# Tag Info

28

In general the answer is "yes it is possible" - but in your case the answer is "that is not a Faraday cage". Radio waves are (partially) reflected by any discontinuity in dielectric constant of the medium they propagate through. The ones that propagate (through walls etc) will also experience attenuation. A faraday cage is a continuous conducting structure ...

16

Just to add to what Floris has said. It is frequent (in the UK) that institutional settings would have toughened glass in windows, particularly in bathrooms, gyms etc. that would have the form of a wire mesh (of order 1cm grid) embedded in the glass. That would do a particularly good job of blocking phone signals that would otherwise penetrate the glass.

6

You're right that the classical idea of radiation emission from an accelerated charge cannot be applied to electrons in orbit around nuclei, and thus they do not emit radiation (unless they're in an exited state and decay to a lower state). The same thing does not apply to the nuclei. As you suspect, they will, over time, lose energy and vibrate less and ...

2

To add a little detail about radiative thermal equilibrium: As atoms at nonzero temperature collide with each other, they do emit electromagnetic radiation, and if they were in an empty universe, they would approach zero temperature. However, since the universe isn't empty, they also absorb electromagnetic radiation coming from all the other atoms around. ...

2

If the WiFi antenna is emitting at 2.4 GHz, you could detect a slight improvement of the signal, but unless the door is solid and very thick, I doubt it will make much difference. If it is emitting at 5 GHz the improvement could be bigger, as the wavelength is reduced and the door appears "bigger" to the electromagnetic wave. Finally, if your antenna uses ...

2

remember that the amplitude is not an amplitude in space, it is an amplitude in the sense of the intensity of the electromagnetic field. The spatial amplitude is given by the wavelenght

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So yes, if you compute the Poynting vector (energy flux density), $\vec E \times \vec H$, for an exponentially decaying evanescent wave, you indeed find zero time-averaged energy flux perpendicular to the reflecting plane. Ask you say, this leads to a conundrum --- how do evanescent waves transfer energy across barriers? For sure, we know they can transfer ...

2

When we are calculating the energy levels of an atom (or anything else) we are generally solving the Schrodinger equation to calculate the energy eigenstates. These eigenstates have the property that they are time independant i.e. they do not change with time. So if you consider the ground state and an excited state we end up with the surprising result that ...

1

Intuitively, it is merely energy. It is transmitted by photons. This can take many forms depending on the size of the wave the photon travels upon.

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I think we can think of this as a wave although a bit different from water waves or sound waves.. I hope you agree that wave has energy .afterall by propagating waves energy is transferred..when we think of waves in a medium we can plot the displacement of different points in space and that's how wave propagates. Now in this case (em radiation) the amplitude ...

1

This is mostly because we're usually more interested in the spatial part of a plane wave than in the temporal part, so that plane waves are most convenient when written as $$e^{i(\mathbf k\cdot\mathbf r-\omega t)}. \tag 1$$ The normalization follows from this choice. In general terms, it's hard to call which factor has more weight. There are plenty of ...

1

A key to understanding this is realizing that it's not always true. In fact, at x-ray frequencies, refractive indices are typically less than 1, so that the phase velocity is faster than the vacuum speed of light. The key difference is that x-ray frequencies are well above the natural frequencies of most of the electronic excitations that are involved in the ...

1

Actually the human body emits more than thermal radiation. The Czech military did a study on measuring the extreme low frequency radio band emitted by the nervous system. It can be found on www.measurement.sk by searching Human electromagnetic emission in the ELF band - Measurement ... www.measurement.sk › Lipkova This makes perfect sense when you consider ...

1

This is something I never really understood, but Glen Knoll Offers the following in pp. 116 of his book "Radiation Detection and Measurement": "The energy resolution of the detector is conventionally defied as the FWHM divided by the location of the peak centroid H_0 The energy resolution R is thus a dimensionless fraction conventionally expressed as a ...

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