# Questions tagged [measurements]

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### Measurement coil for magnetic fields, linearity and frequency of the field

I am trying to measure an oscillating magnetic field, of a solenoid and in the air gap of a transformer core. I have a Hall effect sensor, but its frequency range is limited, so I have put together a ...
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### Precision in cosmological constant

The observed cosmological constant, what is its precision? How precise do we know is it not a fluke or misinterpretation of cosmological data?
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### What does “as small as a fraction of an angstrom” mean?

I was reading my school textbook in which the following statement was given: The resolution of such an electron microscope is limited finally by the fact that electrons can also behave as waves! (...
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### Special Theory of Relativuty [duplicate]

I'm trying to learn STR on my own. As I read through a few books and saw a few video lectures - I feel to really understand STR you need to really understand and appreciate precisely (and formally) ...
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### Can we track phonon's path similarly to how we track electron's path in a bubble chamber?

An answer to a recent question argues that Standard Model's particles like electron are "real" because we can see their tracks in e.g. bubble chamber. So now I wonder: can we track quasiparticles ...
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### Tools for measuring vibration/sound of shaking

I would like to know how I can measure the vibration coming from my hand shaking something. My experiment is like this. I put a ball made of strong glass into a closed empty box made of strong glass ...
191 views

### Pure state before and after measurement

Before the measurement of an observable, the quantum state is $$|\Phi\rangle = \sum_i c_i |\psi_i \rangle,$$ with $|\psi_i \rangle$ called "pure states". Once the measurement is done, the quantum ...
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### Measuring the entropy of mixing ideal gases

Suppose I have two compartments of volume V separated by a barrier. Each one has an ideal gas, pure, of N molecules, and with equal pressure and temperature. However, I don't know whether both gases ...
111 views

### Mean velocity in unsteady flow

I'm starting hydraulic experiments, where I'd have to measure velocity in an unsteady flow with a device called Acoustic Doppler Velocimeter (acquisition rate: 100 Hz) . In DSP terms, I'd have a ...
301 views

### Is there a way to measure this observable in QM?

Let a quantum system be described by Hilbert space $\mathscr{H}$ and let $|\psi\rangle$ be an arbitrary state. Define the operator $$P=|\psi\rangle\langle \psi|$$ This is hermitian. It has two ...
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### Best ways to record data on interference pattern using Tektronix DPO 5204B oscilloscope?

I am looking at an interference pattern signal using a Tektronix DPO 5204B oscilloscope which has windows 7 and TekScope software. This interference pattern grows and shrinks with time (approximately ...
104 views

### How to physically make sense of these generalized measurements?

In Quantum Mechanics one often by postulate has that the system is described by a Hilbert space $\mathscr{H}$ and observables are described by hermitian operators $A\in \mathfrak{A}(\mathscr{H})$ on ...
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### Ultra low level light detection: What measurement principles are used?

I was reading up on how Avalanche Photodiodes(APD) are used to detect very low light levels, some are even used in "photon-counting" experiments (in Geiger mode). However, a survey of some commercial ...
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### Is it possible to measure the number of spacetime dimensions?

My question is pretty straightforward to be stated but I don't know whether the answer is as easily reported. It is remarkable and very interesting that Physics work in (almost) any number of ...
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### What is the relation between a measurement and an observable?

Observables are represented by Hermitian operators. First of all, it's a little strange (to me) that some measurable physical quantity is represented by a transformation (or linear map), given that I ...