}(1 1 0)? What is the expectation value? ((1 1 0) is a vertical matrix but I can't see how to format that) Homework Equations The...
  50. B

    Measuring Spin of Qubit: Analyzing Algebraic States

    I read in a book: For a qubit defined as: \frac{1}{\sqrt{2}}(|0\rangle + |1\rangle) Since |0\rangle and |1\rangle are the eigenstates of \sigma_z then measuring sigma_z will yield either |0\rangle or |1\rangle. Measuring \sigma_x on the same qubit will give one of the eigenstates of \sigma_x...
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