The measurement tag has no wiki summary.
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Why is it that the atom is considered invariant?
The building of physics rely on the assumption that the atom is invariant through time (*).
IMO the invariance cannot be measured in the laboratory because what happens with the atom also happens with ...
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2answers
27 views
Cheaply measuring torque required to turn small screw
The small screw is a plastic drip-line variable-flow water valve.
My plan is to glue a constant-width arm to the head of the valve, put the thing in a vise and stack pennies on the end of the arm ...
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In terms of covariance matrices, are partial measurement and partial trace equivalent?
Partial measurement and partial trace
There is a connection between a measurement of a part of a system and tracing this subsystem out. Say, we have a system composed of subsystems $A$ and $B$ in a ...
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1answer
27 views
Decibel equation, dyne or Watt
I know decibel is used as a ration between two same physical quantity on a logaritmic scale.
Is also used for calculate the intensity of a sound, but I found it reported in two different ways
db = 20 ...
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Possible outcomes of measurement on a state
I having some trouble understand a question I'm handed. I doesn't seem to be difficult, I think, but I'm having some trouble understanding what I actually have to do.
I have the following variable ...
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If the measurement of the proton size is correct and it is lower that it was expected than what are the theoretical implications?
In the press release of the recent measurement of the proton structure, they barely mention various theoretical explanations for the effect. What is the most likely (not assuming now that the ...
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1answer
101 views
Is it possible to measure the true distance between two objects? [closed]
Could we measure an accurate distance between two objects or do we get a number with an infinite amount of decimals? A number with an infinite number of decimals are an infinite amount of data, so I ...
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1answer
60 views
How does an atom look like in momentum space?
I am reading an article in a popular science magazine about atoms in extremely low temperature (condensation?). It's interesting and I've got few questions regarding this phenomenon.
1) In the ...
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Does one second exist? [closed]
Let us assume .5 second has passed. Now similarly let .9 seconds also passed..
Then let's say that .99 second has passed...we're still not done because 1 second hasn't passed.
Then follows .999 ...
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2answers
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How do you come up with a POVM?
This is a made-up example, just to understand a concept. If changing the probability values aids your explanation, that's fine by me.
Say you have a physical quantity $E$ that can take values 1, 2, 3 ...
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Physics (measurement) [closed]
In october,1707 four British warships ran aground because of error in position,sparking the effort to produce a marine clock that would be accurate to locate a position with in 30 miles after sailing ...
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physics (measurement) [closed]
The grains of California beach sand have an average radius of 50μ meter.What mass of sand grains would have a total surface area equal to the surface area of a cube exactly 1m on an edge?Sand is made ...
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Time of Measurement Vs Number of Measurements
Let's say that an experiment has to determine the number of cosmic muon at sea level. The appropriate equipment is ready to measure the counting rate.
I can think of two ways
Count for 10 minutes, ...
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1answer
39 views
How many measurements should be done? [closed]
I am measuring time of a computer operation. The operation should run roughly same time each time I measure it. How many times should I measure it to get good average and standard deviation?
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3answers
123 views
Precision of Coulomb's law
Up to which precision has the coulomb law proven to be true?
I.e. if you have two electrons in a vacuum chamber, 5 meters appart, have the third order terms been ruled out? Are there any theoretical ...
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2answers
101 views
What is known about the Magnetic North Pole's location before 1800?
I was recently startled to find that the Earth's North Magnetic Pole is moving at upwards of 40 km per year, with an additional ~80 km daily elliptical drift about its mean position due to variations ...
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1answer
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Measurement uncertainty of the quantity, that is function of two others quantities
I'm trying to compute uncertainty for the density of the ball.
I measured its radius 6 times, so I was able to compute the stastistical uncertainty (we call it uncertainty type A, I don't know, if ...
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2answers
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Is there any phenomenon in physics which is sensitive to irrational numbers?
We can measure only rational numbers by our scale. Here is an example where irrational numbers does makes sense. If so then this question may have some theoretical importance. Is irrational numbers ...
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93 views
How can we detect a black hole? [duplicate]
If black holes are phenomena of very high density (gravitational singularities) which don't emit radiation how can we detect them so far away from us where so much other radiation can hide the black ...
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projective measurement & POVM
Let us consider the following completely positive map $\mathcal{B}(\mathbb{C}^n)\ni\rho\mapsto L\rho L^\dagger$, where $L\in\mathcal{B}(\mathbb{C}^n)$ is any arbitrary operator (and can have rank ...
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1answer
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Is there a naturally occuring sound pressure level reference?
There are lots of devices that purport to measure the absolute value of sound pressure levels. Here is an example, here's another, there's also this iPhone App. Putting such devices side-by-side in ...
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395 views
Can we measure an electromagnetic field?
As far as I can check, the Aharonov-Bohm effect is not -- contrary to what is claimed in the historical paper -- a demonstration that the vector potential $A$ has an intrinsic existence in quantum ...
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Why is the Planck length the shortest measurable length? [duplicate]
I quote from the Wikipedia article on Planck length:
According to the generalized uncertainty principle, the Planck length
is in principle, within a factor of order unity, the shortest
...
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2answers
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Asymmetric uncertainties
Inspired by these two question on tex.SX
Asymmetrical tolerancing
Asymmetric uncertainties with siunitx package
I'd like to ask for a nice explanation for these kind of uncertainties, like ...
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3answers
157 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 ...
