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Questions tagged [measurements]

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1answer
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Measure mass of an object only using gravitational force

Most if not all of our everyday methods of determining mass / weight work on the principle of normal force. The push provided to you by the surface which allows to sit/stand/lie down over it.The ...
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2answers
75 views

Problem of measuring barrier potential by a voltmeter

I have read in my book that The barrier potential of a diode junction cannot be measured by a voltmeter only. It says that the thermal equilibrium is disrupted. Besides , the contact potential is also ...
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5answers
865 views

What do clocks measure?

I recently asked a question about the measurement of time, and it has become apparent that I'm really asking a set of related questions, the premises of which need to be shored up and articulated ...
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1answer
17 views

Error regions in a simplistic measurement

Suppose I measure two certain parameters, $a$ and $b$, in an object $O$ for two instances. My measurements are Instance 1----> $a=1.4$, $b=1.4$ Instance 2---->$a=1.5$, $b=1.4$ Can, I say, hence for ...
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1answer
69 views

Probability of obtaining general quantum measurement outcome

The Fundamental Theorem of Quantum Measurement is stated as follows: Every set of operators $\{ A_n \}$ $n =1,...,N$ that satisfies $\sum_n A_n^{\dagger}A_n = I$ describes a possible measurement on a ...
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1answer
52 views

Three levels system and measurement

A three levels system has the hamiltonian $$\mathcal{H}=\begin{pmatrix}E_0+\alpha&&\\&E_0&i\beta\\&-i\beta&E_0\end{pmatrix},$$ with $\alpha,\beta\in\mathbb{R}$, $\alpha>\...
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0answers
51 views

Estimate the body surface area [duplicate]

This is a question back when I was in the third year of my (junior) middle school. However I still do not know an elegant answer to it. The question is composed of a single line. Measure the body ...
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1answer
229 views

Are ‘fundamental measures’ a thing?

The question I want to ask is: What measures are needed to describe the physical world and what are the fundamental ones of those, in the proper sense of the word fundamental? But that might be too ...
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0answers
37 views

Is there a formal definition of what a significant figure really is? [duplicate]

What does it mean, formally, when we say that a digit in a number is a significant figure?
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1answer
35 views

How do uncertainties in digital measurements work?

Suppose I stand on an electronic weighing scale, and it reports my weight as 74.5 kilos. Usually a lot of books would say that the last digit is uncertain, and that the uncertainty is 0.1kg, and that ...
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1answer
96 views

Does the symbol $K$ mean anything besides kelvin in any context of this scientific paper on the second page on the chart? [closed]

I was looking at this scientific paper(https://arxiv.org/abs/1205.1684) and I saw them use the symbol "K" for a nemerical value, but due to the context of the paper I wasn't sure if they were talking ...
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1answer
234 views

How to measure a static electric field?

I looked up google but didn't find any design for measuring electric field that doesn't vary with time. My own idea is to use two parallel plates (like a capacitor but without the dielectric). In an ...
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1answer
59 views

How is the energy of a particle measured in a Cherenkov detector [closed]

I don't understand how is the energy measured in a cherenkov detector. How is the number of photons radiated related to the energy of the particle or the measure of energy has nothing to do with the ...
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1answer
48 views

When does a particle in a quantum state interact with matter?

Lets have a particle in vacuum. If we do not observe, the Quantum Theory & Copenhagen interpretation says that the particle is nowhere and at the same time it is somewhere ( i.e the quantum state $...
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1answer
197 views

What is a destructive measurement?

What are destructive measurements or incomplete measurements, and what is the (conceptual) difference between them and a usual measurement? I read somewhere that destructive measurements consume ...
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1answer
79 views

Toy model for entangling interaction?

Most of the time entanglement is described using some instantaneous classical measurement from an apparatus, but it is possible to describe it between two quantum systems, with two systems $O$ (for ...
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1answer
71 views

How can energy in Ev of particles e.g. muons be measured in a cloud chamber?

I have a Wilson thermoelectric cloud chamber and would like to obtaine the energy of cosmic particles e.g. muons. I would greatly appreciate your answer.
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1answer
196 views

Maximum Uncertainty of a Measurement?

