Questions tagged [measurements]

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15
votes
6answers
696 views

What is the most precise physical measurement ever measured?

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\...
9
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5answers
3k views

Has the speed of light ever been measured in vacuum?

According to: https://en.wikipedia.org/wiki/Cosmic_microwave_background the CMB (Cosmic Microwave Background) "is faint cosmic background radiation filling all space" Also, https://en.wikipedia.org/...
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0answers
32 views

Does all measured quantities by Hamiltonian operator should be real valued? [duplicate]

am not familiar with QM , and i have checked web many times to know wether all measured Quantities of any arbitray system should be real since it is Hermitian ?
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0answers
13 views

How to draw a vernier scale of given details? [on hold]

RF(Representative Frequency)=1/40 to read 1/2 m and 1/30 m and to measure upto 6 m. Mark lengths of 3*(23/30) and 1*(26/30) on the scale.
0
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0answers
27 views

Most efficient method of measuring rate of flow

I understand that devices like venturi meters can be used to measure the rate of flow of a fluid in a closed pipe. There are also devices like the flow meters. But, which one gives a more accurate ...
0
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2answers
26 views

What does it means to increase the accuracy of a screw gauge? And if so how to increase it?

This question is related to the following question from NCERT: A screw gauge has a pitch of 1.0 mm and 200 divisions on the circular scale. Do you think it is possible to increase the accuracy of ...
1
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3answers
56 views

How can multimeter measure frequency with only one wire connected?

Many multimeters have the ability to measure Frequency along with AC Voltage, DC Voltage, Capacitance, Resistance ... But how do they measure Frequency? In my country, $50\ \text{Hz}$ is used as AC ...
2
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0answers
27 views

Different Quantum Measurements

What is the difference between an interaction-free measurement, a weak measurement and a counterfactual measurement in quantum mechanics?
-1
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1answer
29 views

Adding or subtracting mean absolute error

In an experiment to find the length of a rod, n observations were made. ${a_1,\;a_2,\;.\;.\;.\;a_n}$. The mean (${a_{mean}}$) of those observations will give a value very close to the true length of ...
0
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1answer
22 views

Measuring small changes in length using the micrometer screw gauge

Which of the following method/instrument cannot be used to measure small changes of the order of a millimeter occurring in a length of about 50cm. 1)spherometer 2)travelling microscope 3)meter ...
0
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1answer
18 views

Error in Vernier Scale

If a Vernier calliper was made with 1 main scale division equal to 1 vernier scale division could it be even used for measuring ?
1
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2answers
82 views

How Do Scientists Measure Subatomic Particles? [closed]

I'm asking for a list of experiments, machinery, technology and techniques. The only measuring device I really know of is the Stern-Gerlach contraption. Google hasn't been helpful (it only gives me ...
0
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0answers
30 views

Uncertainty in length measurement

I am trying to measure the length and the uncertainty in length of a fiber optic cable for measuring the speed of light. So far, I have measured it the standard way: Using a standard meter scale. I ...
2
votes
2answers
155 views

How do we determine that an object is neutral?

This has been bothering me for a while. Imagine that you are an experimentalist who does not have any known mass or charge to compare against. Imagine also that you do not have any idea about the ...
0
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0answers
9 views

How certain we are that two signals (μ1, σ1) and (μ2, σ2) are distinct?

Suppose we have N1 measurements of first signal and N2 of second. Both are normally distributed with (μ1, σ1) and (μ2, σ2) respectively. How certain we are that these signals are distinct?
0
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1answer
44 views

How to differentiate between quantum states based on phase

Imagine you have a source of photons and a single-photon detector. The source emits photons that can be in any of the following four states: $ |1\rangle $, or $ -|1\rangle $, or $ i|1\rangle $, or $ -...
0
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0answers
44 views

How to measure force required to separate Lego bricks?

I figure clamping each piece is the best way: one to an unmoving plate and the other to a force gauge. But I don't want to spend hundreds of dollars on a digital force gauge, and I'm not having any ...
2
votes
0answers
197 views

Is this analysis contradictory with the $2$'nd measurment?

