Questions tagged [measurements]

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5answers
3k views

Experimentally measure velocity/momentum of a particle in quantum mechanics

In the context of quantum mechanics one cannot measure the velocity of a particle by measuring its position at two quick instants of time and dividing by the time interval. That is, $$ v = \frac{x_2 - ...
-4
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1answer
76 views

Entanglement as determined correlation

I imagine that at the moment of entanglement the wave function collapses and the quantum states of the 2 entangled particles will be set, so that there will be no superposition after the moment of ...
3
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0answers
60 views

Do imaginary measurements exists? [duplicate]

I'm sorry if this question is too metaphysical, but I will give it a try. My textbook in introductory quantum mechanics is basing a lot of its proof and derivations on the fact that the value of the ...
1
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2answers
50 views

What Sensor Replaces CCD for Measurement of Astetroids in the Near Infrared?

In astronomy, ground-based telescopes use charged-coupled device (CCD) sensors to measure the color of asteroids in the visible wavelength range (see here for example). If I'm not mistaken, CCD ...
0
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1answer
850 views

Why does the scale reading depend on the position of the object on the scale and how to equalize that?

I have a KERN DS 100K0.5 industrial platform scale, range up to 100 kg, resolution 0.5 g, more or less like this: The specifications say reproducibility 0.5 g, linearity 1.5 g. When I stand on the ...
0
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1answer
64 views

How much tritium is there in the Karlsruhe Neutrino Experiment (KATRIN)?

It is a new revolutionary experiment to finally measure the rest mass of the electron neutrino (and thus, combined by other data, may also answer other open questions (is it a majorana particle, ...
1
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1answer
70 views

Uncertainty in the temperature measurement using an oscillator coupled to a bath

I'm considering a harmonic oscillator coupled to a bath (e.g. a gas). The oscillator is subject to a damping and a fluctuating Langevin force $$ m\ddot{x} + m\gamma\dot{x} + kx =F_\mathrm{fluct}, $$ ...
1
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1answer
285 views

What is the cause of shot noise in an optical measurement?

Is it: The statistical variations inherent due to the discrete nature of the photon? The statistical variations inherent due to the discrete nature of the electron? The randomness caused by the photon ...
0
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0answers
135 views

Verify standard deviation of position samples with reference

Given are the reference data samples of a moving object and data samples that are obtained from a radar sensor with corresponding standard deviations for each sample point $\sigma_t$. I would like to ...
0
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1answer
306 views

How can you measure capacitance/inductance without an oscilloscope?

Since we know what the current/voltage output of a RLC circuit is as a function of $R,L,C$ hooking up an $RLC$ circuit is one way to determine an unknown capacitance or inductance? How did people ...
3
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1answer
230 views

Does a precise definition of the meter not involving light exist, so that variation of $c$ can be tested?

The second is defined as the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. The metre ...
1
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1answer
265 views

Uncertainties of coefficients in linear fit [closed]

I'm trying to calculate the uncertainty of the coefficients in a linear fit, but I'm not sure how to do it. on the one hand, I can extract the error with matlab statistical tools but on the other hand ...
4
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1answer
72 views

Diffractionless optical systems

Conventional optical systems are (at best) diffraction limited. But as I understand it, that is solely due to the instrument altering the properties of the incoming radiation -- e.g., an Airy disc ...
3
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2answers
161 views

What does $14.2 \pm 0.1$ mean?

I need to experimentally determine some value $Z = 3X+Y$ where $X$ and $Y$ are measurements. I was given the value for $X$, let's say $X = 14.2\pm 0.1$. Up to now I thought that if I read something ...
1
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4answers
76 views

Thermodynamics Question: Does measuring the temperature of an object change its temperature?

Suppose that I want to measure the temperature of an object, such as a pot of hot water. When I stick the thermometer into the pot, I know that the temperature measured by the thermometer is its own ...
2
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0answers
413 views

Measuring Stiffness & Spring Damping Coefficient of Hard Rigid Material Objects

I have a set of objects made out of mostly stiff materials and what I want to do is to find out the stiffness and spring damping coefficients of those objects. I need to find out the values ...
1
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1answer
466 views

Rigorous error analysis theory

Now that I finished my pregraduate laboratory courses I've been thinking a lot about the error theory we used for our measurements. I tried to find a mathematically rigorous book on error analysis but ...
0
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1answer
76 views

What is the typical measurement error in EDX peak location?

