Questions tagged [measurements]

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Quantum measuring simulation

Hi I want to understand a concept that I been thinking about. I'm trying to simulate the energy measurement of a system (a many body quantum system to be precise), and I'm trying to simulate a quantum ...
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3 votes
1 answer
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Error calculation for a relative difference with only one standard deviation (STD)

I have a quantity that is calculated with two measurements, but I only have a tabulated standard deviation for one of the measurements. How would I calculate the error on the calculated quantity? The ...
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1 answer
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What can I give as an example for a dumb instrumentation system? [closed]

I've searched through many websites and textbooks but none of them have given an example for a dumb instrumentation device.
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2 votes
1 answer
87 views

Is redshift an accurate method for measuring distances of distant galaxies and quasars?

I'm currently in 11th grade working on a science project about measuring distances using redshifts. I understand how the wavelength of a light wave increases when an object moves away from the point ...
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0 answers
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How to add markers to IR photographs

I'm using an IR camera to identify thermal patterns. The thermal images are similar to this [LINK] image. I'd like to add markers to the area being measured to determine dimensions and normalize the ...
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1 answer
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What is the cross-section area of an electrode when measuring electrolytic conductivity?

If we have two flat plates, then the area is understood easily. However, if our two electrodes are like this: then will we take the area of $S_1$ or $S_2$?
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1 answer
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Heisenberg microscope for momentum

In the "Heisenberg microscope", the position of a particle is measured using a photon. The higher the photon energy, the better the precision in measuring the particle location is, but the ...
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1 vote
2 answers
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Different fitmodels for different intervals

A number of points were measured and plotted on an XY graph. I want to have the best fit line for this graph. The best fit model for the first part of the graph is described by some function $f_{1}\...
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In Neumark's extension, can the PVMs be rank one projectors on the total enlarged space or does it have to be projectors on the ancillary space alone?

Starting with the definitions used. A PVM is a set $\mathcal{P} = \{P_i: P_i^2 = P_i, P_iP_j = \delta_{ij}P_j, \sum{P_i} = \mathbf{I}\}_{i,j=1}^n$, where $n\leq d$ on a Hilbert space $\mathcal{H}^d$ ...
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1 vote
1 answer
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How to quantify the uncertainty of the time series average?

Usually, we measure a fixed physical quantity, then we simply average MEAN on the measurement results and calculate the standard deviation STD, then the measurement result can be written as MEAN±STD. ...
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8 votes
1 answer
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How can an observer observe the metric of spacetime?

I don't mean how can we measure the metric in practice. I only mean in principle. Suppose you are an omnipresent being, no experimental limitations. What measurements do you need to measure the metric ...
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-5 votes
5 answers
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How can we define length unambiguously when measurement of length is dependent on perspective?

Suppose I have two unmarked rulers, both of same length in one perspective. Let me keep them at some place in the room , and I view them from another. In the other point of viewing, the perceived ...
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1 vote
0 answers
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Von Neumann measurement - the only reasonable way to describe a measurement?

Introductory thoughts: In many books on quantum mechanics, the Von Neumann measurement process (where the measurement device is modeled quantum mechanically) is described. For example by Schlosshauer (...
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I don't understand how Watt measured the volume of a mass of water vapor compared to that same mass in liquid phase

I don't understand how Watt measured the volume of a mass of water vapor compared to that same mass in liquid phase. In this text he describes the process by himself, but I can't understand it. Could ...
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How to measure water height thickness on infinitely flat surface with constant layer of water?

How would it be possible to measure layer of water on an infinitely flat surface, with every time different, but constant layer of water? I'm trying to measure thickness from $1\rm\,\mu m$ to $5\rm\, ...
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1 vote
2 answers
48 views

Hall sensor for electric(!) field?

Is it (in principle) possible to measure the strength of an electic(!) field with a hall sensor? I think so, for the following reasons: The hall sensor is a conductor. If we place an conductor in an ...
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3 votes
2 answers
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Can the SI kg be realized without superconducting josephson junctions?

