Questions tagged [measurements]
For questions related to methods, analysis, accuracy, presentation, or interpretation of measurements. It is not intended for abstract quantum measurement questions such as how a wave function collapses during measurement or how the Heisenberg uncertainty principle constrains quantum measurements.
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Calculating temperature when it is lower than your thermometers can read?
We have an old freezer. I believe the thermostat is broken and think it may run all the time. Food in it gets really cold (Ice cream like concrete). I've tried measuring the temp with a freezer ...
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Absent matter, is there a difference between a timelapsed cold, diffuse, large region and a realtime hot, dense, small region? [closed]
Suppose we have an arbitrarily well-isolated empty region which we initialize with a cold, diffuse, homogenous photon gas, such that the only energy density gradients are random thermodynamic ...
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Measuring Stokes parameters leading to a degree of polarisation greater than one
I am trying to measure the stokes parameters of a laser beam using the rotating waveplate method detailed here:
https://pol3he.sites.wm.edu/wp-content/uploads/sites/50/2020/01/measuring-Stokes-...
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Apparatus to measure one ampere
The following definition of the Ampere was codified in 1948 at the 9th CGPM (Conference Général des Poids et Mésures)
The ampere is that constant current which, if maintained in two straight parallel ...
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How do they precisely locate the marker at the *"true"* geographic South Pole?
So referring to this page (I'm sure there are others), they say
"A metal marker is placed at the geographic South Pole on January the 1st each year and the pole is moved usually by about 10m as ...
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Help with sourcing a specific type of integrating sphere
I am looking for a specific type of integrating sphere that can be used to capture diffuse reflectance measurements, and I would appreciate help with locating a commercially availably version of this ...
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Does a quantum measurement change the state in the past? [closed]
Consider the following very basic quantum mechanics experiment.
At time $t_0$, a system $S$ is in superposition of two orthogonal states $|A\rangle$ and $|B\rangle$, which we could describe by $\frac{...
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Is there any measurement of electron spin that doesn't involve magnetic moment?
So the way to measure electron spin is to split the beam with a magnet to obtain two beams. Essentially what gets measured is magnetic moment, that is later interpreted as the direction of spin ...
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Ensuring Regularity of Time pieces [closed]
Physics defines, I'm told, that time is "whatever" the clock measures. Time is a measurement means it has to have a unit. So let s (seconds) be the unit of time.
If time measurement is ...
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Mass, time and length are measured with 5% accuracy each, what will be the total accuracy in torque? [closed]
I don't understand the solution of the above question, the solution i know is :-
Accuracy in torque = [M%] + [2 × L%] + [2 × T%]
Which will be equal to 25%
I dont understand why 2 was multiplied to L% ...
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Measuring reflectance of a non-planar object w/ an integrating sphere
I am designing an experiment to measure the reflectance (diffuse+specular) of insect specimens, and I plan to use an integrating sphere to collect the measurements. Typically, I have seen that ...
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What is the minimum temperature difference which can be measured?
All real things have temperature. Temperature can be measured in various ways. We have reached to a great precision in measuring change in time and space , however I am not sure to what extent change ...
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Does that the regularized sums of series and integrals divergent to infinity appear in measurements prove that they represent actual infinite values?
There is a philosophic debate about whether there could be infinite quantities in nature.
Definitely we cannot measure infinite quantities with measurement instruments.
But we know the regularized ...
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What exactly is a "measurement" in quantum mechanics?
*I can't see immediately whether or not this post constitutes as a duplicate, but I wouldn't be surprised if it does. If that is the case, then please reference me the post that I'm duplicating so ...
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Curve fitting and error propagation for non-independent quantities
I have measurement values $y_\mu$ at times $t_\mu$; the should follow a function $y(t) = f_t \, \cos (\Omega_t\cdot t - \delta)$ where $f_t, \Omega_t$ are slowly varying functions (currently I am ...
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How to measure time varying electric field strength accurately in space and time?
I would like to know of any techniques that can be used to measure the electric field strength precisely and accurately in both time and space. I know that there will be physical/ practical ...
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Measurement Uncertainty of Correlated Quantities
Using a Thorlabs S310C Detector with a calibration error of ±5%.
Let's say I do two measurements of laser power with this detector over a time period of 60s. The first measurement is bare input power, ...
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What constitutes a measurement?
In an intro quantum mechanics textbook theres some experimental/historical background, then the postulates are stated, then the rest of the text focuses mostly on the math. But there’s one issue I’ve ...
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Calculating average from several independent physical experiments
If I have 2 experiments measuring the same thing. For example, I measure the voltage with 2 different tools (2 different voltmeters). I can calculate the final average in 2 different ways. For example,...
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The "observer effect": is this a basic law of every observation or measurement? [duplicate]
I would appreciate some clarification of the "observer effect":
Is it generally true that every observation (or measurement) disturbs the object being observed?
I understand the observer ...
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Connection between quantum non demolition measurement and the Heisenberg limit in metrology
Quantum non demolition measurements are those that do not feed back action noise into the measured observable. For discrete systems, this leads to the somewhat trivial case of where the observable (...
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Measurement paradox
When building electronics to measure usually it is asked what the bandwidth of the signal is and what is the frequency range usually done to limit noise bandwidth and thus have more SNR. To me it ...
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Measurement problem and precise mathematical calculation
The infamous measurement problem is a problem in the foundations of quantum mechanics: different people have different views how to understand this problem: some people even deny that there is any ...
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Significant figures in simple calculations
I have the resistivity of a material $\rho = 7.4 \times 10^{-7}$ $\Omega\cdot$m and I want to compute its conductivity $\sigma = 1/\rho$.
Straight forward calculation gives (up to 3 decimals) $\sigma =...