I know the state of a system at a time T1, and perform a measurement at a later time T2. My question is this: is there a maximum uncertainty on what state I could expect to measure the system? Of ...
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1answer
115 views

Quantum measurements

I am reading the paper "Unconditionaly verifiable blind computation". It says at p.9: a measurement in the $\lbrace \vert +_{\phi_i^{\prime}}\rangle, \vert -_{\phi_i^{\prime}} \rangle\rbrace $ ...
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4answers
739 views

Determining the value of Pi empirically [closed]

A shower thought hit me so hard I had to come here and ask: Outside pure mathematics, where should I look, if I wanted to physically measure the best possible approximation for $\pi$? How many ...
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1answer
47 views

What type of time dependent measurement would be the same whole over the world?

What type of periodic measurement would be the same all over the world at the same time? What I mean is there a phenomena that is observed similarly all over the world at the same moment. A ...
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0answers
41 views

Measurement of the $(|x_0\rangle + |x_1\rangle)$ state

We know that, in a quantum-mechanical system, for every pure state, there always exists a measurement whose outcome is known. How would you physically describe a a position measurement of the state $(|...
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1answer
288 views

Acoustic power spectrum of a natural turbulent flow

For a long time I've been curious about predicting the acoustic power spectrum of river sound from hydrodynamic measurements. What got me started thinking about this topic was repeatedly observing ...
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1answer
69 views

Quantum measurement operators defined with Poisson distribution

I have defined a set of quantum measurement operators of the form $$A_C = \sum _M \sqrt{Pr(M|C)} |M \rangle \langle M|$$ where $Pr(M|C)$ is the Poisson distribution $$Pr(M|C) = \frac{e^{-C}C^M}{M!}~~~~...
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2answers
312 views

How to measure mass of a Mosquito?

I though of a solution, by taking large number of mosquito and then measuring their mass and then averaging over, to get mass of a single mosquito. Is there anything other way than this?
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4answers
4k views

What is the quantum mechanical definition of a measurement?

I hear the word "measurement" thrown around a lot in quantum mechanics, and I have yet to hear a scientific definition that makes sense. How do we define it?
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1answer
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What is currently the approximate precision or accuracy $\delta r$ with which the position $r$ of an electron can be measured?

The measurement of the position of an electron has associated, on the one hand, a quantum uncertainty $\Delta r$ which gives an idea of the probability cloud where the electron can appear, for example ...
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0answers
34 views

Measurement of a single qubit in a composed system

Let $|\psi\rangle = |\psi_1\rangle \otimes ... \otimes |\psi_n\rangle$, where $n \in \mathbb{N}, n\geq2$ and $|\psi_i\rangle \in \mathbb{C}^2$ is a quantum state, for all $i \in \{1,...,n\}$. Let $i ...
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0answers
55 views

Altering the wave function without detecting the particle

Let's say there is a particle confined in a box, and therefore there's a wave function which we can use to determine the probability of the particle's state. Next, a measurement is performed which ...
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0answers
21 views

What is a revolution frequency spectrum?

I would like to know what is a revolution frequency spectrum? I stumbled over this in the context of detector physics respectively with resepect to the measurement of the beam (beam revolution ...
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1answer
83 views

What is the uncertainty of a given measurement?

When we are in the lab, I know how to get the uncertainty for a measurement I make directly or indirectly, but what would be the uncertainty in measurements that are directly given to us? For instance,...
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0answers
92 views

Measuring Entangled State in Other Bases

How does one determine the possible outcomes of a set of successive measurements in the bases $Y_a$, $X_b$, $Y_c$ for a set of entangled states, for example of the form: $$\psi = \frac{1}{\sqrt{2}}(|...
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0answers
35 views

Why the reference for kilogram has to be round in the Avogadro Project? [duplicate]

The question popped into my mind after reading this post and the corresponding Wikipedia article. From what I've understood (please correct me if I'm wrong), they wanted to redefine the Kilogram. So ...
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1answer
50 views

Error propagation and averaging

How is a value for x reported in the following example: x=by b has some error Δb and is constant, y is a measurable quantity with some error Δy In the case that 5 measurements were taken for y (all ...
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1answer
111 views

How to measure radius of the Earth in cloudy weather?

