Questions tagged [measurements]
The measurements tag has no usage guidance.
844
questions
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Thermal radiation measurements: Looking for ~100 Hz BW, broadband (1-20 um) NIR/MIR detector
I am looking for a detector with about 100 Hz bandwidth, that has broad and ideally uniform absorbtance in the 1-20 um range. I need to be able to pickup signals in the 1 uW range with SNR >10, ...
0
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1answer
34 views
Uncertainty in measurements with a ruler,
I am using a 30 cm ruler with a resolution of 0.1cm (1mm). I measure the length of a side of a cube with sharp edges. I keep the ruler against the side of the cube and take two readings from the ruler....
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1answer
51 views
How to work out the size of the earth from standing on a seaside cliff? [on hold]
I read in a book that it is possible; given that you know the distance between you (on the cliff) and a buoy (in the water) that you can see in a distance.
1
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0answers
18 views
Stern-Gerlach: would QED treat it as many discrete virtual-photon interactions?
If yes, how many? And in the region of few interactions, does that correspond to a “weak measurement”?
(I come to this question while learning about decoherence. We usually think of entanglement for ...
122
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22answers
11k views
How do I experimentally measure the surface area of a rock?
I hope this is the right place to ask this question.
Suppose I found a small irregular shaped rock, and I wish to find the surface area of the rock experimentally. Unlike for volume, where I can ...
1
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0answers
21 views
Significant number determination
Expressing magnutitudes with units and significant numbers which reflect the sensitivity of our measurement devices seems to be important in physics. When adding/ subtracting two numbers we report the ...
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0answers
56 views
The thermodynamics associated with conditional probability?
So I'm quite confused by an answer: https://physics.stackexchange.com/a/510626/150174
Let $|\psi\rangle$ be the initial state, and let $U_t=e^{-i Ht}$ be
the evolution operator, assuming a time-...
2
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0answers
40 views
The $2$'nd law when a subsystem's entropy decreases due to a measurement?
Background
So let's say there's system $1$ and system $2$ where system $1+2$ is an isolated system.
Let the density matrix of system $2$ be:
$$\rho_2 =
\begin{pmatrix}
3/4 & 1/4 \\
1/4 & ...
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0answers
15 views
Pegging a number to the when the measurement happens?
Motivation
Usually the measurement is denoted by for example:
$$ \alpha |0\rangle+\beta |1\rangle \to |1\rangle $$
Note that there is no mention of when this measurement happened. I was wondering ...
2
votes
1answer
38 views
Measuring sound waves with lasers
I've recently been learning about recording techniques for music production, and I was surprised to learn that there are only three types of microphones in wide use (dynamic, condensor, and ribbon), ...
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0answers
18 views
Converting IMU measurements to that of a “virtual” IMU aligned with another frame on the same rigid body
Suppose that on a rigid body/object, we mount an IMU (inertial measurement unit) that measures the angular rate $\omega \in \mathbb{R}^3$ and the acceleration $a \in \mathbb{R}^3$ from the gyroscope ...
3
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1answer
50 views
Measuring mass density of electrons in the universe
Pardon me if the question is too naive, but only baryon and dark matter masses are considered while making measurements of the mass density in the universe.
What I am interested to know is how small ...
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1answer
40 views
How LHC sensors work? [closed]
newbie here. I am here because after working with Raspberry Pi sensors and Analog to Digital converters, and computer processors, I wondered how exactly do sensors in large scale physics experiments ...
0
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2answers
69 views
When did scientists first experimentally measure wavelengths of EM radiation? How? [closed]
When did someone first discover that short wavelength light has higher energy than long?
And can gamma ray wavelengths be measured, even today?
1
vote
1answer
25 views
Error estimation with missed data
When I need to find an error in the value of some real physical quantity and I can have as many number of measurements as needed, then it is clear. For example, I have a metal rod 10 cm length and 1 ...
2
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1answer
47 views
What can be measured in quantum mechanics and how?
This is a question about bridging reality to theory.
In learning QM theory, we learn a bunch of stuff about observables, like their operators, that two quantities can be measured at once if their ...
