Measurement Definition and 1000 Threads

  1. Paul Colby

    Signal measurement ~50 pico volts

    Hi, my question may be too open ended in which case some help defining it would be helpful. The signal I wish to measure is estimated to be ~50 pico volts in amplitude generated in an HF AT-cut quartz crystal. Basically all the signal power will be at the fundamental mode resonant frequency...
  2. C

    B First Direct Measurement of Brown Dwarf Mass Limit: 6.7% Sun

    by Ken Croswell New observations indicate that objects born with a mass just 6.7 per cent that of the Sun can shine for trillions of years rather than fizzle out as failed stars known as brown dwarfs. Link: New Scientist
  3. R

    Selective Incident Headlight Intensity Measurement

    Hey guys, I am trying to come up with an idea to measure incident intensity of headlights from an oncoming car for one of my uni projects. This wasn't specifically assigned project topic, we get to choose what we want to do. It's my Instrument and Measurement unit, and I had this idea thought it...
  4. S

    I Possible to estimate the location of a measurement point?

    Hi guys, I am just wondering if it is possible to calculate/estimate the location of measurement point on a rigid body? For example, let's say we have a rigid body that is in motion. We attach a sensor, say an accelerometer on the surface of the rigid body. Now can we estimate the location of...
  5. E

    I General Questions Related to Quantum Measurement

    I've recently been wondering about the notion of measurement in quantum mechanics. While I'm aware that understanding and precisely defining the concept of a quantum mechanical measurement is at the heart of interpreting the subject, I would like some feedback on some aspects of this topic I...
  6. B

    Preparation of murexide indicator for Ca measurement

    I want to prepare murexide indicator for Ca measurement using EDTA titrimetric method. I am following the procedure set by the American Public Health Association (APHA), however, I only have murexide diluted with K2SO4 (1:250). I want to know if I can use this as a substitute, and if yes, how...
  7. S

    B Double slit experiment - doesn't measurement affect photons?

    All these videos and articles about the Double Slit Experiment say that if we "look" where the single photons go, they act like particles and if we don't "look" they act like waves, creating the interference pattern... BUT What does it mean to "look"? We're not using our eyes or any camera...
  8. Martin Pecha

    How van der Pauw measurement is influenced by the size of the sample

    Dear all, I am trying to use Van der Pauw method to measure some samples, however I cannot get where in calculations van der Pauw method includes size of the sample. F.e. if I have circle with diameter of 2 cm or 5 cm there must be a difference right? Can anyone explain to me why or why not...
  9. LarryS

    I Entanglement correlations vs. timelike measurement events?

    The experiments that have been done to demonstrate that entangled particles are correlated (or anti-correlated) have been designed so that Alice and Bob's measurement events are intentionally space-like separated. Thus demonstrating that the "ghostly action at a distance" is supraluminal or...
  10. Lafith

    Measure Entropy: Can Absolute Entropy be Zero?

    Can we measure 'absolute entropy' of a system. Also can entropy become zero at 0 kelvin.is it possible only theoretically?
  11. B

    Problem about measurement and probability of energy

    Homework Statement Homework Equations I solve the (a) , using even,odd function. So, C=1/a The Attempt at a Solution I don't know how to approach (b). I think that 'total energy of the system' doesn't mean expectation value, how can i get total energy and probability of them?
  12. C

    I Measurement precision question

    Supposing we have 2 circles in a 2 d space that can bounce off each other like balls. These circles are made of an infinite number of points. We put the centre of each circle on a line and send them towards each other along the line. Are they going to bounce off keeping their trajectory on the...
  13. S

    Is light speed limit an artifact of the math of measurement

    A delightful video here A lecturer derives special relativity in a world of bats and echo location using a bat (sound) clock. All communication is limited by the speed of sound. (so a parallel of our world and light speed communication) He ends up observing that in no cases for any observer...
  14. O

    B Basic question about double slit interferance

    I am new here so I will start with a warming up question :) My question is very trivial here we go: In double slit experiment when shooting one photon at a time, we get interference pattern. Then when we put a sensor at one of the slits the interference pattern disappears because we now know...
  15. R

    I Measuring Vectors: Defining Direction and Magnitude

    On wiki measurement is defined as: Measurement is the assignment of a number to a characteristic of an object or event, which can be compared with other objects or events. So a number. For scalars, I agree because they are described by a single number. But what about vectors? They have...
  16. G

    I Commuting observables vs. exchanging measurements

    Hi. I'm afraid I might just be discovering quite a big misunderstanding of mine concerning the meaning of the expectation value of a commutator for a given state. I somehow thought that if the expectation value of the commutator of two observables ##A, B## is zero for a given state...
  17. L

    I Measurement Science: True Magnitude, Error & Accuracy

    Hello. So one of the axioms of measurement science is that every measurement we make is an approximation and can never reflect the true magnitude of a physical phenomena. We would then go on to teach that there is a certain "true" magnitude which is something that experts or majority would...
  18. A

    Measurement of grinding wheel waviness

    I have done experiements on a grinding machine and have collected the data of grinding wheel profile (using a laser sensor). The raw data consists of info on grinding wheel profile, waviness and roughness (because of abrasive grains). I would like to process the colelcted raw data. I want to...
  19. F

    Measuring AC current with an oscilloscope.

