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Questions tagged [measurements]

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The role of Lorentz transformation

I will assume that spacetime is flat four dimensional manifold equipped with a Lorentzian metric and define, Physical systems: any object that is capable of causing a response ( measurement) in the ...
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1answer
17 views

Uncertainty Decomposition in velocity signal

I have a timeseries with repeated measured velocity signal (almost periodic signal). To find the mean time-varying velocity, I have decomposed the signal and computed the ensemble-average and the RMSE ...
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SI redefinition of the kilogram - what is one measuring? [duplicate]

I have been reading about the new SI units and specifically, want to get a better understanding of the definition of a kilogram. It was written that the kilogram will be defined in terms of Planck's ...
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24 views

Units and measurement [closed]

least count of a stopwatch is 0.1 second .the time of 20 oscillation of a pendulum is found to be 20 seconds then percentage error in the time period is......? least count of a stopwatch is 0.1 second ...
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50 views

How does weak measurement affect quantum state?

I'm trying to understand how to describe the quantum state after weak measurement using these two toy examples. Hopefully, these simple examples and your answer will help others who want to learn ...
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31 views

How to measure a Bell inequality violation in IBM Q? (Or analytically)

I made some circuit to prepare a 2 qubit state, but I am having trouble understanding how to measure Bell's inequality. I know the inequality is of the form $$|E(a,b)-E(a,b')+E(a',b)+E(a',b')| \leq 2$...
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1answer
38 views

Question on finding the relative error

The question is as under: Find the relative error in Z if Z= A/B Z= A(B^-1) Relative error in A is ΔA/A and in B is ΔB/B My solutions are : As A and B are being ...
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1answer
32 views

What is the meaning of true value and uncertainty from a measurement?

I am taking the following example: Lengths of an object are measured as : 5cm , 5.2cm , 5.1cm , 5.5 cm. Calculate the true value and the error . The answer is True value = 5.2 cm error = 0.15 ...
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2answers
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Measuring the Thickness of a Paper

I'm supposed to come up with a way to measure the thickness of paper. I've come up with the following approach. Let us suppose we have a paper of thickness $?$, length $a$, breadth $b$, density $\rho$...
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2answers
55 views

Question on Time Interval [closed]

The question states The mean life of an elementary particle pion is $2×10^{-7}$ nanoseconds. The age of the universe is about $4×10{^9}$ years. Identify the time interval that is approximately half ...
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1answer
19 views

Calculating percentage error with significant figures

I have a problem with significant figures. In an assignment, the paper gives us data to $3$ significant figures to calculate some values but afterwards requires us to calculate the percentage ...
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16 views

Effect of variation in day length on timekeeping

I was reading about atomic clocks when I came to know that precise measurements of time have shown that the time for earth's rotation is slightly more that 24 hrs (on the order of 10^-3). I was ...
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0answers
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How to Measure Electric-Field Probe Sensitivity?

I am doing some reading on current methods for detecting electric fields. A figure of merit for the systems is, naturally, the minimum strength of field that can be measured, in units of Volts per ...
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1answer
37 views

What is the difference between resolution and least count of a measurement? [closed]

1.What is the difference between resolution and least count of a measurement? In my physics book the statement of a question is as under : " The time taken by a pendulum for 100 oscillations is ...
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0answers
21 views

Uncertanty in Chi-squared measurements, spectra-like

Let's say I have some observational data. For example: in a certain wavelength interval I measure the flux, 10 000 points, and I have the uncertainty for each one of them. For example: ...
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38 views

Can we describe the process of measurement in functional form?

The question was can we describe the process of measurement in functional form? We know hermitian operator can be used to represent measurement. In Heisenberg's picture, it even described the "motion"...
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1answer
29 views

Finding the range of time scales by dividing length scales by speed of light

My book states : The scope of physics is truly vast. At one end, it studies phenomena at the very small scale of length (10^-14 m or even less) involving electrons, protons, etc.; at the other ...
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30 views

Subtractive cancellation errors in the lab

I am quite familiar with the problem associated with loss of significance in numerical analysis. This problem seems to be an even bigger problem in the science lab, where subtracting one physical ...
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1answer
78 views

Is it true that in practice quantum fields are *always* measured by means of coupling to particle detectors?

