What is Measuerment: Definition and 31 Discussions

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1. Significant figures doubt

(i) and (ii) makes sense to me but the answer key says (iv) is correct too, but shouldn't the answer be 2 significant figures for (iv). 2 and the first zero are significant if the lc is 100 kg as far as I understand
2. I Measurement of heat as an interval measurement or a ratio measurement

Hello! I am new to this forum and I'm not even sure if this is the right place to ask but here goes: I am studying Research Methods. I got to the part where the teacher is teaching us about levels of measurement. They said that there are a few levels but the two that are significant to my...
3. I 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 sphere. The diagram below illustrates the type of sphere I am looking for [1]. Two ports are...
4. I Measuring reflectance of a non-planar object w/ an integrating sphere

I am designing an experiment to measure the reflectance (diffuse+specular) of insect specimens, and I plan to use an integrating sphere to collect the measurements. Typically, I have seen that reflectance measurements with integrating spheres are done with planar (i.e. flat) sample objects. So...
5. Engineering How to calculate the interference voltage?

Hello everyone, I have this circuit and I need to determine the interference voltage. I am not sure, where the interference voltage is applied and how to determine it. I think the interference voltage is uv nad my equivalent circuit looks like this: Am I in heading into the right direction...
6. Least count error Vs Least count

I know that least count is the smallest measurement that is possible with a measuring device. But I fail to understand the exact meaning of least count error. According to my textbook, the following is the definition of least count error. "Least count error is the error associated with the...
7. Finding number of significant figures

I am using these rules to determine number of significant digits. (1) All trailing zeros following decimal are significant (2) All trailing zeros in a number without decimal point are not significant (3) All non-zero digits are significant It seems rule 2 will not apply here and therefore number...
8. I Why Can We Use This Mathematical Formula for Mean Value of Measurement?

Hi, I'm new to the quantum world, and would like to know why mathematically can we say that for mean value of measurment: <T>=<phi|T|phi> ?
9. I Measurement of a qubit in the computational basis - Phase estimation

Hello, I have a question about the measurement of a qubit in the computational basis. I would like to first state what I know so far and then ask my actual question at the end.What I know: Let's say we have a qubit in the general state of ##|\psi\rangle = \alpha|0\rangle + \beta|1\rangle##. Now...
10. A Thought experiment in relativistic quantum mechanics?

Background --- Consider the following thought experiment in the setting of relativistic quantum mechanics (not QFT). I have a particle in superposition of the position basis: H | \psi \rangle = E | \psi \rangle Now I suddenly turn on an interaction potential H_{int} localized at r_o =...
11. Asymmetric uncertainty intervals in astrophysical data

My initial guess was to calculate the upper and lower value, and then average those two values, but I don't know whether this is correct to make the uncertainty interval symmetric. After I calculated the average value, I subtracted it form the upper and lower value, and obtained the symmetric...
12. I Did Schrödinger himself take his "Cat Experiment" seriously?

In 1935, Austrian physicist Erwin Schrödinger was looking at a concept called a "superposition." Superposition is when two waves meet and overlap and interact, which can lead to different results based on the circumstances. The concept can be seen in the regular-sized world as well, in...
13. I Applying an observable operator on the current state

hey :) assume I have an operator A with |ai> eigenstates and matching ai eigenvalues, and assume my system is in state |Ψ> = Σci|ai> I know that applying the measurement that corresponds to A will collapse the system into one of the |ai>'s with probability |<Ψ|ai>|2. with that being...
14. B Trivial questions regarding parallax and measurement of distances.

While trying to understand parallax and its use in measuring distances here, I had a few questions. (1) Parallax is defined as the apparent movement of an object with reference to another object in the background when one views it from different angles. As in the movement of a finger relative...
15. I Frauchiger & Renner: There's a Mistake, Right?

Hey there! I was recently pointed to this thought experiment, claiming an apparent 'contradiction' involving the various predictions of the observers. Now, this has been discussed on PF quite recently, but I found the discussion rather hard to follow. I've read the paper, the PF discussion...
16. B Measuring Objects using Dissimilar Units

Quantumly speaking: Can speed be measured? If so, why? If not why? This is a serious question. Speed involves a distance unit and a time unit. For example .. "ft/sec" .. and it is illogical to divide seconds into feet. Having made this point can speed be quantumly measured and how do you...
17. I Calculate measurement uncertainty? I made one measurement....

