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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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Continued calibration of atomic clocks

First off I am not well versed in physics, but as I understand things the second is defined by the ceasium fountain clock which is calibrated as follows How was the first atomic clock calibrated?. Now ...
Emma Harris's user avatar
0 votes
1 answer
41 views

Determine thermal emissivity of material

Is there a practical way of determining it without a lab setup? interested in Aluminum alloys ADC-10 and ADC-12
kellogs's user avatar
  • 109
2 votes
1 answer
85 views

What exactly does the quantum mutual information measure? [duplicate]

Quantum mutual information (QMI) is often said to be the quantum mechanical analog of Shannon mutual information (MI). I realize they can be written with the same formula: $$S_x+S_y-S_{xy} \ ,$$ where ...
Mat's user avatar
  • 201
2 votes
0 answers
63 views

Vernier Caliper Measurement [duplicate]

My doubt is regarding the formula for measurement using a vernier caliper. In my class we were taught the following formula: $Reading = MSR + n(LC)$ (p) (here MSR stands for main scale reading and LC ...
entropy's user avatar
  • 72
1 vote
1 answer
31 views

Relationship between density and temperature - How to know the precise temperature at which a bell inside a Galileo Thermometer will sink?

A Galileo Thermometer consists of bells placed inside a tube that's filled with liquid. As the temperature increases, the fluid density decreases. This leads to a decrease in the buoyant force, and ...
jazzblaster's user avatar
14 votes
4 answers
10k views

If gravitation is negligible for small masses, how was Cavendish's experiment successful with balls much smaller than celestial objects?

If gravitation is negligible for small masses, then how was Cavendish's experiment a success since the balls used were very small compared to the sizes of celestial objects?
JAYANT SINGH GBPP's user avatar
2 votes
1 answer
265 views

Are zeros to the right really significant? [duplicate]

In one of YouTube lectures about significant digits I saw this: I was completely shocked. Both scientific notation numbers when converted to integer would represent same quantity of $1200 \text{kg}$ ...
Agnius Vasiliauskas's user avatar
0 votes
1 answer
37 views

Does changing units affect Significant Figures

Does changing the unit of a physical quantity has no influence whatsoever on the number of significant figures? Suppose the mass of a particle is given as 0.060kg 0.060 has 2 significant figures as ...
Vignesh's user avatar
0 votes
2 answers
57 views

States of entangled particles after no/partial/full measurement

I'm getting contradictory information from the internet concerning entangled particles, measurement, and state knowledge that I'm hoping can be cleared up with a simple setup. Say we have a source of ...
user401228's user avatar
0 votes
0 answers
18 views

Why is my pyrgeometer calibrated as if it has $a >1$ emissivity?

I've acquired an SL-510-SS upward-looking pyrgeometer. In the manual it gives the formula for how to compute the downwelling infrared it picks up: Clearly the $k_2$ coefficient is the emissivity of ...
Cloudyman's user avatar
  • 1,225
1 vote
1 answer
62 views

Why is the uncertainty of the Gravitational Constant $G$ many orders of magnitude larger than that of other important fundamental constants?

Why is the numerical range of uncertainty of the Gravitational Constant $G$ many orders of magnitude larger than that of other important fundamental constants? What are the challenges in precise ...
Alex's user avatar
  • 396
1 vote
2 answers
96 views

How were angles measured in ancient times?

What is one degree (angle measurement)? I know that we calculate one second using atomic clock, one kilogram using Planck's constant, one meter using speed of light but how do we define one degree? If ...
Payal Payal's user avatar
2 votes
1 answer
66 views

The Principle of Homogeneity of dimensions states that you can add,subtract quantities with same dimensions but we cannot add a constant with an angle

Both a constant and a plane and solid angle are dimensionless ie they have the same dimensions , so according to principle of homogeneity should you not be able to equate them ? But it would be absurd ...
Aryan's user avatar
  • 23
0 votes
0 answers
39 views

How to measure the vibration of an object on a video shot at high speed camere?

I have a video fragment which I split into frames (pictures). I use them in pairs (1 frame with 2, 2 with 3, etc.) to find shifts on x and y axes (i.e. how much I need to shift 1 frame to make it like ...
tryingmybest's user avatar
1 vote
2 answers
47 views

Vernier Calliper Reading and significant figures

What if in Vernier Calliper the Vernier Scale division (zero mark) coincides with the Main Scale Reading(MSR) will we take 'n' as 0 or 10 in the formula Reading = MSR + LC (Least Count) x n? 1) If we ...
The's user avatar
  • 13
0 votes
1 answer
45 views

How to add and subtract significant figures?

There are actually two ways given to add or subtract significant figures in different books .In books like concepts of Physics by HC Verma it is written that round of the numbers given first and then ...
ARNAV CHADHA's user avatar
0 votes
1 answer
38 views

Planck-scale measurements of sub-light-speed motion

Firstly, I want to make clear that I am not under the impression that the Planck scale represents a 'resolution' of physical reality, though I can understand why this question might make it seem that ...
P...'s user avatar
  • 111
0 votes
1 answer
66 views

Suppose we observe a photon, what can we measure about it?

