# Tag Info

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All electromagnetic waves (long wave, radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays) are produced when electrons are accelerated (not necessarily transmitted). Electrons themselves are not transmitted and thought of as electromagnetic waves in most of the spectrum except in the case of x-rays, or synchrotron radiation. In the ...

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Yes, alternating current will radiate electromagnetic waves. For example, in telecommunication, the transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves.

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When you say the particles cannot interact, yes it will take at least 100 photons to excite all the particles. You could have one particle absorb a photon, then radiate a lower energy photon that is absorbed by another particle but you have ruled that out by saying no interaction.

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I don't think that holding the fob to the head does much good, but what does make a huge difference is holding it high up. The simplest flat plane multipath reflection model predicts that the received power is proportional to $$\left(\frac {h_1 h_2}{R^2}\right)^2$$ where $h_1$ and $h_2$ are the heights of the transmit and receive antennas and $R$ is the ...

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Unfortunately I can't remember where I read this, but I recently read a theory/explanation that it's merely because the key is being held higher up.

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Are you sure holding it to your head really makes it better? Your experiment is very poorly designed because you have only sampled instances where the remote wasn't working when your head wasn't in the picture. This is blatant selection bias. No doubt, putting the remote near your head (or anything else conductive) will significantly alter the ...

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Remote "key fob" designers intentionally limit size so they conveniently fit in your pocket. However, the convenience comes at a big price - the tiny loop antenna inside is extremely inefficient, transmitting less than 10% of the energy pumped into it, while the rest is simply converted into heat. When holding your remote to your head, your arm, shoulder ...

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The Earth and the Sun has magnetic fields which shields us from cosmic rays, as a charged cosmic ray particle will loose kinetic energy when its direction is perpendicular to the magnetic field. So what happens to the kinetic energy of the cosmic ray particle? According to the first law of thermodynamics it can't just disappear. It goes to the magnetic ...

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"What does the peak stand for?": If you consider infinitesimally small ranges of wavelength values, the energy density (intensity) will be maximal at the peak. "And what does the graph tell us?": Considering a place of uniform temperature, with radiation in equilibrium with the surroundings, such as in a uniform temperature box, the graph tells us how ...

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The way it works has nothing to do with your body. Remotes have their antenna as a more or less circular trace on the board (a loop antenna). The strongest signal is when the top or base of the remote is pointed at the receiver. The weakest signal is when the fob is pointed 90 degrees away, such as when pointing it like a TV remote. Guess which way most ...

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The term "Tokamak" refers to a design, not a size. The planed ITER reactor has the goal of 500 megawatts output. So it would take approximately 300,000,000 such reactors to produce the same power as the solar energy reaching the Earth. https://www.iter.org/factsfigures

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This is a really interesting question. It turns out that your body is reasonably conductive (think salt water, more on that in the answer to this question), and that it can couple to RF sources capacitively. Referring to the Wikipedia article on keyless entry systems; they typically operate at an RF frequency of $315\text{ MHz}$, the wavelength of which is ...

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Here's the logic (well a particular rendition): Recall that $n$ is defined as the ratio of the speed of light $c$ in vacuum to the speed of light $v$ in the given medium; \begin{align} n = \frac{c}{v} \end{align} Note that in a linear medium, Maxwell's equations are exactly the same as in vacuum, except $\mu_0$ and $\epsilon_0$ are replaced by $\mu$ and ...

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I would make a flag from iron oxide (red), platinum (white), and lazurite (blue). It won't wave in the wind, but it will retain the color. The base would be a platinum plate, of course. I would made a really large one, so that people wouldn't complain that it was too cheap.

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The Apollo 11 flag was included almost as an afterthought. It was just a month or so before liftoff, and someone at NASA slapped themselves on the head and said, "we need an American flag to plant at the landing site!" Someone rushed out to a local store (Sears?) and bought a standard nylon flag, which went to the Moon. Besides being bleached out by solar ...

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I think your question is either: what FREQUENCY of alternating current, as in the case of a local open core transformer, or else what frequency of RF energy (as in microwave, radio wave, etc.) could be used to power or provide charge to laptops batteries 'wirelessly'? Not just any frequency you want, that's for sure. In the United States, the FCC takes a ...

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I thought the phones picked up the longer wavelengths due to an enlarged field, which was electrically generated, much like tv aerials needing a current..

