# Tag Info

13

Given that most green pointers are frequency doubled from a 281.8 THz infrared laser ($c$/1064 nm), it's possible that you have a two frequencies $f_1$ and $f_2$ in the original infrared laser (i.e., it is multimode). After passing through the "frequency doubling" nonlinear crystal you see three frequencies: $2 f_1$, $2f_2$, and $f_1 + f_2$. It looks like ...

10

Short answer - yes, everything in the circuit can contribute. But usually, an ohmmeter is zeroed with the probes in place - in other words, whatever resistance the probes represent is taken out by the meter. There are two other factors that play a role, especially when you try to measure small resistance. The first of these is contact resistance: it is ...

8

As John Rennie answered it very clearly, I would like to add some more details too. See, around early 1900 the idea of atoms was floating around the scientists' heads. At first everything was theory, but these things happened: You certainly heard of Joseph Thomson's cathode rays. Well, he actually calculated the ratio Q/m of atoms. (You can search any of ...

5

There is no such experiment, though there are lots of experiments where the number of electrons in an atom are measured as a side effect. We know atoms are electrically neutral so there must be equal numbers of electrons and protons. We know successive elements in the periodic table are built up by incrementing the number of protons, so we know how many ...

4

Or at least "functions" as a monopole? I'm afraid not. A magnet is a magnetic dipole and there is, as far as I know, no configuration of magnetic dipoles that can give a monopole field.

4

I don't know the "official" answer but here is what I might try. I am hoping that others will contribute to make this a "good" answer. First - we were not told whether the wavelength of the laser is transmitted at all by the blue foil; but since blue foil typically absorbs red light, and most laser pointers are red (I have a blue one but they are ...

4

If the accuracy of the experimental measurements is smaller than the width of the gaussian then the shape describes the probability distribution one should get for any decay in particle physics. If the experimental accuracy is larger than the width of the decay then one gets a gaussian from the randomness of the experimental error . Example J/psi in ...

4

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 ...

3

As irish guessed in the comment, this is about beam alignment and tuning. A high intensity beam can damage the beam pipe (as in cut right through to the helium jacket) or cause a unusually hard superconducting magnet quench. The former is disastrous and the latter has some potential outrun the quench protection with similarly unhappy consequences. Having a ...

2

The curve you show is not a Gaussian. It is a binomial distribution with $n=100$ and $p=0.5$ (if it is an unweighted coin). This arises from processes where there are two outcomes. It approximates a Gaussian/Normal distribution when $n$ is large. This distribution has little to do with particle detection other than perhaps as a means of explaining what is ...

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

As the comments indicate, the answer truly is that the electrons in the solid are not really free. But wait, I hear you say -- the free electron model approximates the electrons in the solid as a free gas of electrons. It certainly isn't perfect, but it can't be that poor of a description. Yes it can, and I'll explain why. Consider what it means to say ...

2

Those two are answers to different questions. When you talk about the $\nu =$ 9.192631770 GHz, $h \nu$ is the separation between the energy levels involved in the transition. This is precisely defined. The second concept you talk about is the amount of time the atom remains in the excited state, also known as the excited state lifetime $\tau$. These two ...

2

A few comments, since it seems you're about to rephrase this question. When dealing with the caesium standard, you can essentially forget about the energy (of the excited state, and of the photon). What matters is the frequency, and the only uncertainty principle that ever gets involved is of the form $\Delta\omega\,\Delta t\gtrsim1$. This is a standard ...

2

The latest data is from the Planck satellite, and you can find the results in this 15MB PDF. The matter and dark energy densities are; \begin{align} \Omega_M &= 0.315 \pm 0.017 \\ \Omega\Lambda &= 0.686 \pm 0.020 \end{align} So we get a total density of $\Omega = 1.001 \pm 0.026$. So within the 2.6% experimental error spacetime is flat.