This question is motivated by me trying to finish my answer to this question. In the 2019 SI redefinition the kg was redefined in terms of Planck's constant (and the second and meter): $$ 1 \text{ kg}=...
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1 answer
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Error propagation for the mean of time-series

From what I have read, when measure repeatedly the same quantity X N times and the measurements follow a normal distribution the uncertainty of the mean is $σ_{mean} = \frac{σ}{\sqrt{N}}$ where σ is ...
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17 votes
6 answers
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What does it mean that dimensionless physical constants cannot be calculated but only measured?

I have read a passage in Wikipedia about the List of unsolved problems in physics and dimensionless physical constants: Dimensionless physical constants: At the present time, the values of various ...
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2 answers
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How can we conduct experiments to verify formulas without special equipment? How was it done in the past?

If we wanted to verify experimentally/empirically as laymen without special instruments a formula such as $s=16t^2$ which is used to approximate the distance s, in feet, that an object falls freely ...
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4 answers
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In a least squares fit, is the resulting error in the fit parameters considered statistical/random error or systematic error?

In a least squares fit, if there is no error estimate on the input data points, is the resulting error in the fit parameters $\sigma_y$ (which is calculated from residuals) considered statistical/...
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1 vote
1 answer
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Uncertainty of output current in voltage-current converter

I have a problem comprehending some things about uncertainty in electrical measurements. Here is illustrative example from my textbook. We use voltage-current converter for measurement. U1 = 10V, I2 =...
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2 votes
0 answers
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Is there a "Moore's law" for humanity's ability to accurately measure fundamental physical constants?

The CODATA releases seem to represent the scientific consensus on what their values approximately are. Their accuracy improves over time. Say, for the electron mass, would it be accurate to expect a ...
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How does one measure an arbitrary observable $\Omega (X,P)$?

In classical mechanics, there exist experiments to measure any observable $\omega (x,p)$. This is because, once we measure $x$ and $p$ simultaneously, we can by extension say that we have also ...
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Uncertainty of frequency from tone generator app on phone

If I were to download a tone generation app (sonic) on my phone (Iphone 13) and use it to generate a sine-wave of a certain frequency, what would the uncertainty of the frequency be? How can it be ...
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3 answers
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What is the precision of number 4.03100?

Trailing 0s occurring after decimal are significant. Like 0.302000. Suppose I got the measurement reading of 4.03100, with clearly 6 significant digits.What's the precision of my measurement? Isn't it ...
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1 answer
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How exactly IS Newton’s second law verified experimentally?

In R. Shankar’s “Fundamentals of Physics : Vol 1” while discussing Newton’s Second Law of Motion, Prof. Shankar raises the question : how do we know Newton is right? I quote from the book : Take ...
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1 vote
3 answers
113 views

What is the 'complete' number system to measure objects we see in reality?

It is clear that we need at least the real numbers to measure lengths as it is very easy to construct a length of $\sqrt{2}$ geometrically. However, consider every physics situation where we want to ...
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0 votes
1 answer
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What is a proper resolution, and how many times of measurement needed for a credible experiments? [closed]

This question aims to understand a basic intuitive understanding and proper doing in practical situations for designing experiments. Resolution Suppose there is an object large as a hand. What is ...
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6 votes
2 answers
480 views

Why does plane mirror form image of same size as object?

Plane mirror form images of the same size as of the object. Also if we need to see ourselves completely in mirror, we would require a mirror of at least half out height. Assume I am 6 feet tall then ...
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Can a planet's rotational axis be determined with a Cavendish torsion beam?

Assuming an arbitrary planet with rotation was explored but for whatever reason (perhaps cloud cover?) the axis of rotation was unknown. Or they needed confirmation... the situation honestly does not ...
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1 vote
5 answers
143 views

Measuring the speed of an electromagnetic wave using an oscilloscope and a couple of wires

I've been trying to measure the speed of an electromagnetic wave with my oscilloscope. I used : a 2 CH + SG function oscilloscope (Hantek DSO 2D15), SG set on square wave signal, amplitude 5V, ...
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2 votes
1 answer
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Uncertainty of a PT100 temperature calibration

Description of the Problem: I have a PT100 that is calibrated by an external lab and used in our lab as a reference for calibrating thermocouples. In the end, I would like to have a complete ...
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3 votes
2 answers
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Determining the appropriate number of significant figures to report in least squares analyses

I'm tasked with fitting a set of data to a line using Excel's $\text{LINEST}$ least-squares fitting routine. The data are $l$ and $m$ values, assumed to follow the relationship: $$l = l_0 + {g\over k}...
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1 answer
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How can one measure the exact momentum of a particle in a quantum mechanical context?