I guess we can measure spin, momentum, kinetic energy, position, time, wavelength, e.g., (I don't know much about this), are there other properties? How many degrees of freedom are there? Because for ...
Alex's user avatar
  • 125
1 vote
1 answer
54 views

Fundamental and derived physical quantities

I read that fundamental physical quantities are independent of each other but, if we write length = velocity x time, then length depends on the time interval so how come it is independent?
Manish's user avatar
  • 51
-2 votes
2 answers
177 views

How to Measure the depth of a Hole by Dropping a Rock? [closed]

Let's say I have a rock and a stopwatch. I am standing on the edge of a deep hole or canyon, and can see the bottom. How would I go about measuring the depth of the hole?
Arrow's user avatar
  • 101
0 votes
1 answer
43 views

An instrument for sensitive time interval measurements?

I had the idea to do an experiment at home that would let me calculate the air resistance. $F_{net} = m.a = m.g - f_k$ (kinetic friction), in the case of free fall, so I thought I’d drop an object of ...
jazzblaster's user avatar
2 votes
0 answers
56 views

Observing a particle [duplicate]

We say that there is uncertainty in position when we observe a particle. But first i want to know in detail about how do we observe a particles position and momentum. Suppose we know that an electron ...
Physics's user avatar
  • 63
1 vote
1 answer
26 views

Difference between these two equations to calculate uncertainty when multiplying

I have seen these 2 equations for how to calculate the uncertainty when 2 numbers (that have uncertainty) are multiplied. $$(A\pm a)\times(B\pm b)=(A\times B)\pm \left[\left(\frac{a}{A}\cdot100\right)+...
John Hon's user avatar
  • 2,356
2 votes
1 answer
50 views

Conceptual problem with post-measurement density matrix

I'm asked to derive what the density matrix would be after a measure of $|\phi \rangle$ ($\rho \rightarrow \rho'$). At first I thought that, since $\rho$ has an statistical meaning on an ensemble of ...
Akko0907's user avatar
1 vote
0 answers
25 views

Does the mean of multiple measurements of one sensor reduce the sensor error, in the case of a data-logged K-type thermocouple?

I'm doing an experiment to measure steady-state heat transfer conditions. I have a hot plate connected to a power supply which supplies a constant current (~1.880A in this run). It is very precise, ...
Cloudyman's user avatar
  • 1,225
0 votes
1 answer
26 views

Measuring duration of ultra-short laser pulses

I read that the duration of one ultra-short laser pulse in a pulse train can be measured with autocorrelators or more sophisticated methods like Frequency-Resolved Optical Gating (FROG). In principle ...
Ang's user avatar
  • 53
1 vote
1 answer
120 views

How are general quantum correlation functions actually measured?

These days, the majority of work in theoretical particle, condensed matter, and AMO physics is about methods for calculating exotic correlation functions, of the rough form $$G_{ij} \sim \langle \...
knzhou's user avatar
  • 103k
2 votes
0 answers
51 views

Measurement unit of a tensor product combinations of quantum states in Pusey-Barrett-Rudolph (PBR) theorem proof

I'm dealing with the Pusey-Barrett-Rudolph (PBR) theorem proof, in which we are using a basis built of linear combinations with tensor products. I'm trying to figure out whether measuring those linear ...
Wojciech Szyszka's user avatar
2 votes
3 answers
54 views

How do I find the individual relative uncertainties of cubed terms in an equation and use this to find the absolute uncertainty of a value?

I'm currently conducting a physics project for school and I am really stuck on uncertainties. I am trying to calculate the overall uncertainty in Young's Modulus, with the Bending Beam experiment ...
Rose's user avatar
  • 31
12 votes
2 answers
856 views

Loudness unit, as logarithm of mean squared?

I've come across RMS in a variety of fields. I've come across dB units in a variety of fields. Right now I'm looking at an algorithm for determining the perceived loudness of an audio track (EBU R128'...
TrisT's user avatar
  • 273
0 votes
0 answers
18 views

Measuring AC voltage of the saturation photoelectric voltage

im working on an experiment on the photoelectric effect in which i try to calculate the saturation current of different wave-lengths. i do so by calculating the photoelectric Voltage on a resistor and ...
badLabSrudent's user avatar
0 votes
1 answer
35 views

Measuring physical quantities and spatial displacement

Do all measuring tools work by interacting with the physical property of interest and then changing spatially? Can we only quantify physical properties this way? A clock interacts with time and ...
Rob's user avatar
  • 1
0 votes
3 answers
132 views

Entangled particles and the Andromeda paradox experiment

I know there are other questions linking the two subjects. I am not asking about an explanation, rather I am curious whether an experiment would be possible. To explain the experiment let's start with ...
user's user avatar
  • 1,016
0 votes
0 answers
56 views

Could we measure the one-way speed of light with two connected rotating apertures? [duplicate]

Can we measure the one-way speed of light by passing light through angularly shifted apertures in two disks solidly connected and spinning at a known angular velocity? Here is the apparatus I would ...
Hermanek's user avatar
2 votes
1 answer
115 views

Measurement of electrons positions in an orbital, thought experiment

An orbital can hold upto 2 electrons. Let's take 1s orbital of helium. Now, we use probability density to depict where we can find the electrons in the orbital if we make measurements. Since two ...
LuffyYadav's user avatar
27 votes
2 answers
2k views

Why are quantum effects of the apparatus ignored in quantum experiments?