0
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1answer
100 views
2019 Higgs Boson Mass?
Wiki, based on the 2018 Particle Data Group, gives the Higgs boson mass as $125.18 \pm 0.16$ GeV$/c^2$. OK.
However, 2017 ATLAS gives a combined value of $124.98 \pm 0.28$ GeV$/c^2$.
So what is ...
0
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1answer
16 views
Is it possible to measure the amplitude of a magnetic field independent of the orientation?
The strength of a magnetic field can be measured as strength in a specific direction.
We can calculate the strength of a magnetic field along the field lines from measuring the strength in x,y,z ...
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2answers
30 views
Light Polarizer for Photons
This is maybe a noob question. I read that if unpolarized light is passed through a polarizer that only allows vertical polarization, then if this light is passed through a diagonal polarizer, only ...
1
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1answer
22 views
Does a maximum thermometer assume a room temperature?
Consider a liquid-in-gas maximum thermometer. That is usually conventional thermometer designed for measuring body temperature.
Wikipedia says:
One special kind of mercury-in-glass thermometer, ...
-3
votes
3answers
142 views
Why are speeds of different EM waves in vacuum not EXACTLY equal?
It is said in my textbook (reference below) that the different waves of the Electromagnetic Spectrum have velocities almost equal to each other. (Variations are within a few m/s according to my ...
3
votes
1answer
84 views
How to know that scientific instruments work?
While reading Zimring's book, What Science Is and How It Really Works, I came across some words on being skeptical about scientific instruments on p.183-184:
"The extent to which such instruments ...
1
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1answer
18 views
Uncertainty and error in a measurement
I do not find a clear and simple explanation of the difference between uncertainty and error of a measurement.
Basically, in a measurement, uncertainty is defined as the standard deviation of the ...
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1answer
32 views
Significant figures and precision
Which of these two measurements is more precise, 5.1 cm or 0.002 ? As per concept of significant figures 5.1 cm is more precise because it has two signicant figures while the other oone has just one
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0answers
28 views
Principle of a pyrometer
How does a pyrometer work? Especially how do I ensure that the temperature of a single spot is measured (where the laser points at)?
Here is a scheme of the structure but I guess it's not really ...
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3answers
42 views
Are interference patterns the basis for all other measurements of light frequencies and wavelengths?
The wavelength or frequency of monochromatic electromagnetic radiation is determined indirectly by calculations on the interference or diffraction pattern. These patterns are generated by gratings, ...
20
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4answers
1k views
How is the speed of nucleons in the nucleus measured?
This article claims that "nucleons in a dense nucleus exceed 25 percent of the speed of light".
How do you measure or infer the speed of nucleons in the nucleus?
Note added later: I'm looking here ...
0
votes
1answer
26 views
Why does a photomultiplier tube (PMT) traditionally present better signal-to-noise ratio (SNR) than an avalanche photodiode (APD)?
Empirically, a photomultiplier tube (PMT) is said to present better signal-to-noise ratio (SNR) than an avalanche photodiode (APD). Some materials say that it is attributed to the higher gain and ...
0
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3answers
47 views
Use of significant figures in lab report calculations
I am currently doing a lab report that involves multi-step calculations. The values σ(mean, visual) and σ(mean, auditory) are calculated to be 0.004051s and 0.004917s. Since the number of trials (27 ...
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0answers
12 views
Methods of Subnanometer Distance Measurement
How can one measure distances down to the ~0.01nm resolution using standard equipment such as LEDs, lasers, photodiodes, interferometers etc...?
A pulsed diode could be used as a measurement device ...
0
votes
1answer
22 views
Is Bourdon tube affected by the cross sectional shape of the tube?
I've been searching for the working of pressure measuring tools , and i know that what makes the bourdon tube straighten is the distribution of the pressure on its walls .so
my question is , in ...
1
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1answer
59 views
What does “An experiment performed with certainty has results with uncertainty.” mean? [closed]
A physics book says:
An experiment performed with certainty has results with uncertainty.
What does this mean?
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1answer
36 views
Measuring acceleration due to gravity in the lab
I am measuring the acceleration due to gravity in the lab with an electromagnet apparatus.
