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Questions tagged [measurements]

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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, ...
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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.
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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 ...
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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 ...
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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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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-...
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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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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 ...
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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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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 ...
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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). ...
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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....
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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 ...
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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 ...
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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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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 ...
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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?
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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 ...
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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 ...
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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: $$ \...
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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 ...
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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 ...
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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 ...