When reading about various quantum experiments the apparatus often includes things like "semitransparent mirrors", "regular mirrors", "polarization filters" and others. ...
Vilx-'s user avatar
  • 3,101
1 vote
0 answers
31 views

How long does quantum Zeno effect last?

Everywhere I read about the quantum Zeno effect, the phrase used is: <"immediately" after the measurement, the system remains in the observed state>. What does "immediately" ...
Abc2000ro's user avatar
  • 431
0 votes
0 answers
39 views

If lidar is used underwater, would passing through a turbulent surface into a pocket of air (e.g. a "moon pool") distort the resultant image at all?

I have zero experience with lidar systems, but I have been under clear water and looked up at the interior/ceiling of an indoor pool, and even the slightest turbulence at the surface distorts what I ...
rccapps's user avatar
1 vote
0 answers
51 views

Measurement of the momentum of electron when the momentum is very small

In particle physics, it is usually no problem to determine the momentum of a charged particle such as electron, by using something like a pixel detector. This relies on ionization. There is also ...
0x11111's user avatar
  • 141
-2 votes
2 answers
91 views

In real life, we can have a pencil of length 2 cm. Can we have pencil of length $\sqrt{2}$ cm? [duplicate]

In real life, we can have a pencil of length 2 cm. Can we have pencil of length $\sqrt{2}$ cm? My answer to that was no , we cannot even make 2 cm pencil. My argument was that when are working ...
user avatar
0 votes
1 answer
46 views

Determine the more accurate way of measuring the angle

I need to measure an acute angle in a right triangle. There are $2$ methods. Use a protractor with precision to $1^\circ$ to measure the angle. The result is $5^\circ$. Use a ruler with precision ...
youthdoo's user avatar
  • 147
4 votes
2 answers
125 views

Temperature estimation based on very quick measurements

I want to preface by saying I'm not a physicist, I'm a hardware designer at an R&D center trying to wrap my head around temperature measurements, so please forgive me if my questions are stupid or ...
Iliyan Antov's user avatar
0 votes
2 answers
112 views

Can measurements in physics fundamentally only yield rational numbers? [duplicate]

I'm currently studying physics and contemplating the nature of measurements. It seems to me that in practical scenarios, measurements are often represented using rational numbers. However, I'm curious ...
bananenheld's user avatar
  • 2,035
0 votes
3 answers
97 views

Question regarding aparent position and velocity of an object

A time lag is always involved while observing objects. Due to this reason we can never observe the correct position of an object at a particular time. We will see it where it was some times ago. Is ...
user avatar
0 votes
1 answer
66 views

How is the interference pattern of the double slit experiment quantitatively measured? [closed]

The single photon / single electron double slit experiment shows particles appearing as dots on the screen. This is explained as being due to the collapse of their wavefunctions. However, if they were ...
Blacklight MG's user avatar
1 vote
2 answers
48 views

Period of the pendulum (realistic) is shortening in time?

I am doing an experiment with a pendulum and am trying to measure its period over time. I built myself a contraption that uses a 3D printed pendulum with a weight attached at the end. For this ...
Patrik Kokinda's user avatar
1 vote
0 answers
49 views

Time evolution of monitored quantum dynamics

Let us assume that the quantum system consists of Hilbert space $H$ with basis vectors $|i\rangle$. The initial state $|\Psi(0)\rangle$ evolves in discrete time steps such that $|\Psi(t+\delta t) \...
Young Kindaichi's user avatar
0 votes
4 answers
83 views

Understanding how to measure angular momentum [closed]

In pure rotation, angular momentum is measured about the rotation axis. This angular momentum is measured with respect to that axis. Why do we consider it universal? It should change with respect to ...
Deepam Saxena's user avatar
0 votes
0 answers
9 views

Measuring Temperature of Water-filled Methacrylate Capsule: Laser Thermometer Accuracy and Penetration Depth Inquiry

Imagine that I have a methacrylate capsule filled with water (8cm in diameter and 30cm in length). If I wanted to measure the temperature with a laser thermometer pointing at the capsule, what ...
Eladio's user avatar
  • 1
1 vote
1 answer
81 views

Measurement of Electric field

I am aiming to measure the strength of an electric field at different positions in space. The electric field is generated by a coil, which is driven by an AC current. This work is based on this paper: ...
Fabian Pfeiffer's user avatar

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