Questions tagged [measurements]

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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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128 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?
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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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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 ...
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3answers
620 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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84 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
61 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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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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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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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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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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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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265 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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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
103 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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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
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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
108 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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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 ...
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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-...
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180 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
408 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, ...
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647 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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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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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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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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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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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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195 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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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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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
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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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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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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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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....
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1answer
295 views

How to deal with outliers in experimental physics?

In experimental physics, is it generally considered a good practice to eliminate outliers? I was taught that, when doing a linear regression, I should prune all the data that doesn't fit within 3 ...
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1answer
98 views

Assumptions in the proofs for the optimality of Grover's Search Algorithm

I was trying to understand this paper in which it is proved that Grover's search algorithm is optimal. On page 4, beginning of section 2 of the paper the author says the following In the proof I ...
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86 views

Changing length of one second

This is not exactly a question about physics, but, I was wondering, what would be a clever new definition of second, which is currently defined as the duration of 9 192 631 770 periods of the ...
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377 views

Working principle of a DC clamp-meter

I am trying to understand how a DC clamp meter works and found this image: (Source: http://www.kew-ltd.co.jp/en/support/mame/detail.php?id=60) My first guess of how this works is that somehow Ampere'...
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1answer
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A quantum entanglement experiment

Suppose we have an entangled electron-positron pair, such that total spin is zero. Separate them, and let Alice measure the spin (along $z$) of the electron, obtaining, say, $+\frac{1}{2}$. All the ...
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Why do physical units have different prefixes than the ones used for counting? [closed]

For counting, we use thousand, million, billion, trillion etc. For physical quantities, thousand becomes Kilo, million is Mega and (short scale) billion is Giga. In both these systems, the consecutive ...
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Walter Lewin vids-why ± 0.5 cm uncertainty why not ± 0.1?

here is the link to walter lewin video lecture please jump to 13:13 https://www.youtube.com/watch?v=q9IWoQ199_o 8.01x - Lect 2 - 1D Kinematics - Speed, Velocity, Acceleration i thought that all ...
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1answer
442 views

Determine length of optical fiber [closed]

Say I have 1 km of the optical fiber on a reel. But I only need 200 m of it and I don't have a right optical source or say I don't want to lose time coupling the light into the fiber. I also don't ...
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1answer
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Pressure: Measurement vs Definition?

I'm a bit confused about the relation between how we measure pressure and how it is defined. Consider a gas inside a container, if we connect a manometer and read the height difference, we say that ...
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Question about extra zeros in measurement

I most often encounter data values in problems which have some meaningless looking zeros after the decimal point at the end. There is no non-zero number to the right of the zeros. For example, the ...
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How to get second-order equation from 2 first-order equations with the same dependent variable?

I have a current sensor thats returns an output in voltage (Ts) dependent on the current that passes throught the inputs (I) and the voltage feed input (Ta). I built a table and measured the Ts, while ...
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2k views

Significant Digits for different units [closed]

I read, From (iv), 12.3 has three significant figures. And from (v) we can infer that 12.30 has four significant figures. So let's say it's meters, then 12.30 m = 1230 cm = 12300 mm But 1230 and ...
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How to find the least count of Vernier Calipers when Vernier Scale Divisions are greater than Main Scale Divisions?

When Vernier Scale Divisions are smaller than Main Scale Divisions, the least count is given by $1 \text{MSD} - 1 \text{VSD}$. But what if say, $3 \text{VSD}=5 \text{MSD}$ ? Do we write the least ...
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455 views

Why does radiometric dating tell us the ages of rocks?

I understand well how radiometric dating works in theory. In practice, I'm not sure how one would calibrate this for rocks. I've always been told that we can determine rocks' formation time via ...
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10k views

How can a beam balance measure mass?

In Newtonian physics, mass is the amount of matter in an object. So, how can a beam balance measure the amount of matter in an object (which is the mass of the object).