# Tag Info

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 ...

0

The persistence of water vapor in the air depends on updrafts of warm air. As warm air rises, it carries humidity that condenses into vapor droplets when it hits higher layers of colder air. Once condensed, the vapor tends to fall. But continuously rising warm air replenishes the fallen droplets, so the rainbow phenomenon persists as sunlight is refracted ...

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 ...

0

Best hypothesis so far is that as gas density increases the transducer couples more efficiently to the medium, giving the impression of a decrease in absorption coefficient due to the increased amplitude at the receiver.

3

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 ...

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 ...

0

The force of humans on the earth is already there before they jump, because people are standing on the earth. With their weight distributed over the entire earth, their jump (which might briefly increase the force by 2-3x) will have no effect. Since you said they would be jumping in the sea, there will be a very small increase in the sea level. Mass of all ...

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 ...

-6

What is the reason that like charges repel and unlike changes attract each other? It's because of the "spinor" nature of such charged particles: GNUFDL spinor image by Slawkb, see Wikipedia A spinor is a mathematical entity which is associated with a a spin ½ geometry which in turn is associated with Dirac's belt and the Dirac equation. That's "a ...

-1

Unfortunately, this is one of those "why" questions that can't really be answered. Sure, I could make a deeper model but that would just be kicking the can down the road. See for instance: https://www.youtube.com/watch?v=MO0r930Sn_8

0

Sometimes you will see statements like 'some of the lift is caused by Bernoulli's principle and some of it is caused by Newton's laws", but this is the wrong way to think about it. The fact is that 100% of the lift can be explained by Newton's laws and 100% can be explained by Bernoulli's equation. Both approaches explain 100% of the lift. The problem is ...

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 ...

0

There must be some asymmetry at the start. It can go either way, positive or negative. It's like balancing a razor blade on edge, and "falls" one way or the other. But, under humid conditions, the Kelvin generator gives zero output. Build it, turn on the water, and nothing happens. This occurs because a many-megohms resistance appears across all the ...

0

50 ohms total? And the coil resistance is much lower than 50 ohms? When you apply 120V, the resistors will quickly burn inside. They won't be 50 ohms anymore (need to measure their resistance with a meter.) The resistance becomes high, and the current drops far below 2.4amps. Resistor power is V^2/R = 120*120/50 = 244 watts, so your twenty-watt ...

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 ...

0

I shall first appeal to one of the key points of relativity: If you are 22 years old, like me, I can only have affected things up to 22 light years away from me. Things beyond that are untouched by my existence in every sense. If gravity were faster than light (by say a factor of 2) I could then have affected things up to 44 light years away! This is ...

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 ...

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.

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 ...

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 / ...

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 ...

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 ...

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 ...

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 ...

0

The only answer I can think of would be: 1- how much substance is disolved in the water, and 2 - at what elevation are you boiling your water. Salt water has a higher boiling point than pure water. Reduced ambient air pressure will lower the boiling point.

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 ...

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 ...

0

The truth of the Lorentz transformation as an accurate description of the co-ordinate transformation between relatively uniformly moving observers needfully implies relativity of simultaneity. Contrapositively, the Lorentz transformation cannot be sound if simulteneity is not relative. So, in the sense that the soundness of the Lorentz transformation has a ...

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} ...

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 ...

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

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 ...

0

I think there is still a current flowing. I found this picture on this website. The gist is that above a certain voltage $V_c=2E_g/e$ (twice the energy gap divided by elementary charge), the voltage large enough to overcome the band gap and Cooper pairs can flow. EDIT: Also look at this excellent post.

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