I'm watching some lectures on Relativistic Quantum Information and in one of them - available here - the instructor is talking about measuring quantum fields. He then says basically that in real ...
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1answer
49 views

Why do many phones have very different specific absorption rate (SAR) values for head and body? [closed]

I'm deciding on which mobile phone to buy, and since we don't really know if electromagnetic radiation does or does not have adverse health effects (I'm considering cancer and fertility), I'd rather ...
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2answers
125 views

A theoretical limit of accuracy?

Is there an agreed upon/conjectured theoretical limit to our ability to resolve the accuracy of time?
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27 views

Would the voltmeters give different readings in a circuit with induced current?

$\def\vE{{\vec{E}}}$ $\def\vD{{\vec{D}}}$ $\def\vB{{\vec{B}}}$ $\def\vJ{{\vec{J}}}$ $\def\vr{{\vec{r}}}$ $\def\vA{{\vec{A}}}$ $\def\vH{{\vec{H}}}$ $\def\ddt{\frac{d}{dt}}$ $\def\rot{\operatorname{rot}}...
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1answer
36 views

Least count of Vernier

Is least count not always 1 main scale divsion-1vernier scale divsion or is it always least reading possible on main scale/ no of vernier divsions. question: 1 main scale reading be 1 mm Lets say 5 ...
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1answer
26 views

The difference in using a predetermined error or standard deviation for calculations

Please edit the thread's tags and content if there are mistakes. I am not sure where If I'm posting my question with the right tags. This is a simple question regarding the study of Linear Motion by ...
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56 views

Spacetime curvature and measurements

From a programming perspective, I've always thought of gravitational influence as a kind of vector field, (crudely drawn) which seems to attribute to the motions of bodies through the field ...
2
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1answer
73 views

Are there ways to detect/measure photons that don't involve electrons?

As per question, are there ways to detect photons, and/or to measure their energy, that don't involve any interaction with electrons? And if yes, are there detectors which use photon interactions with ...
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1answer
21 views

Convert negative parameters of Altitude Height into possitive using BMP180 Sensor

I am using BMP180 I2C sensor interface with Arduino and with the help of mentioned below code ...
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0answers
78 views

How do we quantify and measure the net entropy of today's universe?

We know that the Universe evolved from a very low entropy state in the early universe to very high entropy state of today's universe. What is the quantitative definition of the net entropy of the ...
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2answers
28 views

Would equipment that is wrongly used by a person be considered as a systematic error?

Would equipment that is wrongly used by a person be considered as a systematic error or a random or both? I would say a systematic error because a person could don't know how to use a ruler and starts ...
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2answers
107 views

Perfectly distinguishable states are mutually orthogonal

$\newcommand{\bra}[1]{\left<#1\right|}\newcommand{\ket}[1]{\left|#1\right>}\newcommand{\bk}[2]{\left<#1\middle|#2\right>}$ Let $H$ be a Hilbert space. We call states $\ket{\psi_1}, \...
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3answers
62 views

Uncertainty in ripetitive measurements

Good afternoon everyone, I have a question which is puzzling me and I did not found an acceptable answer yet. Suppose you have acquired some data from a measurement and you have the following numbers: ...
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3answers
137 views

Why is physics taught as if measurement doesn't affect the thing being measured? [closed]

I've recently started my journey in understanding the math of quantum mechanics and I've noticed a strange pattern. (I'm not saying that the popular interpretation of quantum physics is wrong or ...
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1answer
28 views

How to determine whether an alloy is single or multi phase

I would like to know what methods would be suitable to determine if an alloy of 2 elements is a single phase or two phase alloy.
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2answers
41 views

Is there experimental evidence for the irreversibility of the collapse of the state of a system due to a measurement?