Summary and Motivation "The below idea is about making a mathematical statement on system $2$ which induces a measurement on system $1$ while $1+2$ obeys unitary evolution." Basically, I'm modelling ...
1
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0answers
36 views

Is there a way to argue that the appearance of the dependence of past states is stochastic behavior?

Suppose in a particular set of observations that you observe what appears to be a correlation of future results based on past results. Is there a way to be certain that such a phenomena isn't just the ...
0
votes
1answer
32 views

Special Relativity - events and measurements

I'm trying to re-ask the Q based on the feedback I got on this forum. Here is the premise for the Q. Consider an IRF, S. Assume only 2-D i.e (x,t). And the observer, O, is as assumed typically "...
2
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1answer
29 views

If the only two empirical measurements we can make are change in length and passage of time, how are dimensions and units of quantities formulated?

So this is something really confusing to me. Recently a professor of mine gave a talk and said something that I thought was very interesting and kind of crazy. "The only two quantitative measurements ...
4
votes
1answer
219 views

Energy cost of the measurement without perturbing the system?

Background Let's say I have a Hamiltonian $\hat H$ (assume the Schrodinger equation) and it be in an arbitrary eigen-energy state: $$ \hat H_{\text{system}} | m \rangle = E_m |m \rangle$$ And I ...
0
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0answers
24 views

Why doesn't a lock-in measure the full voltage from a function generator? (3$omega$ setup)

I'm trying to build a setup for the 3$\omega$ technique, and the equipment is making my brain hurt. When I send a signal directly from the function generator to the lock-in, it only measures about 71% ...
0
votes
1answer
48 views

How do you measure voltage from first principles? [closed]

I've always wondered if you were thrown back in time with just my cell phone, how could I charge it... I know how to make electricity, but how do I check the voltage if all I have access to is, shall ...
0
votes
1answer
26 views

Uncertainty Decomposition in velocity signal

I have a timeseries with repeated measured velocity signal (almost periodic signal). To find the mean time-varying velocity, I have decomposed the signal and computed the ensemble-average and the RMSE ...
0
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0answers
22 views

SI redefinition of the kilogram - what is one measuring? [duplicate]

I have been reading about the new SI units and specifically, want to get a better understanding of the definition of a kilogram. It was written that the kilogram will be defined in terms of Planck's ...
2
votes
1answer
74 views

How does weak measurement affect quantum state?

I'm trying to understand how to describe the quantum state after weak measurement using these two toy examples. Hopefully, these simple examples and your answer will help others who want to learn ...
1
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0answers
34 views

How to measure a Bell inequality violation in IBM Q? (Or analytically)

I made some circuit to prepare a 2 qubit state, but I am having trouble understanding how to measure Bell's inequality. I know the inequality is of the form $$|E(a,b)-E(a,b')+E(a',b)+E(a',b')| \leq 2$...
0
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1answer
46 views

Question on finding the relative error

The question is as under: Find the relative error in Z if Z= A/B Z= A(B^-1) Relative error in A is ΔA/A and in B is ΔB/B My solutions are : As A and B are being ...
2
votes
1answer
38 views

What is the meaning of true value and uncertainty from a measurement?

I am taking the following example: Lengths of an object are measured as : 5cm , 5.2cm , 5.1cm , 5.5 cm. Calculate the true value and the error . The answer is True value = 5.2 cm error = 0.15 ...
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2answers
74 views

Measuring the Thickness of a Paper

I'm supposed to come up with a way to measure the thickness of paper. I've come up with the following approach. Let us suppose we have a paper of thickness $?$, length $a$, breadth $b$, density $\rho$...
-1
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2answers
65 views

Question on Time Interval [closed]

The question states The mean life of an elementary particle pion is $2×10^{-7}$ nanoseconds. The age of the universe is about $4×10{^9}$ years. Identify the time interval that is approximately half ...
0
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1answer
21 views

Calculating percentage error with significant figures

I have a problem with significant figures. In an assignment, the paper gives us data to $3$ significant figures to calculate some values but afterwards requires us to calculate the percentage ...
0
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0answers
16 views

Effect of variation in day length on timekeeping

I was reading about atomic clocks when I came to know that precise measurements of time have shown that the time for earth's rotation is slightly more that 24 hrs (on the order of 10^-3). I was ...
1
vote
0answers
15 views

How to Measure Electric-Field Probe Sensitivity?