How to calculate measurement uncertainty of m. I understand I should use these formulas to calculate it if I had data of many measurements, but when have only measurement then it becomes undefined, because of 0/0 in standard deviation formula. ##u(m)=\sqrt{u_a^2(m)+u_b^2(m)}##...
18. A Decoherence of measurement outcomes

Suppose we have a quantum system ##Q## with an initial state ##\rho^{(Q)}##. The measurement process will involve two additional quantum systems: an apparatus system ##A## and an environment system ##E##, hence giving the initial state of the system ##\rho^{(AEQ)} = \rho_{0}^{(AE)}\otimes...
19. I Measurement of a particle's position using photons

I've read that a particle's position can be measured by firing a photon at it, but how does one actually determine the position of the particle by doing this? What is the maths behind it (is it calculated from momentum conservation)? Furthermore, I've read that increasing the energy of the...
20. Height of an island beyond the horizon

Homework Statement If I am standing on the ocean shore, and my eye level is 6 feet above sea level, how far above the horizon would an island appear that is 15 miles away and whose highest point is 200 feet above sea level (assuming the earth’s diameter is 3,960 miles?) In other words, how many...
21. D

Help intagrating hertzmeter into analog linear power supply

First off I'm not an engineer nor do I have a electronics background. I have an old Linear (HP 6284A Power Supply). I would like to be able to display Hz/CPS. I need to measure the speed of a tattoo machine. (basically two coils that make and break connection through out its use. From what...
22. A Quantum measurement with incomplete basis?

In page 9 of http://www.theory.caltech.edu/people/preskill/ph229/notes/chap4.pdf we can find simple form of Bell inequalities for three binary variables: $$P(A=B) + P(A=C) + P(B=C) \geq 1$$ which is kind of obvious: "This is satisfied by any probability distribution for the three coins because...
23. How does a 5th wheel contribute to the accuracy of car speedometers?

I'm wondering how does speedometer work. To be specific let's talk about car speedometer. I googled it and found out that there are different kind of speedometers, but not quite understood it's working principle. My question is not about how it shows us speed (Mechanically with arrow or...
24. How to measure output voltage of B200?

Hi, I am a new student and trying to to measure the power and voltage output from B200 SDR device (https://www.ettus.com/content/files/b200-b210_spec_sheet.pdf) using oscilloscope (TDS3000 Series: https://www.atecorp.com/ATECorp/media/pdfs/data-sheets/Tektronix-TDS3000_Series_Manual.pdf)...
25. Calculating voltage which voltmeter is showing

Homework Statement Schematic of circuit is not given, only the text which I translated into English. Using a voltmeter with internal resistance of 6k ohm, voltage between two points, 1 and 2 of a circuit of constant current, is measured to be 8v. Then, using a voltmeter with internal...
26. B What is a good physical reference for microstrain?

I can say that the distance between my knuckle and my finger joint is 1~ inch, that a baseball weighs ~1 lb, and ~60 joules is the feeling of dropping a bowling ball on your foot. I'd like to understand strain in this way, can anyone offer a common place reference? Also, I know strain is...
27. How can I do when I make a Log2 towards zero?

Good day, Homework Statement I want to make a measurement on qubit by using formula von Neumann entropy using Mathematica given as below; Homework Equations (ρ)=−Tr(ρlog2ρ) The Attempt at a Solution The ρ={{0.5,0},{0,0.5}}My problem is, when I make the log2{{0.5,0},{0,0.5}} I get the...
28. Measuring volume: Solid vs Liquid/Gas

I was just curious... what is the practical reason behind having two separate units for measuring volume? For instance, we can use cubic centimeters and mL interchangeably in practical medicine, i.e. injections. But we tend to use cubic (centi)meters for solids, and liters for liquids/gasses...
29. Finding the random uncertainty of a set of values

Ok, for the switch-on voltage of a red LED I have the readings as follows, all in volts: 1.45, 1.46, 1.46, 1.44, 1.45. The mean of these readings, in volts, is 1.45 (I rounded up to 2 decimal places as my scale reading uncertainty was +/-0.01V, and my teacher told me to round them up since to...
30. Spins and Qubits: Exploring Determinism in Measurements

I'm aware that this is a very basic question, yet I hope to get a non-trivial answer :wink: Let's assume to have an apparatus A (to make measurements) that is oriented in space. We first point it along the z axis and measure a spin σz = 1. Then we rotate the apparatus through an angle of ½π...
31. Determination of moment of inertia of a hollow cylinder

Hi! I got the task to determine the moment of inertia of a hollow cylinder, however it's not about just measuring the mass and the inner and outer radius and putting it into the right formula, instead I should roll it down an inclined plane. 1. Homework Statement I'm only allowed to use the...