The result of sampling the property of a system

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2answers
42 views

Why doesn't precessing a spin cause a measurement?

When an electron is placed in a magnetic field, its spin precesses. Why doesn't this reveal the spin via angular momentum being transferred into the environment? Impractical Thought Experiment ...
0
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1answer
39 views

Difference between 1 unit of a physical quantity and the unit of that physical quanity and how is the unit of derived quanities obtained? [on hold]

Is there any difference between the unit and 1 units of a physical quantity and how do we define the unit of a derived quantity. For example,the SI unit of length is m and 1 unit of length is 1m.Are ...
0
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0answers
12 views

How to calculate counting rate of two detectors in quantum eraser experiment?

How to calculate the counting rate between two detectors? In their paper this one , they use Glauber Formula. But I don't know this formula and can't find this formula online.
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0answers
7 views

How can I measure radiance?

I'd like to measure radiance in order to see how accurate the Lambertian, Phong models are and maybe to measure the "shininess constant" of a material (which appears in the Phong Model) on some ...
3
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4answers
501 views

What truly is mass, and is there a direct way to measure it?

We know a mass of an object of one kilogram as an object that weighs W = mg = 9.8 N and we reference it to that, (when it should as a fundamental parameter describe weight not the opposite). But if we ...
13
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2answers
935 views

How precise can current technologies measure the mass of an object?

Masses of various objects are listed on this wikipedia page: Orders of magnitude (mass). For example, mass of an HIV-1 virus is on the order of 1 femtogram. Are these data actually measured (which I ...
2
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1answer
23 views

Correction for uncertainty of multiplications and divisions

The conventional means of obtaining uncertainty of $c$ where $c = a \cdot b$ is adding percentage uncertainty of $a$ and $b$. This method seems to have a flaw as shown below (please excuse me if I am ...
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0answers
25 views

Why does't the use of the same number of significant digits result in consistent result?

Here is a table: $ \begin{array}{ c c c c c c c } Trial number & Time for 20 cycles & Period & Frequency & Wavelength & Velocity (wavelength*frequency) & Velocity ...
1
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2answers
660 views

Is it possible to use induction ampermeter to measure power consumption of electric water heater and dryer?

I hope this practical question is not OT and not too trivial for this forum. I am renting an apartment in a duplex with a shared water heater and dryer. Turns out, both water heater and the dryer are ...
3
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1answer
73 views

Measuring very long half lives accurately

There are already some questions about long half life times for radioactive elements, explaining how to calculate the half life time. Now I am wondering: When you have some radioactive material and ...
0
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1answer
53 views

Measurement on two Qubits

Assuming I have two Qubits, i.e. a four-dim. Hilbert space. In the following, I choose the basis {|11>,|10>,|01>,|00>}. I want to have a look on the non-diagonal part <11|$\rho$|00>. How can I ...
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1answer
221 views

Thought Experiment: Force on magnets in a Stern Gerlach Experiment

Background: In the SG experiment, an inhomogenous magnetic field affects a force on particles passing between two magnets. "Measurement" takes place when a screen is placed on one end, blocking one ...
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0answers
14 views

Total uncertainty of multiple stereo camera depth measurements

I have a stereo camera that measures depth for a rectangular area of pixels in a single image. Each depth measurement is obtained independently (this goes back to the stereo matching algorithm used). ...
3
votes
0answers
40 views

Calculating statistical significance of peak over background in counting experiment

I histogrammed the invariant masses of particular events in a counting experiment. There is a specific peak which towers over the expected exponential background. How can I give the statistical ...
0
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0answers
11 views

Rarefaction/compression events detection using time resolved sound measurement

I had a question about sound measurement in air using a B&K condenser microphone. In the acquired time resolved sound measurement signal I can see both negative and positive voltages/ pressure ...
4
votes
4answers
208 views

How does one describe a state with a density matrix after measuring position?

My question is about position measurement in non relativistic quantum mechanics. I've been taught that when you measure the value of an observable for some state of a system described by ...
7
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7answers
719 views

Shouldn't the Uncertainty Principle be intuitively obvious, at least when talking about the position and momentum of an object?