In EDX, peak locations (kV values) give information about elemental composition of a sample. How accurate is the position of those peaks? For example, could Pd ($L_{\alpha}$ 2.838 kV) possible show ...
6
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1answer
566 views

How do we actually measure the temperature of a BEC?

I guess quite some people here are familiar with Bose-Einstein condensates (BEC) and their properties. We know that the necessary temperature for condensation is given by $$ T_C \simeq 3.3125 \frac{\...
-1
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2answers
537 views

Does the state of a quantum system change between measurements?

I've recently started studying QM and I was told that the quantum state in which a particle is will change as its wave function evolves. So let us say I have a source that emits one photon at a time. ...
2
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0answers
96 views

Anomalous oxygen in aluminium sample SEM EDS

I have a sample of aluminium which I'm interested in finding the rough composition of. The sample is a part of a large number of samples which I sanded down and polished with a polishing table. I ...
1
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1answer
593 views

Can smartphones detect both AC and DC magnetic fields?

I'm trying to locate good areas in my house to store magnetic media that is sensitive to magnetic fields. I found a spot that's ideal, but it's located about 18" from two electrical devices: a ...
2
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1answer
222 views

How are changes in density of matter as universe expands measured?

In this answer John Rennie says about deciding whether something observed by astronomers is matter: ... when we say matter we means anything that scales like matter as the universe expands. This ...
3
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1answer
162 views

Is there a low-bugdet method to measure micronewtons?

I will have to measure very small EM forces (on the order of 10^-6...10^-5 Newtons) acting on a small copper sphere or plate (of about 0.05 kg). I could hang the copper object with a long thread and ...
7
votes
1answer
457 views

Why can “Magnet-O-Meter” phone app detect magnetic objects that are not magnets?

I downloaded the "Magnet-O-Meter" Android app, that allows access to the device's magnetic field sensor. I see the measurement go up when I bring my phone near a magnet, which is to be expected, but I ...
1
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1answer
76 views

Standing Wave with an Unexpected Pressure Field

Recently, I have tried to measure pressure in a '' Standing Wave (SW)'' field established in air using a 1/8'' traversing microphone (B&K). The ''SW'' field (at 60kHz) is produced using a ...
0
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1answer
56 views

Using photometric quantities for determination of intensity of laser light

I would like to measure the intensity of a laser beam after it has passed through a translucent material. However, the sensor that I am using returns values in lux, which reflects the subjective ...
1
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0answers
171 views

Is the coincidence between these large numbers purely accidental?

Following are 3 sets of some very interesting data: Size of proton- $10^{-15}$m Size of observable universe- $10^{26}$ m Mass of an electron- $10^{-30}$ kg Mass of observable universe- $10^{55}$kg ...
5
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2answers
535 views

How to estimate the uncertainties in measurement that can be used in the “adding in quadrature” method?

For examples, if I measure length with a meter stick with the smallest unit of 1mm, can I use the uncertainty of 0.5mm in this formula: $$\Delta C = \sqrt{\left(\frac{\partial C}{\partial x_1}\Delta ...
1
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1answer
43 views

Covariance when two parameters have relative scaling error

I was reading error propagation from "Introduction to Statistics and Data Analysis for Physicists" by G. Bohm and G. Zech, and I stumbled upon this example, Given are the sides a, b with a reading ...
1
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2answers
109 views

Is the average of acceleration magnitude valid?

I am doing two tasks of flipping card and lifting a load. I am collecting data for this two tasks for a week. I want to find the mean acceleration for each day. As it is 3-axis I thought it is good to ...
4
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1answer
343 views

How to measure gravitational acceleration in airplane?

I want to see (actually: show to my kids) evidence of the $1/r^2$-decay of gravitational acceleration by measurement, in a way as simple as possible. So I was thinking of measuring gravitational ...
10
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2answers
1k views

Different precision for masses of moon and earth online

The Google search page for "mass of moon" shows a value with nine significant digits of precision. The corresponding page for "mass of earth" shows a value with only four significant digits. (The ...
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2answers
95 views

How would someone determine the speed of sound in water experimentally?