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535 views
How hot is the water in the pot?
Question: How hot is the water in the pot? More precisely speaking, how can I get a temperature of the water as a function of time a priori?
Background & My attempt: Recently I started spend ...
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About the resolution/$\sqrt{12}$ uncertainty
Suppose you want to measure a (real-valued) quantity with an apparatus which will return as a result of the measurement the closest integer to the true value of the quantity.
Then, a common use is to ...
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1answer
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Velocity of measurement
As per to Heisenberg uncertainty we will not be able to calculate the position and momentum at same instant because by the time we calculate the next of the one, it changes (i.e.) the changes are very ...
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1answer
113 views
Uncertainty in Acceleration given the uncertainty in position
I had a motion detector record the position of a dynamics cart and automatically plot Position vs Time and Velocity vs Time plots in Logger Pro on the computer. If the instrument uncertainty in ...
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1answer
77 views
Experimental perspective in understanding the Heisenberg Uncertainty Principle
I need to confirm whether or not I understand Heisenberg Uncertainty Principle. So the crucial thing is that you need an "ensemble" of measurements:
$$\delta x \delta p \ge \frac{\hbar}{2}.$$
If I ...
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1answer
366 views
Why is carbon dating limit only 40,000 years?
For an example, when they tried to get the carbon dating for presence of Aboriginal people in Australia they get to the number 40,000. But it could be much earlier. Why is that 40,000 years limit for ...
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where to find sample fluid stirring data?
I want to find some force data for fluid stirring. Originally I intended to record the data using my force sensor, but it doesn't have the resolution to read stirring force for Newtonian fluid.
...
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2answers
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Decomposing light into frequency spectrum
Light hits a charge coupled element. The wavelength of the light somehow is translated into a color picture. Where can I learn about methods (algorithms) to decompose light hitting a CCD into ...
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1answer
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Is this the correct way to I combine multiple interdependant pressure readings?
I want to measure the density in different layers of a suspension. To do this I want to place pressure sensors at different heights. Let's assume that the sensors are not by orders of magnitude more ...
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1answer
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What's the difference between 'least count' and 'smallest division'?
I'm wondering the difference between the 'least count' and the 'smallest division' of an instrument.
Can you explain that for me, plz?
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1answer
324 views
How to measure a solid-solid surface energy?
Many techniques exist to measure the surface energy between a liquid and a liquid or a liquid and a gas (see e.g. the wiki page).
Methods to measure the surface energy between a solid and a fluid are ...
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1answer
145 views
Practical method to weigh human limbs with common household items?
What methods could be used to determine (or estimate within a reasonable margin of error) the mass of a living human's limbs, short of cutting them off? And more interestingly, how can this be done ...
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1answer
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Quantum computing problem
Suppose that a qubit is in the state $|\varphi\rangle=a|0\rangle+\sqrt{1-a^2}|1\rangle$, where $a\in[-1,1]$.
If we first perform a standard basis measurement on this qubit and then perform a
...
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1answer
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Measuring acceleration of a bus using water between two sheets of glass
I was riding a bus one day and noticed that the double windows had some water between them. As the bus accelerated, the water collected to the sides, first forming a trapezoid and then a right ...
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1answer
52 views
Multimeter has a resistance
If a multimeter has a resistance (1M ohm, say) when measuring voltages how do I take that into account in my error?
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Electron mass changes with website
When particles mass can be changed by changing the website, then how to calculate with confidence?
For example:
Google: electron mass = 9.10938 188 × 10$^-31$ kilograms
Wikipedia: electron mass
...
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1answer
100 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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168 views
Setting up a local-coordinate system in space-time using only a single clock and light beams
I have a question to ask about the operationalist view of space-time. I am a mathematician who happens to be interested in physics, so if anyone thinks that my question is a silly or vague one, please ...
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1answer
160 views
Photometer: measured Irradiance L converted to photon rate
I am conducting an experiment in which the power meter reading of $410\,nm$ narrow bandpass stimulus is noted to be 30 $\frac{\mu W}{cm^2}$ at a distance of 1 inch away from the light source.
I wish ...
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765 views
Is it possible for a physical object to have a irrational length?
Suppose I have a caliper that is infinitely precise. Also suppose that this caliper returns not a number, but rather whether the precise length is rational or irrational.
If I were to use this ...
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1answer
115 views
Finding radius of Earth through observation of Sun's motion
The question I'm about to pose is from a physics book I had recently bought. Since I am very interested in physics I am quite keen in understanding how this question can be solved. Before I present ...
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Experimental data for gas flow through pipelines
Maybe some of you could point a good source of experimental data of gas flow through pipelines? What I need is a very simple flow of some gases through some diameter simple linear pipeline. A graph of ...
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353 views
How to calculate uncertainties of a natural exponential function?
(I apologize if this should be posted in mathematics, however I chose to post it here as it's technically about physics)
I conducted an experiment in which position of items were shifted on an ...
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1answer
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Measuring the quantum state of light
A clarification please
The following scheme to measure linear polarization states (a single polarizing beam splitter and two photo counters) orientation (as $arctan \sqrt{\frac{v}{h}}$) of coherent ...
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Measurement in Quantum mechanics
I have got a quantum conservative system whose Hamiltonian is $H$. I consider an selfandjoint operator $O$ whose eigenvalues and eigenvectors are: $$O|\psi _{n}\rangle = \lambda _{n}|\psi ...