According to quantum mechanics you can't measure both the position and momentum of a particle at the same time. A particle has an associated wave function. If you want to measure the momentum of a ...
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2 votes
2 answers
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Is Daredevil's superpower conceptually possible?

The Marvel superhero Daredevil is blind but has heightened senses, enabling him to perceive the world around him to a far greater extent than a regular person. In his depiction in the Netflix live-...
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11 votes
2 answers
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If a measurement has 5% error, can we say it has 95% accuracy?

Most often when, in a numerical problem, it is demanded that we calculate the accuracy of the final result, we write the final result in terms of the error. So I want to know if, in a measurement, ...
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0 answers
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What materials will work for a Millimeter Wave Dosimeter?

Hi I'm trying to duplicate the experiment in this paper. However, I'm having some trouble sourcing the carbon loaded teflon described in it. What other materials would work? Specifically, would ...
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1 vote
3 answers
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Validity of power law fit (and analytical fit choice)

Context I am carrying out molecular dynamics simulations of trapped ions in a radio-frequency field of amplitude $U_{RF}$ + DC (see details https://arxiv.org/abs/2102.04098). I am studying radio-...
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3 votes
0 answers
72 views

Can experiments show if there are real non-local hidden variables?

Local hidden variables are ruled out by experiment (Bell). Non-local ones are not excluded though. Are there experiments thinkable to discern if they really exist or if reality is intrinsically ...
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1 answer
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Significant number and Measurement resolution

It would be kind if anybody could explain how many significant numbers do we have in 0.00034 if the resolution is 0.001? Without the special mention of "the resolution" my answer was 2, But ...
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0 votes
1 answer
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Minimum information required to measure your local physical environment

In Andy Weir's "Project Hail Mary" protagonist Ryland Grace wakes up in an environment and with a few physics experiments timing falling objects he relatively quickly determines that he is ...
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0 votes
2 answers
43 views

Is there concurrency or is it just missing precision?

Imagine I measure the time of two balls hitting the ground. My stopwatch displays 5.5 seconds for both of them. Then I could say, that both balls hit the ground at the same time. But if I add a few ...
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0 votes
4 answers
81 views

Some books write coulomb force is medium independent and some write it is medium dependent why so?

Some authors say coulomb force is medium independent others say it is medium dependent. I know value of universal gravitational constant does not depend on medium.But value of permittivity does depend ...
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2 answers
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Are there any effects upon a proton an electron can impart when returning to its ground state after absorbing and emitting a photon?

Basically the title. When an electron and proton are bound say within a hydrogen atom, are there any measurable effects upon the proton when its electron goes through the process of absorbing, ...
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3 votes
3 answers
120 views

Can we measure the ground state energy?

If we consider a quantum harmonic oscillator, the ground state energy $\hbar\omega/2$ is typically stated to be not measurable, as energies are always measured as relative values (energy differences). ...
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Is there data for natural background radiation measurement?

I am looking for raw data of alpha/beta/gamma particles natural background long-term measurement (preferably day by day or second by second for at least a few weeks), but cannot find any. I would be ...
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2 votes
1 answer
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Why does everyone keep using torsion balances for measuring the gravitational constant?

Most of the experiments aimed at measuring the gravitational constant use very complex setups involving suspended balls (Cavendish-like experiments). This is however not exactly the ideal setup – and ...
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Calibration of a Pfizer type hardness tester

I am working on testing of hardness of pellets for their hardness and crushing strength. Currently I have a Pfizer type harness tester at my disposal. It came with a default spring, which we found was ...
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1 vote
0 answers
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Linear response theory, but with measurement issue

In the standard linear response theory, the variation of an observable $A$ at time $t$ due to the perturbing Hamiltonian $H'$ is $$\langle \delta A(t) \rangle = \int_{-\infty}^t dt' \langle [A(t), H'(...
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