The result of sampling the property of a system

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2
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2answers
51 views

Where to measure?

In all my experiments (at the university) so far, I nearly always took my measurements on an equispaced grid over the whole measurement space. And now I asked myself, why? Is there a theory of where ...
2
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2answers
149 views

Differences in measurement between quantum physics and classical physics?

I know that there are differences in measurement due to quantisation, probability, and collapse in quantum physics, but I am having trouble explaining how these ideas relate to measurement in an ...
0
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0answers
36 views

Basics of experimental error 'bookkeeping'

In scientific experiment, I know that it is very important to know the exact level of error contained in a result, but I am not sure what the correct procedure is to 'keep book' of these errors. I ...
2
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1answer
48 views

Measurements and errors

I've measured several values of $V$ and $I$ in a simple circuit to determine de value of a resistance $R$: $$R=\frac{V}{I}$$ I have a list of points $(V,I)$ with their corresponging error (from the ...
2
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2answers
268 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 ...
2
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2answers
137 views

Does infinite actually occurs?

I tend to deny any claim that $X$ is infinite, where $X$ is anything from our observable universe. For instance: The number of grains of sand on Earth is infinite? No, it is a big number but not ...
2
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1answer
65 views

Do we regularly measure and update our physical constants (By using the LHC)?

This question is motivated by sheer curiosity. I certainly do not expect that the free parameters we use in the standard model have changed in value since we started measuring them with a "modern" ...
0
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2answers
121 views

Why is a silicon ball with an exact number of atoms a bad measure of mass?

I have some friends that are talking about why a silicon ball with an exact number of atoms is a good/bad measurement of mass (1kg) and things are getting pretty exotic. Is there a layman's ...
0
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1answer
71 views

Are measurements of time and distance independent or always coupled by the speed of light

In texts about special relativity the light clock is usually described as a tool to measure time $t$. It counts how often light travels along a given distance $d$, i.e. $t = d/c$, where $c$ is the ...
3
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1answer
271 views

How can the orbit of Jupiter's moons be used to calculate the speed of light? [duplicate]

How can the orbit of Jupiter's moons be used to calculate the speed of light? It seems this was one of the first methods and goes back to 1656.
4
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4answers
239 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 $|\psi\rangle$...
0
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0answers
12 views

Measuring Charge Density

I am running tests with metal electrodes and I am trying to find a value for charge density which I can use in calculations. If I have two vertical electrodes across which I am applying a voltage, how ...
1
vote
1answer
57 views

How might we measure the size of a proton? (Without high energy collisions) [closed]

What methods could we use to measure the diameter of sub-atomic particles. Please think of something inventive, like an indirect technique. Or name some of the lesser known techniques that have been ...
1
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0answers
132 views

What are the longest half-lives we can detect experimentally? What stops us going further? Are we trying to?

Xenon 136, apparently, has a half-life of 2.11×1021 years. This strikes me as a humongously long time to run an experiment, clocking in at about 11 orders of magnitude longer than the age of the ...
0
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1answer
120 views

Simultaneous measurement for quantum entanglement

In the simple example that we measure the spin of two entangled particles, we measure one to have spin up so we know the other has spin down. If we could (theoretically) measure both particles at the ...
0
votes
1answer
28 views

Is there any restriction on the ability to measure the full quantum state of a system without inducing backaction?

Suppose an arbitrary quantum system is in the state $ \mid \Psi \rangle $, which may or may not be a function of time. An initially ignorant obsevrer would like to figure out what $ \mid \Psi \...
0
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2answers
47 views

Packets of information in the real world

Please excuse this apparently naive question. no one appears to have the answer. If a standard packet of data is travelling down a standard fibre, what is the physical time taken between the first ...
1
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0answers
102 views

Can I measure distance with sound through soil?

Can you measure distance (cca. with precision 0.1m-1m) with sound through soil. I know this is really crazy think to do, but I have this idea quite for a while. Basically I will set speakers on fix ...
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3answers
102 views

Does really m^3/m yields m^2? [closed]

Apart the evidence that such assumption works in physics formulae, how can someone make a statement like that? Maybe the formuale works just because are worked around that assumption? Why phyicist do ...
0
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1answer
282 views

How do we measure thermal energy?

My textbook says "The amount of thermal energy is found by measuring the temperature of the substance." However, how is this true? Temperature measures only the average kinetic energy of the particles ...
0
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1answer
47 views

Rules of thumb for estimating visual angles

Tonight I've looking at an optical phenomenon presenting as rather large ring around the moon. I'm thinking it's probably a 22 degree halo, but it seems kind of big... maybe 46. Anyway, I realised I ...
1
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0answers
47 views

Can a Bell state measurement be described in the Von Neumann measurement scheme?

I have been reading and studying this article recently about non-local weak measurements and quantum erasure. Usually the weak measurement formalism is described using the Von Neumann scheme for ...
0
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1answer
51 views

Relative uncertainty blows up near offset

I'm looking to calculate the relative uncertainty for a magnetic field measurement. My device takes an initial reading but then performs operations on this using its calibration parameters. My ...
-1
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8answers
5k views

How to measure the diameter of a thin wire? [closed]

I'm working on a project and I need to measure the diameter of a thin bare copper wire but I don't know how. Can you please tell me a way to measure the diameter of a wire? Can you give me a way, ...
1
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0answers
53 views

Information and entaglement via determination of the first's system state with interaction

Could we have entangled systems (microscopical or macroscopical) and construct a way of altering the state of one of the two entangled parts (let's say by Alice) via interaction and thus making the ...
0
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0answers
105 views

How accurate is the Callendar-Van Dusen equation?

