Measurements Definition and 382 Threads

I am amused by how skillfully most of the texts I have avoid discussing reference electrodes in electro-chemical measurement-They simply start out by discussing the H2 and Calomel electrodes with no further explanation. Both have certain hazards and seem overly complicated. So--why are these...

[Mentors' note: Split off from this thread as it was a digression there] After you make a measurement and find the particle to be in a particular eigenstate, if you measure that particle again will you find it to be in that same eigenstate?

Homework Statement Consider an electron described initially by ##\psi = \frac{1}{\sqrt{10}} \begin{pmatrix} 1\\ 3 \end{pmatrix}##. A measurement of the spin component along a certain axis, described by an operator ##\hat{A}##, has the eigenvalues ##\pm \frac{\hbar}{2}## as possible outcomes (as...

I have a trivial question: when measuring 2 entangled particles A and B, what should be the timing between the measurments to get correct results? In other words after measuring A how long can we wait before measuring B before its state changes?

Imagine that we have an intertial system F, and there is an electric charge Q at the origin. Obviously the field is symmetric and spherical in this reference system. Imagine another inertial system F' that is moving at constant speed v to the right respect to F, and at t=t'=0 both origins...

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...

Homework Statement a) The equation governing the flow rate, , of a fluid under streamline conditions through a horizontal pipe of length l and radius r is: where p is the pressure difference across the pipe and ƞ is the viscosity of the fluid. Thus, a student conducted an...

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...

ok I know that anybody in the heavens will bend spacetime with the gravity it has. What I was wondering was how do we measure around them like from the Earth to mars. When Mars in now quit on the opposite side of the sun ( so we can see it at sunset). do we measure the parabolic curve in...

Why θ in radian equals arc/radius? I know that it can't be proved but there must be a explanation for this formula. How founder may have got this idea.

I am trying to read Hugh Everetts thesis about the universal wave function, which is now called the many worlds interpretation of QM. At page 53 ff. he discusses measurements. He talks about a system composed by two state functions, saying that the two subsystems can be considered as measuring...

Hello, I have an exercise here that I need help with. The precision in measurements of radial velocities by the Doppler effect is currently 1 m/s. Can a Jupiter like planet orbiting a star similar to the Sun at a distance from the mother star equal to the Sun-Jupiter distance be detected? (Use...

Hi. What's the exact relation between the assumptions "counterfactual definiteness" and "existence of free will"? I (think I) know their "definitions" in QM: counterfactual definiteness: ability to speak meaningfully of the definiteness of the results of measurements that have not been...

Homework Statement We have got two particles with S_1=1 and S_2=1. We know that S_{1z}|\psi_1\rangle=\hbar |\psi_1\rangle and S_{2x}|\psi_2\rangle = \hbar |\psi_2\rangle. a) Find wave function |\psi_1\rangle in S_{1z} basis and |\psi_2\rangle in S_{2z} basis. b) We measure S^2 of total...

How do we check consistency of measured data, e.g. x1 = 1 ± 0.1 x2 = 1.4 ± 0.3 I can do this for two different samples to check for significance in terms of different means, but how to check internal consistency of a single set. How can we do this using: a) standard normal probability table...

Homework Statement I am given some measurements and I am supposed to express them as standard SI units. I can't find any examples of this done online or extra practice exercises to help me. I am probably googling the wrong words. I have been out of school for quite a while and I don't know what...

Hello, I am using a Kalman filter with a PI controller. The goal is to control a mirror to stabilize the position of a laser spot: I am sending a disturbance on the mirror and the PI sends command to the same mirror so the spot stays fix. With a camera I am recording the image of the laser and...

If I have a cluster with a mass measured in M_500c, then how do I go about converting that mass to M_200c given some concentration and an NFW profile?

As a part of an experiment in radioactivity, we placed an alpha particles emitting source (Am) and a sensor in a vacuum chamber, and measured the power (number of particles per time unit) for various angles of the sensor. Our goal is to fit a theoretical function to our measurements (power vs...

I've been reading up on HMI, and the claims its proponents make are pretty impressive. I'm struggling to understand some details though, so I'm hoping someone here is more familiar with it. In http://www.vub.ac.be/CLEA/aerts/publications/1998Berlin.pdf, the authors describe a "macroscopic...

I'm looking through an old exam, and don't quite understand the solution given for one of the problems. We have given a wavefunction g(\phi,\theta) = \sqrt{\frac{3}{8\pi}}(-cos(\theta) + isin(\theta)sin(\phi)) and are asked what possible measurements can be made of the z-component of the...

Hi Me and a couple of class mates are working on our bachelor's project of which the mission is to measure the temperature of the sun using a parabolic antenna. We are having great troubles trying to come up with an equation relating the antenna temperature (which we are able to calculate with...

"A 2.4% Determination of the Local Value of the Hubble Constant" by Riess et al has led to some excited news stories recently. I don't see it discussed anywhere here. Looking for the essence of the paper, I note three things: The two measurements considered are "the Hubble constant ... measured...

Hello, guys! (And girls, but.. you know..) There are several things I do not quite understand, so, can you help me clear my doubts? ^^ 1) How do I know when to multiply the value of calculated data when it comes to determining the uncertainty of the data? 2) When do I multiply the percentage...

Hi all, I am reading about hall effect measurements and analysis from an old physics book, A. C. Melissinos, Experiments in Modern Physics, for a lab class I'm taking. An experiment involving hall and resistivity measurements of a p-type germanium sample is performed and discussed. He notes...