    I have a technical question, for research purposes. I have LED that we probe in AC mode. To measure the applied voltage in AC and the light-response in AC is no problem. However I would like to measure the current going through the device as well and I would like to link it to an oscilloscope...
  20. N

    SR830 lock-in amp measurement problem

    Hello I am currently have difficulties trying to measure dc-modulated voltages while applying a dc current, via Sr830 Lock-in Amplifier (LIA). Basically, I apply an 2 GHz ac current (amplitude modulated@10kHz and referenced to the LIA for lock-in measurement) and a dc current to my DUT...
  21. M

    Finding thermal expansion problems for measurement technique

    I am trying to find examples problems on thermal expasions related to the subject of measurement technique Google but I can't find them.. I don't know exactly what could be asked but the problem will be related to: "expansion of measurement device" is given, and "expansion of measured...
  22. I

    Repeating measurement of observables?

    I have a question on my homework set and I'm not sure the principle behind it: 1. Alice measured an observable F (a matrix) and passed the measured system immediately to another experimentalist, Bob, who is going to measure another observable G. Alice claims that she can deduce the experiment...
  23. T

    What is a dynamic spectrum measurement?

    I was going through Figure S9 in this paper yet don't quite understand how one can assign a probability density to a dynamic spectrum measurement as the authors do. To my knowledge, a dynamic spectrum simply displays the intensity for each frequency channel against time as shown in Figure 1C of...
  24. A. Neumaier

    A Key problems in classical and quantum measurement

    Quantum mechanical foundations are usually phrased in terms of measurement. I believe this is the main cause why these foundations remain shaky after almost 100 years of a good mathematical basis. Classical mechanics never had any reference to measurement in its foundations, and hence it was...
  25. A

    Linear Regression with Measurement Errors

    Hello, I have a set of data, two columns, and each datum has its measurement error like illustration shows below: x | y --------------|----------------- x1+/-xe1 | y1+/-ye1 . | . . | ...
  26. R

    How do I convert cubic picometer to cubic centimeter?

    Part of the question says: An unit cell has a cell edge of 288 pm. I got to the part where volume (288 pm)^3 = (288 x 10^-10 cm)^3 I have no idea how that equals 2.39 x 10^-23 cm^3 Only the Bold part ^
  27. G

    B Height measurement on other planets

    If you measure the height of a mountain, you compare it's height with the sea level. But on let's say mars, how do you measure height when there is no sea to compare with? For example: Olympus Mons is considered to be the tallest mountain or vulcano in the solar system, but what is the level on...
  28. yecko

    Instrumentation vs Measurement: What’s the Difference?

    What is the difference between the noun "instrumentation" & "measurement"? Thank you.
  29. P

    Can Power Be Measured as V^2/R Using a Bench Meter?

    Hello all, I'm using peltier modules (also called thermoelectric modules) for a student project. If you're not familiar, they are small semiconductor devices that when heated on one side and cooled on another, power flows due to the Seebeck effect. I'd like to measure power coming from...
  30. N

    I Difference between measurement and passing through a gate

    My question is as follows, given a hermitian operator, what's the physical difference between performing a measurement on a particle to get an eigenvalue of said operator and acting on the state of the particle with said operator? What prompted my question is the swap gate used in quantum...
  31. henry wang

    What's the error in 1 repeated measurement?

    Homework Statement I have only repeated a measurement once, I cannot assume it is distributed as a Gaussian because there is so few data. How can I estimate its combined uncertainty? The Attempt at a Solution Total data: x1, x2 I calculated the individual uncertainties in x1 and x2 using error...
  32. A. Neumaier

    I Many measurements are not covered by Born's rule

    1. Within the framework of a Hilbert space for an atom one cannot find an observable in the sense of ''self-adjoint Hermitian operator'' that would describe the measurement of the frequency of a spectral line of the atom. For the latter is given by the differences of two eigenvalues of the...
  33. C

    Measurement standard for joules = Momentum in kilograms

    Basically, I found the energy of a photon using its frequency ((6.8*10^15) and E=(3.6496394*10^-16)) and so I then used "p=E/c" to find the momentum and got 1.2173887*10^-24 however I don't know the measurement of the momentum. Is there a better equation to use to find momentum, and what would...
  34. A

    I The Arrow of Time and the Reversibility of Decay Processes in Physics

    Hello! I'm an Engineer by profession with less knowledge of physics, so please be basic with me. After recently being intrigued by the double slit experiment, I started to read more and more about the same. At most of the places, it says that as soon a sensor is kept near one of the slit to find...
  35. pittsburghjoe

    I Explanation for the Quantum Measurement Problem?