I am doing some reading on current methods for detecting electric fields. A figure of merit for the systems is, naturally, the minimum strength of field that can be measured, in units of Volts per ...
-1
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1answer
148 views

What is the difference between resolution and least count of a measurement? [closed]

1.What is the difference between resolution and least count of a measurement? In my physics book the statement of a question is as under : " The time taken by a pendulum for 100 oscillations is ...
1
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0answers
29 views

Uncertanty in Chi-squared measurements, spectra-like

Let's say I have some observational data. For example: in a certain wavelength interval I measure the flux, 10 000 points, and I have the uncertainty for each one of them. For example: ...
0
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0answers
40 views

Can we describe the process of measurement in functional form?

The question was can we describe the process of measurement in functional form? We know hermitian operator can be used to represent measurement. In Heisenberg's picture, it even described the "motion"...
0
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1answer
86 views

Finding the range of time scales by dividing length scales by speed of light

My book states : The scope of physics is truly vast. At one end, it studies phenomena at the very small scale of length (10^-14 m or even less) involving electrons, protons, etc.; at the other ...
1
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0answers
36 views

Subtractive cancellation errors in the lab

I am quite familiar with the problem associated with loss of significance in numerical analysis. This problem seems to be an even bigger problem in the science lab, where subtracting one physical ...
1
vote
1answer
80 views

Is it true that in practice quantum fields are *always* measured by means of coupling to particle detectors?

I'm watching some lectures on Relativistic Quantum Information and in one of them - available here - the instructor is talking about measuring quantum fields. He then says basically that in real ...
0
votes
1answer
58 views

Why do many phones have very different specific absorption rate (SAR) values for head and body? [closed]

I'm deciding on which mobile phone to buy, and since we don't really know if electromagnetic radiation does or does not have adverse health effects (I'm considering cancer and fertility), I'd rather ...
1
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2answers
140 views

A theoretical limit of accuracy?

Is there an agreed upon/conjectured theoretical limit to our ability to resolve the accuracy of time?
2
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0answers
27 views

Would the voltmeters give different readings in a circuit with induced current?

$\def\vE{{\vec{E}}}$ $\def\vD{{\vec{D}}}$ $\def\vB{{\vec{B}}}$ $\def\vJ{{\vec{J}}}$ $\def\vr{{\vec{r}}}$ $\def\vA{{\vec{A}}}$ $\def\vH{{\vec{H}}}$ $\def\ddt{\frac{d}{dt}}$ $\def\rot{\operatorname{rot}}...
0
votes
1answer
151 views

Least count of Vernier

Is least count not always 1 main scale divsion-1vernier scale divsion or is it always least reading possible on main scale/ no of vernier divsions. question: 1 main scale reading be 1 mm Lets say 5 ...
0
votes
1answer
26 views

The difference in using a predetermined error or standard deviation for calculations

Please edit the thread's tags and content if there are mistakes. I am not sure where If I'm posting my question with the right tags. This is a simple question regarding the study of Linear Motion by ...
0
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0answers
68 views

Spacetime curvature and measurements

From a programming perspective, I've always thought of gravitational influence as a kind of vector field, (crudely drawn) which seems to attribute to the motions of bodies through the field ...
2
votes
1answer
73 views

Are there ways to detect/measure photons that don't involve electrons?

As per question, are there ways to detect photons, and/or to measure their energy, that don't involve any interaction with electrons? And if yes, are there detectors which use photon interactions with ...
0
votes
1answer
34 views

Convert negative parameters of Altitude Height into possitive using BMP180 Sensor

I am using BMP180 I2C sensor interface with Arduino and with the help of mentioned below code ...
1
vote
0answers
82 views

How do we quantify and measure the net entropy of today's universe?

We know that the Universe evolved from a very low entropy state in the early universe to very high entropy state of today's universe. What is the quantitative definition of the net entropy of the ...