# Tag Info

## Hot answers tagged experimental-physics

60

You are right that, without a force acting on it, water falling from a tap could not follow a spiralled path. The tap, however, creates an illusion - the water appears to be spiralling, but it isn't - it's falling straight down. The illusion is created by the "turbine" inside the nozzle, which rotates the ring of spouts that the water falls through. The ...

14

The resolving power of a prism is given by the formula $$\frac{\lambda}{\Delta \lambda} = b\ \frac{dn}{d\lambda},$$ where $b$ is the base length of the prism, $\lambda$ is the wavelength and $n(\lambda)$ is the refractive index. You don't say, but let's assume you are using a crown glass prism. According to this useful document, crown class has ...

11

Nobody ever tried with LHC, but here is Anatoli Bugorski: http://en.wikipedia.org/wiki/Anatoli_Bugorski Given the damage he received with a beam of 70 GeV protons (intensity ~10^13) you can probably imagine the damage you would receive from 6500 GeV protons (intensity ~10^32). For more info about the "danger" of the LHC beams, I suggest you read about the ...

8

@innisfree's answer covers the tap in question, but I'd like to expand briefly. Like he says in his answer, without a force acting on it, water falling rom a tap could not follow a spiralled path Well, what if you do apply a force? Then yes, you can make water fall in a spiral. This picture is from a video I found while researching Chladni Plates. ...

6

This probably won't work in practice at all. First, there is the problem of Rayleigh instability that splits streams into droplets. It is true, that the more laminar the flow is, the more stable the stream. But in this case, the mechanism in the turbine will disturb the water rather than make it laminar, so the streams won't keep together in nice strings. ...

5

Maybe the most famous example of potential failure of GR are rotation curves of galaxies. However, it could also be explained by additional mass (dark matter), so it's not clear yet how this will be resolved. (A similar situation happend in the early 1900s when people predicted planet Vulcan near Mercury to account for it's perhelion anomaly. We know how ...

5

Evidence that there are distinct protons and neutrons in nuclei starts with the Pauli term (pairing term) in the semiempirical mass formula of the liquid drop model. Furthermore, all nuclei with even numbers of protons and neutrons have nuclear spin of zero. This is consisent with shells being filled with spin up and spin down pairs of nucleons, each pair ...

4

You say: I found out that the speed of light is NOT invariant in an accelerated reference frame but things are more complicated than this. The local speed of light measured by an observer is always equal to $c$, and this remains the case whether the observer is stationary, moving, accelerating or anything else you might think of. So if your Michelson ...

4

"The theory of relativity is considered to be self-consistent, is consistent with many experimental results, and serves as the basis of many successful theories like quantum electrodynamics. Therefore, fundamental criticism (like that of Herbert Dingle, Louis Essen, Petr Beckmann, Maurice Allais and Tom van Flandern) has not been taken seriously by the ...

4

Are there any cosmological observations which general relatively fails to predict? No. One issue with GR is that it admits singularities (e.g., black holes, kugelblitzes, the initial singularity), a feature that most physicists think can't be correct. However, as of this date, there have been zero observations of (for example) interior of a black hole ...

4

The LHC luminosity is $4.6\cdot 10^{32} /cm^2/s$ (reference) - that is an incredibly intense beam, but there is a finite number of protons going around. The thing that really matters though is the number of protons in the beam at one time: there are 2808 bunches in the beam (http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/collisions.htm) with a ...

3

When they need to empty the beam of particles they are directed into a "beam dump" target Absorption Each beam dump absorber consists of a 7m long segmented carbon cylinder of 700mm diameter, contained in a steel cylinder, comprising the dump core (TDE). This is water cooled, and surrounded by about 750 tonnes of concrete and iron shielding. ...

3

I think they just take a large amount of material and look for protons decaying in it. There are a lot of protons, so in order for none of them to decay the half-life must be absurdly long.

3

Project Excalibur The idea of a nuclear pumped X-ray laser was one which was investigated in detail in the Reagan "Star Wars" program of the 1980s, backed by one Edward Teller. Tests were carried out by surrounding the nuke with bundles of rods to create a one-pass laser. Apparently it was nowhere near efficient enough to be used in a military context. ...

