Questions tagged [measurements]

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1answer
113 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
95 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
77 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
83 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
17 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
114 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_{...
7
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1answer
222 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
734 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 ...
0
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1answer
479 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
433 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. ...
0
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2answers
61 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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0answers
297 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
111 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
93 views

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 ...
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1answer
129 views

If I cut a string, will its length be rational or irrational? [duplicate]

If I cut a string (lets say approximately halfway), will the length of each side (in inches) be rational or irrational?
74
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3answers
8k views

Can photons be detected without being absorbed?

I am thinking about a detector that would beep if light passes through it. Is it possible?
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2answers
121 views

Why do scientists do particle collision experiments more than once?

Why are the particle collision experiments involving the same particles are done more than once. Shouldn't the collision of the same particles with the same velocity as the experiment before give out ...
10
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3answers
653 views

Difference between measurement, state and system in quantum mechanics [duplicate]

This question refers to the following point made in Susskind's book Quantum Mechanics- The Theoretical Minimum: In the classical world, the relationship between the state of a system and the result ...
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1answer
88 views

Measuring through meter scale

What if the measuring thing is found to have length between 6mm and 7mm. Like u r measuring the length of an object which has the length between 5.6cm and 5.7 cm. The millimeter distance was between ...
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1answer
62 views

Formalism of non-communitive (quantum) probability space

In an old paper by Gudder http://www.ams.org/journals/proc/1969-021-02/S0002-9939-1969-0243793-1/S0002-9939-1969-0243793-1.pdf, he defined: "a quantum probability space is a triple $(\Omega, C, M)$ ...
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0answers
45 views

Continuous Measurement equations

In a physics text, "Quantum Measurement Theory and it's Applications" by Kurt Jacobs, it describes the idea of a "continuous measurement" (measurement taking place over time $T$): $$dy = x_{true}dt + \...
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1answer
98 views

Is there any situation where one can measure force WITHOUT motion?

I am drafting a patent application where one part of the invention measures a force. I'd like to distinguish this from the prior art, which measures a displacement. But for all the force measurement ...
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5answers
3k views

How do scientists determine when to disregard a model that has a higher correlation to data than another model?

For any set of data points, you can comprise a 100% correlated and fitted curve using a sum of sloped lines all multiplied by their respective Heaviside step functions to form a zig-zag shaped curve. ...
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3answers
2k views

Propagation of uncertainty in integral formula

I have a moving object with mass $M$ whose 1D trajectory $x$ can be tracked and known over time with a certain sampling rate (EDIT: to make it clear, I don't have the analytical form of $x$, that's a ...
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0answers
41 views

Ineffecient continuous measurements in quantum measurement theory

In a quantum measurement theory text "Quantum Measurement Theory and Applications" by K.Jacobs, he defines and explains the idea of a continuous measurement, which is a measurement $$y = x_{true} + \...
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1answer
274 views

Distinction between four non-orthogonal quantum states [closed]

Given an unknown qubit $|\psi\rangle$. It is promised to be in one of four possible states: $|0\rangle$, $|1\rangle$, $|+\rangle$ or $|-\rangle$, where $|+\rangle$ = $(|0\rangle$+ $|1\rangle)/\sqrt2$ ...
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0answers
31 views

Is it possible to obtain the richter grade of an earthquake with the data of an accelerometer?

I have an accelerometer on a table that gives me the $x$, $y$, and $z$ axis acceleration in $m/s^2$ when I move the table. Is there a formula or method to pass this data to a earthquake grade in a ...
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1answer
104 views

Projection on an axis

Can we say that the coordinates in 3-space corresponding to the Bloch sphere, by taking expectation values of the Pauli spin operators is the same as the projections onto the different axis? \begin{...
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2answers
2k views

Total and static pressure: which one is measured?