Hi. I am working on a linear algebra problem that arose somewhat like this: Suppose that you are shining a light with a known intensity spectrum P(\lambda) upon a surface with an unknown reflection spectrum, R(\lambda). You have a detector to detect the total reflected light intensity, I. How to...

I'm nearly at the end of my preliminary testing for a wind tunnel in my A2 physics coursework. My question for my project so far is: "Do different shaped objects exhibit different properties under the influence of high speed air". For my coursework I need to measure or observe something to get a...

Let me introduce notation so my question makes sense. A set of orthogonal states can be distinguished by a Q-measurement, e.g. |0> and |1> (Q-computation notation) can be distinguished by measuring with the observable Z which has eigenvectors |0> and |1> with eigenvalues +1 and -1. But if those...

Hi everyone, Is it normal if the acceleration measured is different with different instrumentation? I have measured the acceleration of shaker with three different accelerometer and I didn't obtain the same result. Thanks for your help!

I am just wondering if someone could tell me what 'a higher order QCD calculation relevant for exclusive measurements at the lhc' means? In particular, what is an exclusive measurement and are such QCD calculations done on the lattice or is it perturbative analysis? Is there something special...

Not long ago a very thoughtful thread cleared my mind on the Relativity of Simultaneity. I am very thankful and hope to get here help also on a question related to the RELATIVITY OF MEASUREMENTS in the moving reference frames. Suppose that innumerous bars (or rods) are loaded on a very long...

The other day, in conversation, I attributed the dictum, "If you can't measure it, it isn't real!" to Lord Kelvin. However, when I chanced to look it up in Wiki, I could find no confirmation of this attribution. Was I mistaken? Did Lord Kelvin ever say anything to this effect? If not, is...

Homework Statement We know: In a measurement of quantum mechanics (basic) the average value is the cosine of the angle between the orthonormal basis of the measurement apparatus and the qubit (vector) entering it. Question: How do we prove this?Homework EquationsThe Attempt at a Solution Can...

Homework Statement Suppose that two measurements are made on a qubit in rapid succession. The first is δz and the second is δn. Suppose the first results is always +1. Calculate the probabilities of obtaining the results +/- 1 for the second measurement in terms of the angle θ between z and n...

What is the point of new measurements of kg, by ##Si^{28}## ball and with Watt balance? Is it this a special moment because Avogadro numbers, ##N_A##, of both measurements agree? What values of ##N_A## were given by both measurements and what values of ##N_A## were before these measurements? I...

Hi :-) I'm working on my master thesis in the field of quantum theory; currently I investigante No-Go-Theorems like the No-Cloning, No-Deleting, No-Hiding, No-Communication-Theorems ans so on. There is a fundamental question which is somehow linked to the No-Communication-Theorem. Is it - in...

Homework Statement I place a water filled beaker on an electronic balance and zero the reading. Meaning the balance will not be measuring the weight of the water and the beaker. a.) If a ball is resting at the bottom of the beaker. What would the balance be measuring? b.) If I immersed and...

Hi all, I'm interested in high temperature sample holders of electrochemical measurements especially for Li-ion batteries. But I couldn't find one. Does anyone use it before? Best regards

Hello everyone I am trying to design a ramjet engine. For that I need measurements of its parts. Does anyone know how to calculate them or have a link to a website where I could find more information?

Is there an instrument or has there been an instrument that measures electron density in the ionosphere (50km - 450km)?

Hello, I would like to know if there are simple ways (using trigonometric functions) to calculate distances between an object and two cameras. I am using two CMUcam5 (pixy), closely placed (the distance between the two cameras is known). And I would like to calculate the distance between the...

I would say there is no way to predict experimental outcomes than mathematics. But "expressing physics" can be rather different. For example, how many times have we asked ourselves, "I see that the mathematics works out this way, but I want a physical explanation." Indeed, I have found that...

I was looking at the attached picture, where it gives the Higgs Mass obtained from the two different channels from ATLAS and CMS. Let's only talk about the diphoton channel : H\rightarrow \gamma \gamma From the ATLAS the mass value is: m_{Ah} =126.02 \pm 0.51 and the CMS: m_{Ch} =124.70 \pm...

Looking for typical experimental parameters for measuring emission spectrum of both H and H2, specifically gas pressures. Also would like to know typical pressure range where spectrum transitions from H2 to H. Thanks.

Does anyone here ascribe any particular broader meaning to them? Is that they represent indivisible units a consensus of sorts? Do they have real meaning or are they a kind of trite observation?

Hello again. In a double slit experiment with electrons, suppose that we have the instrumentation to measure how space-time is curved by these particles. Would it be possible to obtain the electron's position and momentum by measuring the change in the direction of photons that move nearby but...

I have got a sample size of 1000 and I calculated the mean probability of success of an event by breaking this sample size into sets of 50 and also have the standard deviation and standard error of mean of this success. Now I repeat this process and have another set of data. What will be the...

I have performed an impact test on different football shin guards to assess their performance. I am however confused with the readings measured by the accelerometer I have used. The sensor was attached to a striking mass of 4.3 kg which was dropped at different heights. The graph I have attached...

Hello, I'm trying to better understand entanglement in the context of measurements and interactions. (1.) Are uncertainty and entanglement linked together? Are the eigenstates of an observable entangled since a measurement of one of them collapses the wavefunction to a single eigenstate, making...

Hello I have been trying to find out how the data for the atomic mass of different isotopes is processed. I am vaguely familiar with mass spectrometry and other techniques used for the measurements and I know that the experimental results are coordinated by the Atomic Mass Data Centre. I am...