Please forgive me if I'm wrong, as I have no formal physics training (apart from some in high school and personal reading), but there's something about Heisenberg's Uncertainty Principle that strikes ...
3
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2answers
33 views

Why the Du Noüy ring method does not depend on the material the ring is made of?

Du Noüy ring method is a way to measure surface tension. Why the measured force, $$F= 2\pi \cdot (r_i + r_a) \cdot \gamma$$ does not depend on the material the ring itself is made of? Wouldn't a ...
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0answers
34 views

Terminology for 'inferring the current state of a quantum system as it evolves and gets measured out of your control'

Suppose I hand you a quantum computer in an unknown state, but running a known program. You know the program and which part of the program is currently being executed. The program tells the computer ...
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0answers
15 views

Frequency combs measurment

How is a frequency comb actually used to measure something? For example: I don't know the length of my pen, so I take a ruler and measure it -- it reads 10 cm, so now I know my pen is 10 cm. From my ...
1
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1answer
31 views

How to quantify the level of non determinism / randomness in the universe

I recently read a little about the Bell test (I'm not a physicist, but reasonably well educated) and I started wondering if there is a way to express the level of non-determinism as a single number ...
0
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3answers
48 views

Finding the random uncertainty of a set of values [closed]

Ok, for the switch-on voltage of a red LED I have the readings as follows, all in volts: $$ 1.45, 1.46, 1.46, 1.44, 1.45 $$ The mean of these readings, in volts, is $1.45$ (I rounded up to $2$ decimal ...
3
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1answer
59 views

Decoherence Free Subspaces and how they stay this way, using the Zeno Effect

I am currently reading papers discussing the Zeno Effect, which discuss how measuring a system at high frequencies can almost freeze the state of a system, or keep the system in a specific subspace of ...
3
votes
1answer
35 views

How is the total spin of a particle actually measured?

Say I have a fermion whose total spin I do not know. I then use a stern gerlach setup to measure $S_z$. If I find +1/2, I could say that the total spin is $1/2$. But it could also be the eigenket ...
0
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4answers
91 views

Measuring force of a punch

I'm trying to build a device that can mesure the force of a punch. ​ My initial plan was to build a platform with 4 springs (one at each corner) and an accelerometer in the middle. But, if the ...
15
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3answers
8k views

Home experiments to measure the RPM of a pedestal fan without special equipment?

Is it possible to determine to an approximate degree, the revolutions per minute of a fan, for example a pedesal fan pictured below, without using some electronic/mechanical measuring device? One ...
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3answers
127 views

How stellar aberration is measured?

A simple calculation shows that stellar aberration due orbital motion of earth is roughly 20 arcseconds. My questions are: Practically how this small value is measured? Does this value is in the ...
6
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3answers
1k views

Pauli exclusion principle and Entangled pairs

It is true for fermions in the same potential that the total wavefunction of two particles must be antisymmetric with respect to exchange of electrons. Which means the spin wavefunction is given by ...
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0answers
40 views

Radius of $n^\rm{th}$ orbit of an atom in terms of Bohr's Radius

Bohr's Radius$=0.529$ Angstroms My book says that the radius of $nth$ orbit of any atom can be calculated by: $$r=n^2 a_o$$ where $a_o$ is Bohr's Radius. But I think it should be given by following ...
22
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1answer
3k views

How did Rømer measure the speed of light by observing Jupiter's moons, centuries ago?

I am interested in the practical method and I like to discover if it is cheap enough to be done as an experiment in a high school.
14
votes
2answers
297 views

GHz rate single photon counting

The fluorescent lifetimes of molecules used in biological applications tend to be in the sub-ns to a few ns timescale (let's say 0.8-4). The most direct methods to measure lifetimes typically involve ...
1
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1answer
19 views

How to find the error of all the counts within the Full Width Half Maximum (FWHM)?

We've been doing Gamma ray spectroscopy and have peaks from various sources. We'd use Poisson statistics, but obviously the detector doesn't have a resolution of zero, thus we are summing the counts ...
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2answers
42 views

Could neutrinos be used to take high resolution pictures of atomic nuclei?