My textbook says to take the average time for a number of falls (keeping the height constant of course).
...
0
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1answer
29 views
How to measure the microscopic surface area of a textile?
How to measure the microscopic surface area of something like a piece of cloth?
By microscopic, I mean on the level of fiber surface, not the area that would be measured by using a ruler on the piece....
0
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0answers
16 views
Transformation to get rid of distribution multiplets
Are there any well-known distribution transformations that account for doublets, triplets, higher multiplets due to time series independent peaks occasionally being too close to resolve? I feel like ...
2
votes
0answers
55 views
How to estimate the mass of an incoming asteroid?
A second galactic visitor has just been observed: see this link.
For a mass which is small enough to have no noticable effect on other masses, is there any other way to infer the mass? Its own motion ...
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1answer
53 views
Changes to Planck constant historically [closed]
I looked all over to get the various accepted value of the Planck constant since 1900. But there is never any record about the history of this mysterious number.
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1answer
36 views
How to build a particle detector, given a desired probability of detection [closed]
Suppose that the average flux of cosmic rays at sea level on an horizontal surface is $$\varphi = 1\, {\text{cm}}^{-2}\,{\text{min}}^{-1}$$
and that we can take this value without error.
What should ...
0
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1answer
153 views
How many worlds are there during branching in the many worlds interpretation?
Background and Question
"Measurements are modelled as interactions between subsystems of the universe and manifest themselves as a branching of the universal state." - Wikipedia
What is the ...
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0answers
36 views
How did people estimate the speed of light before modern technology? [duplicate]
I just read a wikipedia page on the speed of light. Apparently people have made pretty accurate estimates for almost 200 years. How did they do this? How did they measure any fundamental constant ...
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1answer
130 views
The problem of measurement in general relativity
I am looking for a good selection of articles and books on the topic of measurements in general relativity. The only one I'm really aware of is Reichenbach's "The Philosophy of Space and Time", which ...
0
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1answer
50 views
Does the length of wire affect?
I find the voltage of electric wire in between point 1 and point 2. I want to know if I use the differrent wire,long one and short one,the voltage will be equal or not?
0
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1answer
59 views
Strange anomaly in the calculation of the cosmological constant
I was trying to calculate the cosmological constant with two different methods proposed on the internet, that are apparently equivalent but they give different results and different dimensional ...
0
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3answers
173 views
Why nature rejects 100% accuracy in experiments? [closed]
I have never heard about any experiment performed which is 100% accurate (Sorry,if there is any).By the term accurate I mean accurate measurements involved in the experiment.Is it every time that an ...
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1answer
38 views
Measurement of Changes in the Weight of a Heavy Object
I am searching for an elegant way to measure small changes in the weight of a heavy object (a potted tree) over the period of one year.
However, I do not need to know the exact weight of the heavy ...
0
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2answers
55 views
Entropy of measurements; is the Von Neumann entropy lying?
Pre-measurement
Let $\left| \psi \right>$ be a pure state:
$$
\left| \psi \right> = a \left| 0 \right> + b \left| 1 \right>
$$
The density matrix of $\left| \psi \right>$ is:
$$
\...
-1
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1answer
45 views
How to locate where a ball hits the ground? [closed]
I want to locate a small ball when it hits the ground before it rolls or bounces. Consider a robotic gun fires a plastic pebble at an angle like artillery. The ball flies in the air about 0.5 seconds ...
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1answer
39 views
Visualizing Uncertainties
I am making an uncertainty exercise from a simple Physics experiment based on deriving the equivalent spring constant for a series combination of springs. The mathematical model for the combination of ...
0
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1answer
61 views
Why Does a Resistor's Resistance Vary?
Whenever we try to measure the resistance in a multimeter, the value is not the same for all measurements. Slight variations are observed over several measurements. But why this happens? And can this ...
2
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0answers
53 views
What caused the first measurement to the universe?
I've been bumbling with a question recently. People postulate that with the give model of big ban, particles forms and breaks and eventually became what we saw as of today.
However, if we put ...
