# Tag Info

## Hot answers tagged experimental-physics

25

Yes it works. But let's not use it on a massive scale, lest we damage the ecosystem (tip of the hat to @phi1123). A hint to the mechanism can be found in Behroozi et al (Am J Phys, 2007) They state in the abstract: From the attenuation data at frequencies between 251 and 551Hz, we conclude that the calming effect of oil on surface waves is principally ...

7

Before everyone freaks out, no, you don't use petroleum oil. You use vegetable, fish or animal oil. In earlier times, whale oil would be used. The OP's picture looks like a fuel oil leak, not an attempt at wave calming. I have seen references of this technique being used since at least the early 1800s, probably much earlier. Ernest Shackleton made use of ...

6

The spin of the neutron was measured by the Stern-Gerlach experiment by Sherwood, Stephenson and Bernstein (1954) (sadly paywalled, free links welcome), Abstract: A neutron beam was polarized by total reflection from a magnetized iron mirror. The beam was then analyzed by passing it through an inhomogeneous magnetic field. From the deflection pattern ...

4

Do we have any tunneling current for $0 < V \leq V_c$? Yes. If yes, then why don't we show it in the diagram? It is in the diagram, you just have to understand how that diagram was measured. Junction basics The Josephson junction is governed by two equations \begin{align} I &= I_c \sin(\delta) \\ V &= (\Phi_0 / 2\pi) \dot{\delta} ...

4

The hydrogen discharge tubes typically used in student labs are not designed for long-term use. After a couple of years, the tubes leak and air gets mixed with the hydrogen. This causes them to get dim and the weaker lines are almost impossible to see. It has nothing to do with the power supply and everything to do with how new the tube it and how many ...

4

ALICE is a heavy ion experiment at CERN. Here is a lead lead collision One of the LHC's first lead-ion collisions, as recorded by the ALICE detector. Thanks to the advances of computing the vertex is determined by the tracks , measured and pointing back to it, even though there are thousands of tracks from each vertex. Certain tolerance assumptions ...

4

The company TeachSpin builds a two-slit interference instrument for use in the advanced/modern physics lab. There are several descriptions and schematics at that website. They do not have a lens before or after the single slit. The single slit is physically close to the source. I've used the instrument several times and it gives beautiful results for both ...

4

Actual number of events measured will depend on how long an experiment is run, the efficiency of a detector, the size or thickness of a target, the intensity of an incoming beam among other things. Each of these is unique to a given experiment. Science is done with the expectation of reproducibility, so these factors which distinguish one experimental setup ...

4

The underlying principle is to use interferometry and the Doppler effect to remotely measure the velocity of a reflecting surface. When a moving object is illuminated with coherent light it reflects it with a wavelength shift proportional to its velocity. This is the well-known Doppler effect. The frequency shift relates to the source's velocity as ...

3

Are you sure that the single slit between lenses 1 and 2 is a slit and not a pinhole? If I were setting this up without a laser, I would use a pinhole below the diffraction limited spotsize of the first lens at the focus: this gives you an aberration free spherical wave at the output of the pinhole (same idea as a point diffraction interferometer / ...

3

Every few year the Committee on Data for Science and Technology (CODATA) publishes recommended values of the fundamental constants, see http://www.codata.org/. They use the most accurate experimental results available, so yes, the values of the fundamental constants can -- in principle -- change. But what is more likely, is that the number of significant ...

2

Depending on wavelength, just with an aperture diffraction will kick in few cm after the aperture, and you'll get rings opening up with further propagation. For some applications that could be ok, especially if you use the beam right after the aperture. Practically, the way I would change the beam shape from elliptical 2x4mm to circular 1.5mm is putting in ...

2

I am sorry to disappoint you, but there is no such formula that you can just apply. This is because it strongly depends on how and under what exact conditions and with wwhich tools you did the experiment. Think of this: If every methanol molecule reacts (burns) at once all at the same time, then the exact same amount of energy is spent, but it went really ...

2

Because rate is often the right observable to report. The number of event depends on how long you observe, but to within statistics (corrected) rates can be compared between similar experiments without correction.

2

Use a sodium lamp positioned above the prism and slightly to the side to create a reflection at the interface. Look for interference patterns at the prism/prism plate interface. If the spacing between dark fringes is small (and you have many fringes), you have a problem. If you have very few fringes and the spacing is large, the interface is close to being ...

2

To answer your questions: Yes, fibreoptics transfer light. Maybe. I'll discuss that now Fibreoptics are strands of glass, they're CRAP at going around corners, I mean seriously crap, communications fibre is VERY THIN. Even then it can't go around bends well, they test it at every stage during laying. However with communications stuff the path matters ...

1

When you talk about the speed of gravity, you are talking about the speed of gravity waves. If something jerks to one side or changes shape in a way that the change in gravity could be detected at a distance, the progress of that change through space is nothing other than a gravity wave. People have been trying unsuccessfully to directly detect gravity ...

1

Some background. You want to detect the image of an object. First, either 1) you illuminate it with some light source [a lamp, the sun] or 2) the object itself radiates light out [a star, a fluorescent sample]. Imagine to divide the object in many small parts (voxels): to reconstruct the image of the object, you need to detect independently the light coming ...

1

It has been pointed out that this cannot simply be done by examining the mass distribution (first and second moment of mass). But there is a way to "look inside" most common objects: Take a CT scan. Not sure if you consider that "typical" lab equipment - but it's equipment I have in my lab... Of course depending on the size of the object and the material ...

1

we often confuse or loosely say that friction opposes motion but it should be kept in mind that it opposes the "relative motion" so if two bodies are moving opposite to each other then we need to change the frame of reference from earth to the body and check what is the direction of relative velocity. once determined we can clearly say that the direction of ...

1

I'm not an optics guy, but I can think of a few issues you'd want to think about until a pro comes a long and explains it all to us: The beam will diffract from the new aperture affecting both collimation and coherence length. Only a concern for very small beam diameters or long optical paths; and something that any other method for reducing the beam ...

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