Of course, this is obviously not feasible with modern technology but is it theoretically possible?
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2answers
266 views

Has the speed of gravity been measured experimentally? How? [duplicate]

In Newtonian physics, changes in gravity propagate instantly. In general and special relativity, gravity propagates at the speed of light, $c$. From reading answers to questions about gravity on this ...
0
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1answer
41 views

Practicality of measuring observables

In quantum mechanics Hermitian operators acting on the Hilbert space of a system are observables. From what I understand this means that there is some measurement we can do such that the eigenvalues ...
3
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2answers
140 views

How well can we localize gravitational wave sources?

A recent question cited a story about the recent gravitational wave detection saying that we can use the gravitational wave sensing to find supernova earlier in their process of collapse: [with ...
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2answers
2k views

Does photon have size measurement because of its particle nature

Does photon have size measurement because of its particle nature like electron's 3.86*10^-13m etc..
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2answers
98 views

How to (safely) measure the surface area of a human body? [closed]

Here's a question just for curiosity. You measure mass on scales. You could measure volume by submerging in a bath with a snorkel system. But how could you measure a living human's surface area ...
0
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1answer
24 views

How could the BOE (barrel of oil equivalent) be measured?

The barrel of oil equivalent was given as an example of gigajoule scale energy. "The barrel of oil equivalent (BOE) is a unit of energy based on the approximate energy released by burning one barrel ...
0
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1answer
59 views

Calculate how many photons hitting a sample that are absorbed

In the determination of the quantum yield of a photoisomerization, $\Phi,$ the following is needed $$ \Phi = \frac{\mbox{Number of "reactions"}}{\mbox{Number of absorbed photons}} $$ The photon flux ...
2
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0answers
42 views

Venturi “Turn Down” [closed]

I'm sorry if this isn't the right forum for this question, but physics is the only stackexchange which had many results for Venturi. I'm trying to measure the flow of air through a 16mm hose/pipe ...
6
votes
1answer
70 views

Is there a tool to measure the chemical potential of a system?

Let's suppose I put you inside a room filled with a gas. You can measure its pressure directly with a barometer. You can measure its temperature directly with a thermometer. Can you measure its ...
1
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0answers
45 views

Is there any well-defined, measurable atomic size?

Is there any well-defined, measurable size at the atomic scale? I was under the impression that the van der Waals radius was a good way of describing the size of an atom, but it turns out to be a ...
2
votes
0answers
29 views

How precisely do we know the van der Waals radius of hydrogen?

I've found several sources that say the van der Waals radius of hydrogen is $120 pm$. How precisely do we know this number? What order of magnitude is the error on this measurement?
3
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0answers
59 views

Simultaneous measurement of non-commuting observables without uncertainty

A pair of non-commuting Observables $\hat{X}$ and $\hat{P}$ does not have a common set of eigenfunctions, i.e., it can not be measured simultaneously. Let us for the sake of simplicity assume that ...
3
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0answers
27 views

How are melting points of metals measured?

How are melting points of metals measured? What apparatuses are used and how do they "conceive" heat units?
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1answer
63 views

Why do scientists measure fundamental constants so precisely?

According to the last CODATA report the charge of electron is measured very precisely (10 decimal places). And it's not only about the charge of electron. Why do scientists measure fundamental ...
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7answers
806 views

Can a ultracentrifuge be used to test general relativity?

With today's ultracentrifuge technology, they can spin so fast that the sample can be subjected to accelerations of up to 2 millions Gs. That is equivalent to two solar masses. Has someone tried to ...
3
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1answer
134 views

Ideal shape of a water clock

The ancients undoubtedly discovered the ideal shape of a water clock by trial and error. In examining some ancient water clocks I notice the shape is different depending on the size. For example, a ...
2
votes
3answers
137 views

How is complex permittivity measured?

Complex relative permittivity is defined as $$\epsilon_r = \frac{\epsilon(\omega)}{\epsilon_0}=\epsilon_r^{\prime}(\omega) + i\epsilon_r^{\prime\prime}(\omega) = \epsilon_r^{\prime}(\omega) + ...