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I assume that by zero frequency, you mean zero momentum transfer. Zero momentum transfer corresponds to the $k=0$ value of the Fourier transform. The value of this part of the fourier transform is the integral of the scattering strength over all space. So you can think of this value as being the total amount of stuff that is there. Another thing to keep in ...

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Birefringence. Many substances such as cellophane or antistatic tape have two indices of refraction, a 'fast' axis, and a 'slow' axis, not necessarily at right angles to each other. Minute changes in the thickness of a birefringent material will appear to produce different colors between crossed linear polarizers because different thicknesses of ...

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The field itself has to be real, of course. The imaginary part is added as a computational aid. Dealing with an exponential, whose derivative is itself, is much easier than dealing with a cosine. So we add the imaginary part, do our computation, then dump the imaginary part of the result. It's all simple when the computations are all linear. Sometimes, ...

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Light changes direction when passing through a prism because the density of air is different to the density of glass. Therefore the speed changes, when something (i.e. glass or a prism) is optically dense it is harder for light to travel through it, thus making it's speed decrease. When the waves meet the prism they slow down, so if they meet it at an angle ...

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In fact a sharp boundary is not required. It is sufficient that the charge density $$ρ(\bf{x})=∂_{x}⋅E(x)=[∂_{x}ɛ⁻¹(x)]⋅D(x)$$ is not constant. The wikipedia article is somewhat outdated. A fairly recent discussion (of which I was one of the authors) can be found in B. Lastdrager, A. Tip and J. Verhoeven: Phys. Rev. E 61, 2000, p 5767. It presents a detailed ...

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Alfred Centauri has almost answered the question for you (actually he has), but he's using knowledge about and properties of Maxwell's equations that it sounds as though you haven't yet met. Maxwell's equations are covariant with respect to Lorentz transformations. That's a fancy way of saying that they keep their exact same form, and must foretell the same ...

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$400$ - $700\text{ nm}$ corresponds to about $430$ - $750\text{ THz}$ ($10^{12}\text{ Hz}$), not $\text{MHz}$ ($10^6\text{ Hz}$). To convert from wavelength to frequency, use $$f = \dfrac{c}{\lambda},$$ where $\lambda$ is the wavelength, $f$ is the frequency and $c$ is the speed of light. So, for $400\text{ nm}$, this is: $$f = ... 0 Reflected light can be though of as originating in oscillating charges in the medium. The incident light causes the charges to oscillate, and the oscillators generate the reflected light. This process happens almost instantaneously. The atoms in the medium are oscillating coherently (in step) with the incident radiation. The frequency of the light is ... 1 Usually the Newtonian limit is described as taking v << c but a much better way to express it is saying that the kinetic energy is much less than the rest energy$$ \frac{1}{2}m v^2 << m c^2 $$of course this runs into trouble when we talk about photons since we don't have a well defined concept of velocity, in the Newtonian sense. This is ... 1 For a particle of fixed mass m moving in a fixed gravitational potential \phi(\vec{r}) the motion is independent of the mass of the particle. The equations are$$ \vec{F}=-m\nabla\phi $$and$$ \vec{F} = \frac{d\vec{p}}{dt} = m \frac{d\vec{v}}{dt} $$It's clear that the m's cancel when combining these equations. So from this point of view it doesn't ... 0 Actually a much more difficult question is why is glass transparent and does not SCATTER? Lack of absorption is just one explanation. But take a ceramic. It does not absorb (e.g., toilet bowl) yet it is not transparent. So why is glass transparent. This does NOT really has a trivial solution. 2 When you say "without altering the actual momentum of it" is that really true?$$ E^2 = p^2c^2 + m^2c^4  so for a photon $E = pc$, since rest mass is zero. Now according to your first "traditional" calculation of m, we would have $E = pc = m_1c^2$, and therefore $p=m_1c$, where $m_1$ is mass according to the first "traditional" calculation. For your ...

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You also you need to take into account the radiation that is generated by the interactions within the Al (unless that is neglected). This modifies the thickness of Al required. The correct name for that term is 'Buildup Factor'. There is a chapter in Cember & Johnson that explains it very nicely. A.

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Firstly, if your waveguide is a hollow conductor, it cannot support TEM modes. There must be at least two separate (electrically insulated from one another) conductors in the waveguide's cross section for TEM modes to propagate. The reason is that the transverse field dependence of a TEM mode is the same as that of a static field, as I explain in detail in ...

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Here's my visual approach to answering your question: the "spherical electrical waves" that you're referring to are just a way to represent the wave crests of light. When considering the oscillating electric field component of the electromagnetic wave, the individual waves propagate through space symmetrically in all directions when being emitted from a ...