Which pressure is measure using measuring device in a pipe flow. My first intuition that it is the static pressure. This is confirmed by this Wikipedia article (link) The concepts of total ...
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1answer
47 views

Calculations involving quantum measurement operators

In a quantum measurement theory text, the following is stated. Please advise on the query regarding the calculation below. Consider the following measurement operator: $$\hat{A}(\alpha) = \bigg(\frac{...
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1answer
117 views

The physics of Harrison's marine chronometers

I have read some of the history of John Harrison's marine chronometers and have found it fascinating. I would like to deepen my understanding of Harrison's amazing inventions by learning more about ...
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2answers
45 views

Change in state upon localization of particle into a region (x, x+a )

Suppose I momentarily, with hundred percent certainty, assure that a particle is in range $(x,x+a)$, by using some sort of detector. If initial state was ket $\alpha$, what is the final state? Is ...
2
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1answer
100 views

How to construct a 12-micron thin layer of powder+epoxy?

Okay, this is more of an engineering tactic question perhaps, but any insight into any possible process will be very, very appreciated. So I'm mixing a powder with epoxy, making a pasty, fluid semi-...
0
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1answer
208 views

True white collimated light / nobody uses this?

Based on a previous question is this the difraction limit of our microscope? , I got the idea to use a true white parallel back light to illuminate an object for measurements (target accuracy is 1 ...
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1answer
418 views

How to estimate the frequency of the sample rate?

I'm studying for my class of physics laboratory and I need help with something: Let's say I need to deduce the constant of elasticity of a spring and I will do it using a dual-range force sensor, ...
4
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4answers
667 views

Definition of mass in Newtonian mechanics

I believe that for any physical quantity, to know what significance it has in any situation or that it's different from other quantities, we have to first start by assigning a value to it, or some ...
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1answer
56 views

Quantum Uncertainty in Measurement of Fundamental Quantities

Fundamental constants (such as electron rest mass or charge, which are stated with high precision and, I think, are believed to be certain), I believe are verified by measurements that involve some ...
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2answers
123 views

What happens if you make an observation of the spins of two entangled, far apart electrons at exactly the same time? [closed]

If we consider the spins of two, far apart, entangled electrons, what will happen if we make a measurement on both spins at exactly the same time (let's assume time is not discrete)? I see it as a ...
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1answer
129 views

understanding resolving power in QM

Consider the definition of resolving power of two states in quantum mechanics as being the absolute value of the difference between the probabilities of two states following the measurement averaged ...
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5answers
305 views

A non-metaphysical interpretation of measurement in quantum mechanics

In quantum mechanics, measurement plays a fundamental role and to me, its role is usually described in a rather odd way. The Copenhagen interpretation states thus When that device makes a ...
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2answers
44 views

Optimization problem and measurements

This is more of math problem, but my doubt is about the measurement units of the final answer so I figured I'd post it here. Problem: A lighthouse is located on a small island 3 km away from a ...
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1answer
202 views

If two commuting observables do not share eigenspaces, can't one measurement affect the other due to an extra wave function collapse?

When we learn quantum mechanics, we are told that the only way to extract information from a system is to conduct measurements. We are told that if two observables commute then performing one ...
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1answer
80 views

Is EMF/EMR additive (two devices produce twice the EMR)?

I'm interested in electromagnetic radiation radiated from home appliances. Wanted to know if I have two phones (for arguments sake assume that they are perfectly identical) and they both are in sync ...
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0answers
56 views

Measurement phrase: “determined to 1 cm precisely”, “centimeter-precision” [closed]

I'm not perfectly sure about the stated phrase (or similar ones since I had to translate it). Does it mean +-1 cm, or +-0.5 cm? I guess many people use it in the first way but only the latter will ...
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2answers
3k views

What are the problems with using spirit level experiment to prove the flat-earth theory?

Full disclosure: I do not believe the Earth is flat. However, a guy recently posted a YouTube video that purports to prove that the Earth is flat due to there having been no changes in the position ...
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3answers
4k views

How is temperature defined, and measured?

In questions like this one, temperatures of millions of degrees (Celsius, Kelvin, it doesn't really matter at that point) are mentioned. But, what does it mean exactly? What is measured, and how? As ...
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1answer
9k views

Dimensions of electric charge

I was studying dimensional analysis, which is a technique used in conversion of units, checking the homogeneity of equations and also sometimes deriving unknown equations, if we can guess the factors ...
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2answers
96 views

How do I measure loudness level of a device in environment?

I want to measure the individual loudness level of a device in environment. Fistly, I measure loudness level when the device is ON (95.5dB) Then I measure loudness level when the device is OFF (48....