The result of sampling the property of a system

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1answer
27 views

Are there any industry usage for gas thermometer? [on hold]

I've been searching on this for a while now. Are there any specific advantages and disadvantages for using gas thermometer? Are there any specific industry usage for this kind of thermometer?
0
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4answers
98 views

Is there an official list of independent units of measurements?

When I say 'independent units', I mean those which cannot be broken down anymore, and simultaneously forms the basis for any more, complex measurements. For example, height, length, and width can all ...
2
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1answer
37 views

What are the tools used by Newton to measure motion?

I was wondering how did Sir Newton measured motion of objects (non celestial ones). What was his toolskit at the time?
0
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1answer
106 views

Can conductivity (or resistivity) value be assigned to 2D materials?

2D materials, such as graphene monolayer or graphene nanoribbon, don't really have a cross section. By definition, conductivity is $\sigma = \frac{J}{E}$, and $J$, the current density, is calculated ...
0
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0answers
7 views

most efficient set of weights with whole number mass to n-power for balancing unknown mass on vertex of regular triangle

I saw this qustion: http://puzzling.stackexchange.com/questions/186/whats-the-fewest-weights-you-need-to-balance-any-weight-from-1-to-40-pounds Suppose you want to create a set of weights so ...
3
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3answers
68 views

Projection operators in quantum mechanics

I'm reading a book on quantum mechanics and a topic in there was not well explained. I couldn't find an answer on the web. Say $\psi(x)$ is a position wave function of a one dimensional free particle,...
-1
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5answers
142 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 ...
0
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0answers
12 views

Using a magnetometer in a sub-sea application, how to get a good magnetic bearing?

Mechanical engineer here, getting in over my head concerning magnetic sensors, electronics and the like :-) Quick situation description:For a work-application I am looking at using a MEMS based 3 ...
4
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4answers
294 views

Non linear QM and wave function collapse

I heard that there have been some propositions about describing the collapse of the wave-function by adding non-linear terms, but I couldn't anything in any any textbooks or even articles (probably ...
1
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0answers
21 views

How to determine the three-velocity measured by a single observer?

In this question the issue of extracting the three-velocity of a test particle in some frame arose. The answer provided by @PaulT and in this paper (arXiv) seems to me to give rise to ambiguity when ...
1
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1answer
45 views

Entangled qubit measurement

I came across this while reading lecture notes and I have no idea how they got the $M_0$ and $M_1$. The way I see it, the matrix $U$ is a block matrix: $$ \left[ \begin{array}{ c c } P &...
8
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1answer
74 views

Have we measured the rate at which Jupiter is shrinking?

On most websites that I looked at, it says Jupiter is shrinking 2cm/year (for example wikipedia and Quora). However neither of these website say whether this rate is measurable (the latter says it is ...
0
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2answers
141 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 ...
2
votes
2answers
705 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 ...
1
vote
1answer
239 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 ...
0
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0answers
25 views

Antenna measurements and parameters calculation

Lets suppose we have some data collected from antenna measurement. For every theta and phi point in any coordinate system ( here refering to Ludiwg coordinate systems II and III) the data can be ...
7
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5answers
2k views

Measuring the speed of light and defining the metre - absolute or relative?

If the metre is now defined as the distance light travels in vacuum in 1⁄299,792,458th of a second and the speed of light is accepted to be ...
-3
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0answers
19 views

Uncertainty principle-QM [duplicate]

I some trouble understanding the uncertainty principle. I understand most of the math derivation but not the physics. Is there any intuitive explanation of this idea, and why is the uncertanty does ...
4
votes
1answer
76 views

Does a measurement always require the exchange of energy?

Can you measure something about something without adding or removing energy from it? This comment has got me wondering if there is a way to measure a property or a quantity of something without some ...
3
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1answer
135 views

How to read numbers reported in this LIGO paper?