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I am not sure if my answer is correct, from what I understood: (i) At the relativistic limit, $m<<E$, so the second and third terms in (6.15) will be negligible, just as you said. (ii) P&S is aiming at $\hat{k}$ parallel to $\mathbf{v}$ or $\mathbf{v}'$ and integrating around $\theta=0$, since (6.15) peaks there (also ref my comment below ...

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Just to add an additional twist to the very good answers by Colin K and gigacyan. I have actually been in situations where those exact patterns were real. I used to design grayscale microlenses (manufactured with computed masks) where the finite resolution of the design (driven by the resolution of the lithographic grayscale pixels) actually caused those ...

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The Wikpedia article on solar cell efficiency gives a number of reasons that solar cells are less than 100% efficient. One of the large ones is the thermodynamic limit-a photon of less energy (longer wavelength) than the silicon band gap cannot produce an electron and one with higher energy can only produce as much voltage as the band gap. Even if you ...

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No energy conversion process completes at 100% efficiency. Using the sun, gasoline or nuclear, none of these will generate power at 100% of total potential power available. That figure of 1KW/m^2 is for total available light energy correct? Due to how solar panels work (I don't think I have enough knowledge to speak on this part directly) solar panels are ...

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A quick Google search led me to this 2010 paper by Rizzo et al (that's arXiv link, here's the IOP science link). The article states, ...the inverse Cotton-Mouton effect (ICME in the following), [is] a non linear optical effect that in principle exists in any medium. In the presence of a transverse magnetic field, a linearly polarized light induces a ...

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The explanation is very simple! The reason light changes direction ("bends") when traveling through glass, is because light travels slower in glass than in air. If now, you also want to know why light travels slower in glass than air, it is because the density of glass is higher than air and the electromagnetic fields of the glass molecules interfere more, ...

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Photons or cosmic rays don't (normally) emit gravity waves. Consider the comparison with radio waves. A moving electron doesn't emit radio waves. It has to be accelerating to emit EM radiation. Specifically radio waves are only emitted when there is a changing dipole moment. So you wouldn't expect a particle moving at constant velocity (photon or ...

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In light of this, why do photons traveling from the most distant reaches of the observable universe not lose energy due to the gravitational radiation they must emit? There is a misconception here in "gravitational radiation they must emit" . There does not yet exist a unified theory of elementary particles and the three interactions well described by ...

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Kyothe was on the right track, but in fact we do radiate in the visible, just in such small amounts that it's not detectable for all practical purposes. If you look at the referenced Planck (black body) curves for objects around human body temperature, the short-wave tail is nonzero in the visible range, but it's there.

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A little google searching would have had you your answers pretty quickly. But I was bored so here they are: In answer to the first question: "The wavelength of radiation emitted depends on the temperature of the objects. Such radiation is sometimes called thermal radiation. Most of the radiation emitted by human body is in the infrared region, mainly at ...

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We radiate infrared rather than UV or visible light because we aren't hot enough. See http://en.wikipedia.org/wiki/Planck%27s_law for more details.

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If you read the wikipedia article on orbital angular momentum of light you will see that in the first place it is a classical electromagnetic concept, where the light has a vorticity, i.e. a helical motion around the axis of the vortex. When one goes to the quantum detail of photons one can define an OAM against this classical axis for each photon in this ...

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The answer to your question is generally yes, but it depends on how the AOM is driven. Typically AOMs have a piezoelectric transducer on one side of the crystal. In this case the frequency of the diffracted beams is shifted; if the laser frequency is $\omega_0$ and the modulation frequency is $\omega_m$, then the light in the first order beams will have ...

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The acoustic wave in the material causes a variation in refractive index and the amount of light scattered at a particular angle (its similar to Bragg scattering) depends on the intensity of the modulation. The scattered light does carry both frequencies in the form of blue or red shifting. It shifts by mf where f is the driving frequency and m is the order. ...

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With the setup you describe I would expect to get 60% without too much effort. Optimizing the mode matching to the fiber as described by @jayann should get you up to 80%. An experienced person could do all of this in a day, but if you are new to alignment of optics then it will take longer. If you are only getting 30%, then either your fiber is bad or ...

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When you are using APC facet of your receiving fiber, you should set a proper angle for that fiber due to misaligment between laser beam (it can be considered to be plane wave) and the fiber. Once you realign the APC fiber with a small angle (let's say 8 degree) then attach to the laser beam path, you will increase the coupling efficency.

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