... over 0 degC to 100 degC? The equation itself can be found here I can do a very accurate one point calibration of a 1/10 DIN PT100 sensor at 0 degC. If I use the equation to correct for non-linear ...
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0answers
67 views

How do scientists measure miniscule constants like the mass and charge and speed of an electron?

What can measure the extremely tiny mass of an electron? Is it through indirect means? The same goes for charge. The pull of a single electron must be infinitely small. And if one is to attempt to ...
2
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2answers
82 views

Stern-Gerlach apparatus, measurement problem? [closed]

Consider the diagram below: It is 3 Stern-Gerlach apparatus along with some 'lenses' (illustrated here by lines). Question What would the output at A and B be? Additional information The ...
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1answer
2k views

Vernier Caliper the principle behind it [closed]

I know how to use a caliper but on what principle does devices like caliper and screw gauge works. Can someone derive its formulae. I am more or less interested in its mathematical aspect.
0
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1answer
62 views

How does one measure the state probabilities of a 2 level Hydrogen atom qubit?

I have been struggling with trying to understand how one could measure the probabilities of a superimposed Hydrogen atom's two energy states. Say the atom is in a superimposed state: Psi = a|0> + b|1>,...
2
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0answers
39 views

Limits on the information obtained through optical measurements

Consider a Gedankenexperiment shown in the figure below. There are two lasers $S1$ and $S2$ with exactly the same specifications on paper. In practice, they are of course somewhat different but ...
1
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1answer
223 views

How can I measure a length of over 4 feet to an accuracy of 1/100th of an inch?

How can I measure a length of over 4 feet to an accuracy of 1/100th of an inch ? I want to make several metal standard bars of a particular lengths, some of which are over 4 feet and I want the ...
6
votes
5answers
1k views

Number of significant figures

I am looking for an intuitive answer that will explain me why there are only two significant figures in say the number 1500. Also definition from wikipedia: The significant figures of a number ...
2
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4answers
71 views

Is there a maximum accuracy for positions in the universe?

I was thinking how, since an object in our universe can move from one position to another, it must have passed through all the positions between those two positions. (I am thinking it moved it a ...
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0answers
33 views

What is source of Infrared Radiation from some solid object? [duplicate]

I use a Fluke infrared temperature measurement meter for various applications. I have not thought too much about the source of that infrared radiation until recently. Assume some solid with maybe a ...
4
votes
2answers
101 views

How to measure temperature of a laser cooled sample at picoKelvin temperatures?

I'm reading about laser cooling.. my question is: how can the temperature of the sample be measured? (using laser cooling we can reach $10^{-12}K...)$
0
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1answer
78 views

Question about the double slit experiment

If we measure a particle before it passes through the slit, would we see the particle or the interference pattern on the screen after the slits?
1
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1answer
77 views

Compatible Observables and Measurement

Suppose $A$ and $B$ are compatible observables (i.e. $[A,B] = 0$). We take the eigenkets of $A$ to be $|a_1 \rangle \ldots |a_N \rangle$. Further, we suppose that the first $k$ eignekets of $A$ are ...
0
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3answers
12k views

How do we measure mass?

How do you measure mass? Weight is easy using a scale, but we can't measure mass that way, because then mass would be different on every planet. I know there was a Veritasium video (here) on defining ...
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0answers
31 views

Measurement of two qubits in a tensor product space

I understand that if we have two qubits, say $\Psi \in \mathcal{H}_1 \bigotimes \mathcal{H}_2$ where Alice has the first qubit, and she makes a measurement and ends up with the state $\phi \in \...
2
votes
1answer
108 views

How to measure the fineness of a textile fibre by diameter and fibre length?

I measured the diameter (um) and the fibre length (cm) of different (loose) textile fibres and have an average. Now there must be a relation between these two factors that gives an idea of the ...
2
votes
1answer
284 views

Problem on Einstein - de Haas experiment

I am a Physics student (4th year) and I'm trying to study the Einstein - de Haas effect in laboratory. That is what I got: a suspended Iron cylinder with about 5 cm height and a radius of 0.8 cm is ...
1
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1answer
202 views

Do subatomic particles have finite size?

We know atoms are mostly "made" out of empty space, so the nucleus and all the subatomic particle are very small in compared to the magnitude of the atoms. We also know that atoms are incredibly small,...
0
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0answers
25 views

How does one measure the power factor?

How does one measure the power factor? $$\text{power factor}\equiv\frac{\text{power}}{|V||I|}=\frac{R}{\sqrt{R^2+(1/\omega^2C^2)}}$$ for an RC circuit driven with $V(t)=V_0\cos{(\omega t)}$.
0
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2answers
2k views

Good way to compute the force of a hammer blow?

What is a good and easy way to compute and/or measure the force of a hammer blow, not using any fancy or specialized equipment? If the hammer is swung by hand through an arc, it is not obvious to me ...
4
votes
2answers
1k views

Do the copper connectors we used in measuring the resistance of a wire contribute to the said measurement?

We measured the resistance of a wire by setting the multimeter to ohmmeter mode and connected the ends of the ohmmeter to the ends of the wire; and we also calculated the theoretical value using a ...
1
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1answer
147 views

What is the difference between zero background radiation and field background radiation in Nuclear Physics measurements?

Can someone please explain the difference between these two terms (Zero Background Radiation and Field Background Radiation) used in radiometric prospecting measurements?
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5answers
166 views

The nature of measurement

Does the measurement of the particle change it's physical state? Or does it only seem to do that? Ex. if a particle was measured before the slits, would we see an interference pattern, or a particle ...
7
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1answer
2k views

How do bathroom scales measure body fat percent?

My bathroom scale has 2 metal strips each for a foot and the producer claims that it can measure body fat percent. There is a warning in the manual, that if I have heart problems (I guess pacemaker), ...