3

From scholarpedia: The Unruh effect is a surprising prediction of quantum field theory: From the point of view of an accelerating observer or detector, empty space contains a gas of particles at a temperature proportional to the acceleration. Direct experimental confirmation is difficult because the linear acceleration needed to reach a temperature 1 K ...

2

The ability of a lens to concentrate power is a function of several parameters: area of the lens focal length of the lens absorption of power in the lens aberration of the lens For an ideal (thin, spherical, circular) lens of focal length $f$ and diameter $d$ you can estimate the diameter of the image of the sun (which is roughly 0.5° across as seen from ...

2

You use the first formula you gave when you have (entirely) uncorrelated errors where the standard variances (the squares of the standard deviances) add. Gaussian distributions of errors are usually assumed. You might use the second formula if your errors are perfectly correlated, but even then only as a worst-case measure (if you know the correlation, you ...

2

Yes, wikipedia has a table which lists the 19 free parameters that need to be tuned by experiments. These include, as you already said, the masses of the elementary particles including the Higgs Boson, and some other notable ones are: CKM Mixing angles and CP-violation phase. Gauge coupling of he three symmetries (U(1), SU(2), SU(3)). Higgs VEV

2

It's the response of the system to a stimulation at zero frequency. In other words, it tells you the displacement of the system in equilibrium under a time independent force. Let me give an example. Consider a mass on a spring with friction and an external force $F_{\text{ext}}(t)$. The friction force is $$F_{\text{friction}} = -\mu \dot{x}$$ so the ...

2

First up thanks to all who took an interest especially @irishphysics who stuck with the question for some time. It turns out that the phenomena was analysed and solved by Lord Kelvin and is known as the Kelvin wave pattern. The pattern itself is the result of a spreading pressure wave which manifests itself as the curved diverging wave crests (the ones I ...

2

Short answer: We can measure their energy and momentum distribution functions in the nucleus. We do this by interacting with them individually, either knocking them out of a nucleus left otherwise undisturbed (quasi-elastic scattering) or by exciting them to higher energy states inside the nucleus (many inelastic scattering reaction backed up by data from ...

2

When power is consumed, the voltage and current rises and fall together (with some variation due to power factor). As you consume energy from the grid the voltage generally stays the same but the current rises and falls depending on your consumption. As you reduce your demand to zero, the current falls to zero, then when you start feeding into the grid, ...

2

You can have a pool of water and place a cardboard or a piece of plastic with two slits in the middle. Just create a wave that goes through both slits and the waves should start interfering.

2

The first to do something equivalent to that were Pound and Rebka who first measured the gravitational redshift in 1959. I'm not aware of anyone who actually used a Michelson interferometer in a upright orientation.

2

Compton observed that the scatter angle of a photon was the same regardless of the material used to effect the scattering. He concluded (correctly) that whatever it was that was doing the scattering did not seem to be specific to the material in question. So what are the candidates in the material? The nucleus. Definitely different for different materials ...

1

You are correct that time and frequency domains are just Fourier transforms of each other. However you only have full information if you have amplitude and phase information (as opposed to a power spectral density which is only amplitude information in the frequency domain). Frequency spectra might tell you that you have multiple modes that exist, but it ...

1

The relativity of simultaneity is not an axiom, the axiom is that the light velocity is the same in every frame of coordinates. A spot of light travels at the same velocity, c with respect to you, and at the same velocity $c$ with respect to a traveler traveling with respect to you at an arbitrary velocity. So, assume that you send two spots of light to ...

1

I was unable to see any Fraunhofer lines with the sun light, despite using a focusing lens. However, I tried examining the light of a fluorescent bulb instead. I didn't manage to project the image on a sheet of paper, but I was able to take a direct picture of the image in the prism. The result is a bit more satisfying: / Are these four lines a ...

1

In quantum mechanics, a system is represented by a wave function. The wavefunction is a sort of blob spread out over $x,p_x$ space and $\delta x, \delta p_x$ represent the size of the blob. At a given time the wavefunction of a system has to be spread out in x if it is highly peaked in $p_x$ and vice versa because $\delta x \delta p_x \geq \hbar$. The ...

1

It would be possible, and not even terribly difficult, to have a faucet whose stream, viewed at a moment in time, would appear as a spiral. A double-spiral diamond pattern would be harder, but should by no means be impossible, though unless the diamonds were rather coarse they would tend to become blobby as water moved away from the faucet. The key ...

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