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Definition of Uncertainty
I have some confusion regarding Measurement Uncertainty. In some books/articles it is defined wrt true value as "Uncertainty in the average of measurements is the range in which true value is ...
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How could one measure the capacity of a battery with one instantaneous meter reading?
My car battery when fully charged operated the car lights and air conditioning for a few minutes (without the engine being on) before it was not powerful enough to operate the starter motor.
The ...
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Contact Angle acid-base approach negative square root
I've collected Contact Angles for 3 different liquids (ethylene glycol, glycerol, and water) on a substrate. My aim is to use the acid-base approach (eq. below) to obtain the dispersion, acid, and ...
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Measurement Error Analysis in Gaussian distribution
I am new to statistics and recently learned about ISO guidelines for Accuracy & Precision and Uncertainty & Error. But there are some graphs of probability distribution I found on internet ...
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Why is the Accuracy in the measurement of Time so important in GPS?
I read in a physics book that
Without clocks of extreme accuracy, the Global Positioning System (GPS) that is now vital to worldwide navigation would be useless.
What would be effects on navigation ...
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Least Count Error is Random or Systematic?
There are so many articles on internet on Error analysis in measurement but some of them relate least count error with systematic and other with random error and some associate it with both of them. I ...
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Band structure diagrams
In band structure diagrams, usually we show the dispersion relation between energy $E$ and the wave vector $\textbf{k}$.
Consider the band structure of $\alpha$-Polonium. Shown in the graph below.
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Why do we usually measure liquids and gases by volume?
Why do measure liquids and gases in volume rather than by weight? Isn't that comparatively more inaccurate since volume changes with temperature and pressure?
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How error in a measurement is associated with least count [closed]
Error Analysis :-
Q. I want to know that how error in a measurement is associated with least count of measuring device ?
If I take a measurement with Milimeter scale what the Error I have to assume ...
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How do you measure AC voltage of your mains domestic electricsupply?
If I have a DC voltage source, I can connect a voltmeter across it and get the voltage value. But how do I find out the AC voltage of a voltage source? What will happen if I connect a voltmeter across ...
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How to measure the tension in a guitar string without directly measuring the frequency of the sound?
I'm looking for an accurate method to measure the tension in a guitar string, without using a sonometer setup nor by measuring the frequency.
the current method that I have in mind is to measure the ...
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Is wave function measurable?
I apologize for the length of this naive question. I am not sure it is appropriate for this community.
Is wave function measurable?
This is really a question in Atomic and Molecular Optics.
I hear ...
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Probability distributions of bounded measurement results?
Say that I am measuring a length very inaccurately. For instance, I might measure $1m$ with an uncertainty of $50cm$. If I model the probability distribution as a Gaussian with $\sigma=50cm$, I run ...
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How can be combined the CPM readings from two Geiger counters?
I have two identical Geiger counters, they are very close each other, they are turned on at the same time and turned off after one day.
The display of the first one shows $N_1$ CPM, the second one ...
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Is the magnitude of a vector equal to its length
Suppose a body has a velocity $V =2\hat i$ metres per second. The magnitude of velocity is 2 meters per second . We can draw a vector of length 2 cm to represent this velocity.
According to the below ...
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Why gold is always measured with a balance and not with a scale? [closed]
Why when trading gold apart of purity measurement its mass is always measured worldwide with a balance and not a scale?
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Error analysis via two different methods
We have a quantity $a$ expressed in terms of two quantities $b $ and $c$ as $a = b/c$.
It seems to me that there are two ways of estimating the error on $a$, the "physics" ...
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What does frequency stability of an harmonic oscillator mean?
I don't understand the term in a paper which says that quality factor $Q$ is the inverse of the damping and indicates how sharp the resonance in frequency is. So they use the $Q$ as a proxy metric for ...
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Calculating measured intensity of a Gaussian beam
Consider a light source which emits a Gaussian beam with total power $P_0$, initial width $d$, and divergence half-angle $\theta$ (in radians). The beam radius, measured from the waist of the beam, ...
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How to characterize the accuracy of a tensor value determined experimentally?
How to characterize the accuracy of a tensor value determined experimentally? I'm particularly interested in first and second rank tensor values.
For a first-rank tensor (a vector), measurements are ...
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Isn't defining the unit of length in terms of the speed of light kind of faulty? [closed]
well I was reading Halliday and it defined the standard of length as follows
"The standard of length, which corresponds to exactly 1.0 meters, is the distance travelled by light in a vacuum ...
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How can you measure the propagation distance of a wave?
Suppose a simple spherically-symmetric cosine wave of wavelength $\lambda$ and velocity $c$ is transmitted from an unknown point outwards in $2D$ (in circles). We'll denote this unknown point as $(0,0)...
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What's an inexpensive way to measure the amount of UV light (or IR light) given off by a light bulb? [closed]
What's an inexpensive way to measure the amount of UV light (or IR light) given off by a light bulb? Specifically, the amount at various wavelengths of UV (and IR)?
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Quantum Measurements : Is there a mistake in Eq.91 where independence of wiener process is removed
Here, by introducing inefficient measurement the Weiner process independency for each channels has been removed. It is clear when going From Eq.90 to Eq.91. But again in the measurement record which ...
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What would the measurement device show me if I measured the dye concentration at the pipe location where all of the mass is concentrated at?
I was studying the methods for solving the diffusion equation. Here I found an example problem with the Dirac delta distribution initial condition and zero boundary conditions (example $9.5.1$):
$$ {\...
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Are all operators in Quantum Mechanics both Hermitian and Unitary?
I am trying to understand the basics of quantum mechanics and I am having some issues in understanding the main mathematical properties of quantum operators. In particular, it's clear to me that:
...
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