I'm in highschool so I'm looking for a highschool-level lab idea.
0
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1answer
18 views

how to understand sensitivity of a system

I am reading a book about measurement. It introduces a concept of sensitivity of the system: the output of the system when the input undergoes a small change. Assuming the system can be described with ...
1
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4answers
222 views

Measuring very small temperature differences

Can one use a thermometer with $\pm$5 mK accuracy to measure a temperature difference of 2 mK (the measurement is near 100 mK temperature on a sample on an ADR)? Using the same thermometer, I am ...
2
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2answers
43 views

Replacing '< x' by a defined value [closed]

I do have a dataset containing nearly a decade of particulate matter measurements. At the lower precision limit of the measuring instrument, there are values given like ...
31
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3answers
1k views

Why does interaction with a Stern-Gerlach machine, or any other laboratory apparatus, not cause a measurement?

Consider a Stern-Gerlach machine that measures the $z$-component of the spin of an electron. Suppose our electron's initial state is an equal superposition of $$|\text{spin up}, \text{going right} \...
1
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2answers
87 views

Is measurement of coordinates possible near strong gravity?

We know that Schwarzchild metric describes an asymptotically flat spacetime. This means that far away from the event horizon we can safely interpret the $r$ coordinate as distance from the center. ...
0
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1answer
39 views

Handling systematic error that varies between measurements

I have a block of glass. The glass is tilted at some angle $\alpha$ with respect to a fixed axis. I rotate the glass and $\alpha$ changes. The way I am rotating the glass is by placing it onto a stick ...
3
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3answers
240 views

Measurement and transition rates

We can use time dependant perturbation theory (specifically Fermi's Golden Rule) to calculate the transition rate (probability of transition per unit time) from one energy eigenstate to another. ...
0
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1answer
683 views

Precision and Accuracy course review [closed]

In the following course review question I need to choose all the answers that are true about precision and accuracy 1)Definitions of accuracy and precision depend on the type of measurement you are ...
3
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1answer
155 views

A question about error analysis, please help?

So in class we are doing an experiment on the period of a pendulum where you measure the period of oscillation with a stopwatch. Now the way the lab manual shows how to do the error analysis is by ...
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0answers
74 views

Non-linear bell's inequality?

Consider the Bell setting, where Alice and Bob get inputs $x,y$ and they perform measurements $\{M^x_a\}_a,\{N^y_b\}_b$ respectively on their shared pure state $\Psi_{AB}$ to obtain outputs $a,b$. ...
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3answers
480 views

What is precision?

I’ve learnt that accuracy is how close to the true value a measurement is (i.e. low discrepancy between the experimental and theoretical values). Precision, on the other hand, is the reproducibility ...
2
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0answers
220 views

How can we measure light quality, quantity and duration in the field?

I am interested in measuring the light availability for coffee plants under a range of different adaptation practices (shade, cover crops etc). We want to ensure that the measurement can be automated (...
1
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3answers
60 views

When analyzing data from an experiment, is each $x_i$ a random variable?

When we perform one experiment we have to measure several quantities and take some number of measurements for each of them. Those quantities can be things like positions, instants of time, and so ...
3
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1answer
280 views

Why do we divide the standard deviation by $\sqrt{n}$? [duplicate]

I've been studying experimental physics on the book "The art of experimental physics" and on the chapter about error analysis there's something that has been bothering me. The author says: Now that ...
0
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4answers
4k views

How to measure the inner diameter of thin tube (0.5mm to 2mm)

Does anybody know what method or equipment could be used to measure the inner diameter of capillary tubes? They would be in the region of 0.5-2mm in diameter. Edit: the tube is made of plastic and I ...
0
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1answer
697 views

Problems measuring viscosity of water with a Falling Ball Viscometer

I am measuring the viscosity in water using a falling ball viscometer. In my system, I believe that exists two forces: The force difference between the weight and buoyancy of the sphere: $F_g = m'g =...