# 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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### Why do many authors introduce absurd precision into "translated" units of measurement? [closed]

This issue often hits me in the eye, although often the original and "translated" units are present in the text (e.g. "this is 10 miles (16km) away"). A recent phrase however left ...
39 views

### Computing the probability of a measurement of energy for a free particle [closed]

$\newcommand{\ket}{\left|#1\right>}$ $\newcommand{\bra}{\left<#1\right|}$ $\newcommand{\braket}{\left< #1 | #2 \right>}$ Problem Consider a free particle, with no spin, in one ...
1k views

### 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 ...
1 vote
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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-...
29 views

### 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 ...
40 views

### 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 ...
28 views

### 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 ...
103 views

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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 ...
941 views

### 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 ...
38 views

### 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 ...
171 views

### 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 ...
1 vote
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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 ...
241 views

### 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 ...
39 views

### 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. ...
145 views

### 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 ...
114 views

### 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 ...
1 vote
78 views

### 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 ...
27 views

### 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 ...
85 views

### 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 ...
185 views

### 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 ...
4k views

### 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" ...
1 vote
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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 ...
432 views

### 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, ...
1 vote
43 views

### 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 ...
140 views

### 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 ...
51 views

### 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)...
1 vote