Questions tagged [measurements]

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1answer
16 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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3answers
722 views

Propagation of uncertainties

I have five values for the volume of sodium hydroxide needed to neutralise a fixed quantity of hydrochloric acid, each trial with an uncertainty of 0.05 mL. If I take the average of these five values, ...
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1answer
43 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
26 views

Significant figures in complex calculations

In my physics book it is written that ' In any involved or complex multi-step calculation, you should retain, in intermediate steps, one digit more than the significant figures and round off to proper ...
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1answer
70 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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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 ...
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1answer
15 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
28 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
20 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
136 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
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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
17 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
113 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
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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3answers
41 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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1answer
57 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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0answers
27 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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1answer
182 views

Decoherence Free Subspaces and how they stay this way, using the Zeno Effect

I am currently reading papers discussing the Zeno Effect, which discuss how measuring a system at high frequencies can almost freeze the state of a system, or keep the system in a specific subspace of ...
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3answers
45 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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1answer
25 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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4answers
152 views

Difference between unpolarized beam and half H+V polarized beam

Let's say that we have got two light beams. Beam A is not polarized at all. Beam B is composed of half H polarized photons + half V polarized photons. Is there any way to measure those two beams in ...
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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
314 views

How does one compute the state of a quantum system following imperfect measurement?

Suppose I have a quantum system $S$ ("system") with Hamiltonian $H_S$ and initial density matrix $\rho_S(0)$. I allow $S$ to interact with another system $P$ ("probe"), which has Hamiltonian $H_P$ and ...
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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
22 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
14 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
46 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
143 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
41 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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2answers
135 views

Probability of Obtaining a Certain Value (normal distribution)

In my textbook it says that the probability of obtaining a value (which its Gauss distribution is known) is simply $$\frac{1}{\sqrt{2\pi }} \cdot e^{\frac{(x_{1}-X)^{2}}{2\sigma ^{2}}} \text{d}x$$ ...
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2answers
2k views

Total and static pressure: which one is measured?

Which pressure is measure using measuring device in a pipe flow. My first intuition that it is the static pressure. This is confirmed by this Wikipedia article (link) The concepts of total ...
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3answers
168 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
56 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 ...
1
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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
54 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
44 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 ...
0
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1answer
37 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
60 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 ...
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1answer
63 views

How to decide the number of significant figures? [closed]

When we do calculations involving significant figures with their uncertainties, Which rule/rules do we use to decide the number of significant figures in the result?
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0answers
14 views

How relative positions of battery and galvanometer affect the sensitivity of a wheatstone bridge?

I know one of the factors that affect the sensitivity of the galvanometer is the relative magnitudes of the resistances in the four arms of the bridge. the bridge is most sensitive when all the four ...
1
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1answer
55 views

How to find the possible measurements of a quantum system? [closed]

A wave function of an infinite square well is given as $$ \psi(x) = \frac{1}{\sqrt{5a}}\sin\left(\frac{\pi x}{a}\right) +\frac{2}{\sqrt{5a}}\sin\left(\frac{3\pi x}{a}\right),\quad x\in[0,a] $$ How do ...
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1answer
6k views

How to calculate uncertainties of a natural exponential function?

(I apologize if this should be posted in mathematics, however I chose to post it here as it's technically about physics) I conducted an experiment in which position of items were shifted on an object,...
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6answers
1k views

What is the most precise physical measurement ever performed?

Obviously some things, such as the speed of light in a vacuum, are defined to be a precise value. The kilogram was recently defined to have a specific value by fixing Plank's constant to $6.62607015\...
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1answer
13 views

How should I calculated a constant based on a set of experimental values?

I was wondering about the following example: suppose I wish to determine the spring constant determined by swinging a mass to it's end. It is given by the following formula: $$T=2\pi \sqrt\frac{M}{k}$...
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0answers
13 views

Measuring inner choke point on non-uniform silica capillary tube

I hope this is an appropriate place to be asking questions like these (google brought me here when I was searching for a solution)! I make an assembly where a small silica capillary tube (OD of 1mm) ...