It has been pointed out by one of my professors that, in quantum mechanics, the collapse of the state of the system by measurement is not time-reversible, i.e once the system collapses due to a ...
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1answer
47 views

When the barometer drops, my well level seems to rise - how?

I have a deep water well, with a length of 1/4" drip tubing, open at the bottom, taped to the pump 180' down. The other end of the tubing is connected to a gauge pressure sensor in the cabinet of my ...
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0answers
11 views

Calculating Uncertainty with Mean Absolute Deviation

I'm taking an Introductory Physics course and, when learning about approximating uncertainty, I was wondering if a more quantitative method would be to calculate the Mean Absolute Deviation using the ...
2
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1answer
65 views

Heisenberg uncertainty principle meaning and using it to determine approximate sizes confusion

I was always under the impression that the Heisenberg uncertainty principle tells us to what precision we can make a momentum measurement given a position one. However, when doing quantum mechanics ...
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1answer
136 views

Reflection Vector (Ray Tracing)

Snell's law of refraction at the interface between 2 isotropic media is given by the equation: \begin{align} \tag{1} n_1 \,\text{sin} \,\theta_1 = n_2 \, \text{sin}\,\theta_2 \end{align} $\qquad$ ...
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0answers
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Attempting to calculate the mobility from SCLC measurement (space charge limited current)

I performed an SCLC measurement on a p-type material (hole transport layer) for a solar cell. Referring to the wikipedia page:https://en.wikipedia.org/wiki/Space_charge The relationship between $J$ ...
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0answers
28 views

Can traps measure which path in an interferometer?

it is possible in an interferometer to block the paths with screens so that the particle is well located in one of the paths. I wonder if it is the same when instead of screen we use traps in which a ...
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1answer
85 views

Are there any physical quantities that are loglog?

Most units, e.g. for length, time, mass, etc, are linear in relation to the underlying property. But there are some special quantities, where the units can vary several orders of magnitude within the ...
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1answer
61 views

A delicate measurement?

The identity operation means that we are not disturbing the system at all. However, if we consider the following operation $$ \begin{pmatrix} 1 + \epsilon & 0\\ 0 & 1 + \...
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1answer
44 views

Experimental measurement of the radial excess

Update: I have updated the the question, see below. The radial excess due to the curvature of spacetime is a well-known prediction of General Relativity that is often mentioned in introductory texts, ...
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Porous nanostructure in TGA and DSC

How does the porosity in porous nanostructures, such as mesoporous silica, influence the observed response in Thermal Gravimetry Analysis (TGA) vs Differential scanning calorimetry (DSC) thermograms?
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1answer
57 views

Profile of a platinum-iridium meter bar

The former meter standard, platinum-iridium meter bar, had a specific cross section somewhat resembling mixed variant of letters "X" and "H" with serifs (Image source): What was the reasoning behind ...
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3answers
178 views

Shot noise in optics

There are many explanations to be found about shot noise in optics, but the answers I find are incompatible. There are three ways shot noise in optics is explained. (Note that according to ...
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2answers
81 views

Work definition does not make any sense for coherent states? TPM (two projective measurement) scheme

I'm talking about the relation that if we are in a isolated, quantum system that only allows for work exchange with the surrounding system we know from the first law of thermodynamics that $\Delta E = ...
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11 views

Can radio waves be detected using a coulomb torsion balance?

Radio waves are almost everywhere. shouldn't the coulomb torsion balance be sensitive to any passing through the device?
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1answer
147 views

How can a Lego version of a Kibble balance measure the Planck constant?

As the picture shows below [][1] in a Kibble balance, one can drop out the measurement uncertainty of $B$ (magnetic flux intensity) and $L$ (length of coil) by the use of two modes, force mode and ...
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1answer
62 views

Calculation of Thermometer Time Lag?

A couple of days ago, contributor 'Rogan Parks' posed the question below the page break. I was about to fully answer it when the OP for no apparent reason deleted his question. I find it an ...