1

No definite answer to this question, the effect in some sources is accepted and other sources dispute it. From Wikipedia: The hypothetical Unruh effect (or sometimes Fulling–Davies–Unruh effect) is the prediction that an accelerating observer will observe black-body radiation where an inertial observer would observe none. In other words, the ...

1

I agree with Alfred Centauri that there is no configuration of a monopole, but on the second question, depending on how big the surface of the magnetic floor is, the strength of the magnets, and some other conditions I would imagine that it would levitate over the floor. On the third question, I believe that if it were a perfect sphere, the center ball would ...

1

I would like to bring the ladder paradox here to explain simultaneity of events.A ladder (an inertial frame) is moving horizontally with a relatively high constant speed with respect to a garage (another inertial frame). The garage has an open door where the ladder can not actually enter if the ladder was at rest in the garage's frame but that is not ...

1

Regarding your assertions: Events $\varepsilon_{AJ}$ and $\varepsilon_{BK}$ were simultaneous in the inertial frame of participants $A$, $B$, $M$. This is a perfectly reasonable statement and it is the sort of language used in everyday physics. Participant $M$ was the middle between $J$ and $K$, in the inertial frame of participants $A$, $B$, $M$. ...

1

The Walter Lewin Classical Mechanics lectures contain lots of good demonstrations. https://www.youtube.com/playlist?list=PLUdYlQf0_sSsb2tNcA3gtgOt8LGH6tJbr

1

The original problem can be seen in terms of energy and momentum conservation. Before scatter, there are two particles in the center of mass and the center of mass has an invariant mass larger than the mass of the electron. For total absorption of the photon there would be only the electron left. As the electron has a fixed mass and at the center of mass ...

1

The dripping would occur as you describe it, if the drip ends of your tube or tubes is low enough to let gravity overcome the capillary action. That is what prevents a perpetuum mobile: Just as the water from the container is sucked into the tubes, water from the opposite end is also sucked in. To remove it, you have to expend energy, the same (in steady ...

1

The elucidation of the structure of DNA began as an exercise in x-ray crystallography. If you shine a beam of x-rays through a crystal, it will act like a diffraction grating, and the points of constructive interference will show up as dark spots on photographic film. This had been used for decades to determine the structure of relatively simple molecules. A ...

1

anna v's nice answer didn't go where I expected: the big acceleration at the LHC isn't in the accelerator, it's in the collisions. Let's suppose we have a proton in the LHC that undergoes an elastic, billiard-ball type collision and ends up with its original momentum in the opposite direction: \begin{align} \vec p_\text{initial} &= +7\,\mathrm{TeV}/c ...

1

There is no fundamental difference between the signatures found in the two works (Kouwenhoven and Yazdani). Both are tunneling spectroscopy, which roughly measures whether there is a zero-energy single-particle state in the spectrum. Yazdani's setup allowed him to do measurement away from the edge, so that the localization of the edge state can be directly ...

1

Newton's law of cooling is an empirical observation not a fundamental law. The cooling of a body in air is a formidably complicated process because the cooling is dominated by the air flow, and the air flow is complicated to model. However we find from experiment that over a limited range of temperatures the cooling rate is proportional to the temperature ...

1

Use your power meter and graph paper to map out the reflectivity as a function of angle. The Fresnel equations (plots shown below) are rather sensitive to the relative indices of refraction of the glass-foil interface. If the index of refraction of the foil is higher than the glass then you will hit a plateau above the critical angle at which all of the ...

1

Does Sphere C have any effect of on the gravitational force between A and B? Nope. C does not make any difference to the force between A and B, but its introduction has the effect that the net force on A has contributions from both B and C. (Likewise for the other spheres too.) This is because gravitation obeys the principle of superposition. Is ...

1

The LCD panel consists of elements shown in the figure below. The unpolarized light from backlight panel travels through polarizer, after which the light is linearly polarized. TFT panel controls the voltage on the liquid crystal, voltage applied will cause the liquid crystals to "twist" and thus rotate the polarization of the light. Light then passes the ...

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