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# Questions tagged [measurements]

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### How to measure the mass and balance point of a human forearm?

I've been trying to find this out for about a month now. I'm usually met with humorous but not really helpful comments about chopping my own arm off. I'm preferably looking to do this on a budget ...
488 views

### Is there an official list of independent units of measurements?

When I say 'independent units', I mean those which cannot be broken down anymore, and simultaneously forms the basis for any more, complex measurements. For example, height, length, and width can all ...
143 views

### Is there a way to measure the thickness of a metallic plate of order of micrometers?

I have a $5 cm×5 cm×? \mu m$ copper plate. Where '$?$', the thickness of the plate, is really small (about 30um). Is there anyway using physics to calculate the thickness? Update: Sorry I forgot ...
13k views

### How do laser “tape measures” work?

There is a device available for about $\$40$, which fits in the palm of the hand, runs on two AA batteries, and can measure distances up to$50\,{\rm ft}$to an accuracy of$\sim \frac{1}{8}''$($\sim ...
68 views

### making sense of measures in electronics

I am in secondary school in the UK, and at this point in physics the information we are given is very vague at a fundamental level. My main concern is with electricity and circuits, and the measures ...
164 views

### Is wavefunction collapse “global”?

I have the feeling that the premises of this question may not be coherent (so to speak), but here goes: Suppose we have a system $X$ in a quantum superposition between states $0$ and $1$, say, with ...
1k views

### Estimate heating wires temperature

Im design a power supply to work with heating wires and one of the task is to estimate the temperature of the bare wire for a given current or power consumption. I've tried to measure the temperature ...
88 views

### Measurements in quantum mechanics

Why does measurement change things? I read that measurement changes things because we have to bounce photons off an object to 'see' it and that changes its position, momentum etc... But on the other ...
172 views

### Why doesn't precessing a spin cause a measurement?

When an electron is placed in a magnetic field, its spin precesses. Why doesn't this reveal the spin via angular momentum being transferred into the environment? Impractical Thought Experiment ...
1k views

### How precise can current technologies measure the mass of an object?

Masses of various objects are listed on this wikipedia page: Orders of magnitude (mass). For example, mass of an HIV-1 virus is on the order of 1 femtogram. Are these data actually measured (which I ...
34 views

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### Radius of $n^\rm{th}$ orbit of an atom in terms of Bohr's Radius

Bohr's Radius$=0.529$ Angstroms My book says that the radius of $nth$ orbit of any atom can be calculated by: $$r=n^2 a_o$$ where $a_o$ is Bohr's Radius. But I think it should be given by following ...
658 views

### How to find the error of all the counts within the Full Width Half Maximum (FWHM)?

We've been doing Gamma ray spectroscopy and have peaks from various sources. We'd use Poisson statistics, but obviously the detector doesn't have a resolution of zero, thus we are summing the counts ...
50 views

### Could neutrinos be used to take high resolution pictures of atomic nuclei?

Of course, this is obviously not feasible with modern technology but is it theoretically possible?
68 views

### Practicality of measuring observables

In quantum mechanics Hermitian operators acting on the Hilbert space of a system are observables. From what I understand this means that there is some measurement we can do such that the eigenvalues ...
377 views

### How well can we localize gravitational wave sources?

A recent question cited a story about the recent gravitational wave detection saying that we can use the gravitational wave sensing to find supernova earlier in their process of collapse: [with the ...
1k views

### How to (safely) measure the surface area of a human body? [closed]

Here's a question just for curiosity. You measure mass on scales. You could measure volume by submerging in a bath with a snorkel system. But how could you measure a living human's surface area ...
69 views

### How could the BOE (barrel of oil equivalent) be measured?

The barrel of oil equivalent was given as an example of gigajoule scale energy. "The barrel of oil equivalent (BOE) is a unit of energy based on the approximate energy released by burning one barrel (...
986 views

### Calculate how many photons hitting a sample that are absorbed

In the determination of the quantum yield of a photoisomerization, $\Phi,$ the following is needed $$\Phi = \frac{\mbox{Number of "reactions"}}{\mbox{Number of absorbed photons}}$$ The photon flux ...
239 views

### Venturi “Turn Down” [closed]

I'm sorry if this isn't the right forum for this question, but physics is the only stackexchange which had many results for Venturi. I'm trying to measure the flow of air through a 16mm hose/pipe ...
62 views

### Is there any well-defined, measurable atomic size?

Is there any well-defined, measurable size at the atomic scale? I was under the impression that the van der Waals radius was a good way of describing the size of an atom, but it turns out to be a ...
1k views

### Is there a tool to measure the chemical potential of a system?

Let's suppose I put you inside a room filled with a gas. You can measure its pressure directly with a barometer. You can measure its temperature directly with a thermometer. Can you measure its ...
I've found several sources that say the van der Waals radius of hydrogen is $120 pm$. How precisely do we know this number? What order of magnitude is the error on this measurement?