    Do we yet have an explanation for the Measurement Problem that Einstein would have been satisfied with?
  36. A

    Apprentice in fiberoptics and test and measurement equipment

    I come from totally different field. studied previously business management but I was always fascinated by technologies. I find it really difficult to keep up with all the new terms and mathematical equations to follow up. I have to look after each words in every paragraphs. I have searched for...
  37. J

    B Measuring c from Earth: Is the Speed of Light Affected?

    I understand that c is the "ultimate speed" and that it is a result of the fundamental constant, the permeability of free space. But if this is a constant only to a "stationary" frame of reference, how can we accurately measure it from Earth? Since Earth is moving relative to a supposed "fixed"...
  38. quantumfunction

    B Do we measure the particle or the wavefunction?

    It seems to me that we don't measure a particle because a particle doesn't have an objective existence independent of the wave function or does it? The wave function in this case would have to be real because you can't have probability without the underlying possibility of a specific outcome...
  39. T

    Electrodes liquid contact electromagnetic flow meter?

    Hello, I'm interested in building a small non-invasive battery powered device that wraps around a pressured 1/2" pipe for measuring potable water. From https://en.wikipedia.org/wiki/Magnetic_flow_meter and watching youtube videos, it seems they all use electrodes which contact the liquid...
  40. F

    I Definition and measurement of proper length

    As I understand it, the proper length, ##L## of an object is equal to the length of the space-like interval between the two space-time points labelling its endpoints, i.e. (in terms of the corresponding differentials) $$dL=\sqrt{ds^{2}}$$ (using the "mostly plus" signature). Furthermore, this is...
  41. munirah

    How to differentiate GHZ state and W state?

    Good day, I try to differentiate GHZ-state and W-state using three tangle. Suppose The value three tangle for GHZ-state equal to 1 while W-state equal to 0. I used three tangle formula, $$\tau_{ABC}=\tau_{A(BC)}-\tau_{AB}-\tau_{AC}=2(\lambda^{AB}.\lambda^{AB}+\lambda^{AC}.\lambda^{AC})$$...
  42. AdrianMachin

    Measurement Uncertainty Problem in MIT OCW 8.01x

    Homework Statement What's the answer to (0.781±0.002)/(0.551±0.002)? Well, here is the answer (1.417±0.008) that professor Walter Lewin said in one of his videos. I checked this in an online uncertainty calculator and it turned out 1.417±0.006. Homework Equations n/a The Attempt at a...
  43. J

    Hydrogen Atom: Wavefunction collapse after measurement of Lz

    Homework Statement Suppose we have a wavefunction with n=4. If we measure the orbital angular momentum along the z-direction(no spin in this problem) and get 2*hbar then what are the possible values of the total angular momentum and what is the most general wavefunction after the measurement...
  44. V

    I Measuring Coordinates in Strong Gravity: Schwarzschild Metric

    We know that Schwarzschild metric describes an asymptotically flat spacetime. This means that far away from the event horizon we can safely interpret the ##r## coordinate as distance from the center. But when close enough to the event horizon the curvature becomes significant and our common...
  45. C

    Finding uncertainty of a measurement

    Homework Statement What is your average reaction time? What is the uncertainty? Homework Equations To find time I used the following equation: t=\sqrt{\frac{2(\frac{D}{100})}{9.81}} D is measured in cm, hence the division by 100 (to get meters). 9.81 is acceleration due to gravity (this comes...
  46. fsonnichsen

    Accurate measurement of pH - best methods

    I am "proofing" various pH probes in an in-situ fresh water environment--this is a low electrolyte environment where such probes typically do not perform very well. I want to routinely sample the water and obtain accurate pH data for comparison. Can someone enlighten me on the what modern (non...
  47. J

    B Why can't one metre be more than one metre?

    Hello, Recently, I have been trying to work on some philosophy that I am developing, and the subject of measurement has come up. My question goes a bit like this: Suppose that it turned out that when you measure point A to point B as exactly 100cm (one metre), there are actually three...
  48. Titan97

    B Position of a particle immediately after a measurement

    Say a particle was measured to be at a point C. Immediately after this, if i make another measurement, its given in griffith's book that the particle will still be found at C. Isn't this only possible if the particle was at rest?
  49. Q

    A Measurement of the Higgs Self Interaction

    Hello everyone. What measurements have been done of the Higgs self-interaction? If nothing has been done yet, what are the relevant groups and research articles describing the progress of work in this direction? If this has been done, I would love to know the references. Thanks!
  50. munirah

    How to calculate negativity measurement of quantum state?

    Good day, From my reading according to negativity for tripartite state, it is given as below; $$N_{ABC}(\rho)=(N_{A-BC}N_{B-AC}N_{C-AB})^{1/3}$$ with $$N_{I-JK}=-2\Sigma_i\sigma_i(\rho^{TI})$$ where $$\sigma_i(\rho^{TI})$$ being the negative eigenvalues of $$\rho^{TI}$$, the partial...
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