The two methods I know to measure Earth's radius — the method of Eratosthenes and the stopwatch method — require the Sun visible during measurement. But in my location such weather is quite rare: it's ...
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2answers
94 views

Is the choice of the automorphism of complex numbers relevant for Quantum Computing?

In Yale's paper, automorphisms on complex numbers $\mathcal{C}$ are shown to be wild, allegedly with cardinality $2^{\mathfrak{C}^{\mathfrak{C}}}$. There are two well-known ("trivial") automorphisms: ...
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2answers
71 views

Can observation affect the probability distribution of an event to occur?

It's already well know that in quantum mechanics the act of observation affects the outcome of an experiment making the wave function to collapse.Now in order to clear up my confusion about this topic ...
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1answer
80 views

Why do we call (the measurements we take in physics) approximations?

If a caliper takes the measurement to the 2 decimal points then is it not a correct measure to the 2 decimal points or is it still an approximation?
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1answer
16 views

How to Level Measure a fluid from under/inside/below the liquid? | Level Measurement Instruments

Level Measurement in liquids. I'm aware of all direct & indirect methods of measurement in Level Measurement. However, what are some methods that enable us to measure fluids from inside, or below ...
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2answers
109 views

Probability of Obtaining a Certain Value (normal distribution)

In my textbook it says that the probability of obtaining a value (which its Gauss distribution is known) is simply ($\frac{1}{\sqrt{2\pi }}$ * $e^{\frac{(x_{1}-X)^{2}}{2\sigma ^{2}}}$ dx ) where $x_{...
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1answer
215 views

Can a measurement partially “collapse” a wavefunction?

Let's say I have a wavefunction $\Psi$ which can be decomposed into a sum of it's energy eigenstates: $$ \Psi = a|1\rangle + b|3\rangle + c|8\rangle + d|10\rangle$$ Where, of course, $|a|^2 + |b|^2 +...
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0answers
706 views

How does diameter of manometer affect the sensitivity of the manometer?

I have a physics question on How the sensitivity of the manometer will change if a narrower tube is used for the manometer. Logically speaking, it seems normal for the sensitivity of the manometer ...
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1answer
458 views

Standard deviation as uncertainty of a single measurement

If we have made the following several measurements of the quantity x that follow a normal distribution: 86, 85, 84, 89, 85, 89, 87, 85, 82, 85 The mean is 85.7 and the standard deviation(std) is ...
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4answers
403 views

How many significant figures should one give in stating an experimental uncertainty? [duplicate]

How many significant figures should one give in stating a experimental uncertainty? For this purpose I found three rules: Experimental uncertainties should be always stated to 1 significant figure. ...
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2answers
60 views

How should a hydrometer be read?

Probably due to surface tension the surface tends to curve near the hydrometer forming a meniscus. The question is whether it's correct to read the hydrometer at top of the meniscus or at the liquid ...
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1answer
27 views

Incorporate uncertainty of position to my result

The data is a list of measurements of power $P_i$ with estimated uncertainty $\Delta P_i$ and another list with measurements of positions $x_i$ and estimated uncertainties $\Delta x_i$. All the $\...
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289 views

Experiments are monads (I think), but are they comonads too?

Quantum theory is equally an epistemic (ie about information) and ontic theory (see "reality of the wavefunction" on Google Scholar). My question is about a theory that aligns with this, ie, the ...
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1answer
104 views

Question when comparing two experimental results

In my textbook it says that if two experimental results vary less than 3$\sigma$ then they can be considered to have arrived at the same result. My question is how do you determine this "x$\sigma$". ...
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1answer
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Quantum measurement through entanglement

Lets assume I have a particle A which I want to measure it's spin. Based on what I have read about entanglement and measurement we can entangle a particle B with A so that B somehow registers(measures)...
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1answer
40 views

How can the color of the sun be measured?

As the sun sets it changes color, sometimes first becoming orange, then red, for example. The device typically used to measure color is a colorimeter, but all of the colorimeters I have seen only ...