I am not sure how to read the numbers in this excerpt from the abstract of GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence: Are the +/- small ...
2
votes
1answer
46 views

How to measure relative phases of quantum states

If I have a large number of identical systems in identical quantum state $\Psi$ and an observable $A$ whose eigenstates are $\alpha_n$: $$ \Psi = \sum_n c_n \alpha_n $$ I can get absolute values ...
1
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1answer
34 views

How the data or models given in physics or mathematics problems can be obtained in real life? [closed]

When ever there is physics or mathematics problem. we are already given a mathematical model. Can't we make own models from given diagrams or data collected from the problem? sometimes angle is given ...
4
votes
2answers
169 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 ...
3
votes
1answer
33 views

What are the effects of compositional changes in a thermocouple's junction?

We use thermocouples (type B) to measure the temperature of metals (Fe, Ag, Pd, etc) in a furnace under pressure. We weld two thermocouple wires together using an arc welder. This junction then comes ...
1
vote
2answers
73 views

Error Analysis involving random errors

The question goes like this: In an experiment, the time period of an oscillating object in five successive measurements is found to be $0.52$s, $0.56$s, $0.57$s, $0.54$s, $0.59$s. The least count ...
1
vote
1answer
40 views

How to find the covariance matrix after a partial homodyne measurement?

The Gaussian state of two modes, with quadrature operators $X_1,P_1,X_2,P_2$, is given by a displacement vector $d$ and covariance matrix $\sigma = \begin{bmatrix} Var(X_1,X1) & Var(X_1,P_1) &...
3
votes
1answer
73 views

How can I measure the amplitude of a light wave?

Suppose I have a light wave and I want to measure its amplitude, or check to see if it has an amplitude of a certain value: how would one go about doing this?
4
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2answers
61 views

Combining two data points with different uncertainties

I have two separate algorithms (call them "A1" and "A2") which reconstruct the $(x, y)$-position of an event in a particle detector. I can test both of these algorithms on simulated events from a very ...
0
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5answers
268 views

The measurement of electricity

I'm a student trying to understand electricity. As I learned from school, electricity is the flow of electrons, but I'm confused about the measurement of electricity. As I learned, voltage is the "...
0
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0answers
36 views

Does the definition of the metre have to take into account spacetime curvature?

The definition of the metre is: The metre is the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second Does this have to be modified in a ...
1
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1answer
30 views

Systematic+Random Uncertainty for velocity measurement

I have a question regarding systematic and random uncertainties. I have to measure the mean value of a velocity measurement in flow field at a point. I've recorded say 1000 samples in time, which I ...
1
vote
1answer
69 views

How to measure the mass and balance point of a human forearm?

I've been trying to find this out for about a month now. I'm usually met with humorous but not really helpful comments about chopping my own arm off. I'm preferably looking to do this on a budget ...
7
votes
1answer
662 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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3answers
60 views

Is there a way to measure the thickness of a metallic plate of order of micrometers?

I have a $5 cm×5 cm×? \mu m$ copper plate. Where '$?$', the thickness of the plate, is really small (about 30um). Is there anyway using physics to calculate the thickness? Update: Sorry I forgot ...
68
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5answers
6k views

How do laser “tape measures” work?

There is a device available for about $\$40$, which fits in the palm of the hand, runs on two AA batteries, and can measure distances up to $50\,{\rm ft}$ to an accuracy of $\sim \frac{1}{8}''$ ($\sim ...
4
votes
4answers
243 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 $|\psi\rangle$...
5
votes
2answers
129 views

Is wavefunction collapse “global”?

I have the feeling that the premises of this question may not be coherent (so to speak), but here goes: Suppose we have a system $X$ in a quantum superposition between states $0$ and $1$, say, with ...
0
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1answer
28 views

making sense of measures in electronics

I am in secondary school in the UK, and at this point in physics the information we are given is very vague at a fundamental level. My main concern is with electricity and circuits, and the measures ...
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0answers
45 views

Estimate heating wires temperature

Im design a power supply to work with heating wires and one of the task is to estimate the temperature of the bare wire for a given current or power consumption. I've tried to measure the ...
1
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1answer
59 views

Measurements in quantum mechanics

Why does measurement change things? I read that measurement changes things because we have to bounce photons off an object to 'see' it and that changes its position, momentum etc... But on the other ...
2
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2answers
65 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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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
votes
4answers
528 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
965 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
votes
1answer
28 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 (wavelength/...
3
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1answer
88 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
62 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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0answers
25 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). ...
4
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0answers
58 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 ...