# Tag Info

## Hot answers tagged experimental-physics

11

Classical electrodynamics is certainly studied in curved spacetimes to understand real phenomena. What better place for gravity and electromagnetism to work together than the ionized, magnetized plasma surrounding an accreting black hole? In particular, we observe quasars with extremely powerful relativistic jets. Quasars are the supermassive black holes at ...

7

Short answer: you don't. Slightly longer answer: You're using beams of particles, and you focus each of them as much as you (practically1) can so that the particles in each beam are reasonably close together. The result is a wide variety of interaction distances from far apart through near misses to closer interactions still. You mentioned electrons ...

6

It's only "sticky" when you stick it to something that was initially warmer than freezing. Let's say you stick your finger against a (very cold) ice cube. Two things happen in sequence: The heat from your finger transfers into the ice and melts it slightly, forming a thin water layer. The heat dissipates further into the cube, and the water refreezes. ...

4

It's really complex, and the answer from Shep is a bit imprecise. Ice at temperatures just below freezing has the remarkable property of not being frozen on the surface. There is a extremely thin layer of liquid water on the surface. How thin? 70 nm at 272 K, but only 10 nm at 262 K. This water layer can act as a lubricant, but with less lubricant the ...

3

I can't find details on the pulse energy and duration of the LCLS, but it's entirely plausible the power could be greater than the national grid of a large country. The power is energy divided by time, and if the pulse length is very short then even a modest pulse energy produces an astronomically high power. For example the laser at the National Ignition ...

3

Usually this is called "hysteresis" - a bit of "memory" of the last state (definition from Google): the phenomenon in which the value of a physical property lags behind changes in the effect causing it, as for instance when magnetic induction lags behind the magnetizing force. It can also (in the case of mechanical instruments) be known as "backlash". ...

3

The $W$-boson was discovered in 1983 at the UA1 collider Experimental Observation of Isolated Large Transverse Energy Electrons with Associated Missing Energy at s**(1/2) = 540-GeV UA1 Collaboration (G. Arnison et al.), Phys.Lett. B122 (1983) 103-116, Experiment: CERN-UA-001, Feb 1983 There's no evidence in the paper of a precedent in high-energy ...

3

Jefimenko's book introduces currents with experiments, and just reading his book felt like you were seeing the experiments being done right in front of you. I didn't read the whole book, so I don't know if he finishes the job, but he introduces currents as real things (for your system of units, and as a physical observation of fact), and then gets charge ...

2

If the concepts of E and B are unknown, the four Maxwell equations won't be enough. You also need to find out about the Lorentz force equation F = q(E + v x B). I'm assuming the concept of charge is also unknown. I'm also assuming that you're asking this question because you're planing an undergraduate lecture of some sort. I'd start with a justification ...

2

I have demagnetized materials to try to eliminate magnetic fields from experiments. I took a coil of wire and passed AC mains through it to create an oscillating magnetic field - The AC was connected through an AC transformer like the one in the picture. slowly over time the voltage was reduced so a smaller and smaller magnetic field was used. To ...

2

The first part of the question If a theory gets two predictions right, how likely it is that the rest of the predictions are true too? << can not be answered since even the wrongest assumption can lead to 2 right predictions (and an uncounted bunch of wrong ones). Two opposite theories can have two simililar predictions which of course does not ...

2

A very simple example of electromagnetism in curved spacetime is the observed bending of light due to gravitational fields. Usually this is presented as the statement that "photons follow null geodesics." This statement can be derived in a geometric optics approximation to Maxwell's equations in curved spacetime (i.e. it is not just an additional postulate ...

1

There is in fact a change in slope - you can see this when you fit a straight line through the data, then subtract it to look at the residuals: It seems that the first three data points lie on a steeper curve than the remainder - as though something changed in the setup (did thing heat up?) Residuals plots are an essential tool when you analyze data that ...

1

Even I didn't get you but I may help you how much I can by describing your case. Your case have two bodies which are being rubbed against each other in opposite direction with constant acceleration. The definition of friction is, "The resistance which either one of the bodies offers to this motion is called the force of friction and is said to be due to ...

1

Relativity of simultaneity is a logical consequence of c's invariance. Time order reverseals have not been tested directly as far as I know, but since the invariance of c from which the relativity follows has been tested in a lot of experiments I would say that the thought experiments regarding this issue are solid.

1

You should take an electromagnet that operates on some frequency (tens of Hertz) and creates enough large magnetic field to magnetise your permanent magnet. Then you switch on your electromagnet in the vicinity of the permanent magnet and go slowly back from the permanent magnet at the distance of several meters. After this the permanent magnet should be ...

1

The hydrogen molecule where the proton spins form a spin singlet $$\left|s_1,s_2\right> = \frac{ \left|\uparrow\downarrow\right> - \left|\uparrow\downarrow\right> }{\sqrt2}$$ differs in energy from the spin triplet with $$\left|s_1,s_2\right> = \frac{ \left|\uparrow\downarrow\right> + \left|\uparrow\downarrow\right> }{\sqrt2}$$ by a ...

1

1) Kirchoff Voltage law in circuit(generally with an inductor) for faraday's law in scalar form. 2) Cheap electrification experiments for coulomb's law. 3) Electromagnets in dc and Capacitors in ac circuit for ampere-maxwell law. You will have to measure force/torque patterns to get the concept of E, B fields for full generality of the above. Iron fillings, ...

1

I think I actually have an answer to this question even though I put a bounty on it. The idea is that the amplitude is maximal when the $W$ bosons are produced on-shell (since the propagators are the largest in this limit). This allows us to treat the creation of the $W$'s separately from the rest of the diagram. The momenta of the particles in the lab ...

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