Wikipedia says that

Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. The oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave.

The page also includes this image:

electromagnetic wave

which shows that.

But I find that sometimes the wave is represented with B-field at is peak on the nodes, like here:

Alternate picture of wave with fields out of phase

taken from Wikimedia Commons, and it would make some sense, too, considering that it grows with acceleration and this is maximal there.

Can you please say if the second picture is wrong, and if those representations are both a mere pictorial, fictional, simplified, arbitrary representation of an EM wave?

Do you know if modern instruments are able to record with precision the oscillations of the electric and magnetic field when detecting photons (now we have lots of collimated photons in laser beams can you detect the fiels at the emittter or receiver) ?


marked as duplicate by garyp, heather, ACuriousMind, user36790, knzhou Aug 22 '16 at 4:52

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ Voting to reopen, as the question in the last sentence is not addressed in the cited duplicate. $\endgroup$ – garyp Aug 22 '16 at 12:47
  • $\begingroup$ I'm going to create a new question focusing on the experimental evidence. $\endgroup$ – garyp Aug 22 '16 at 13:01
  • $\begingroup$ Just making a note in response to some now-deleted comments that failure to cite and quote copied material is never okay, regardless of the quality of the source. $\endgroup$ – David Z Aug 22 '16 at 14:21
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    $\begingroup$ @garyp Indeed the final sentence poses a non-duplicate question, but unfortunately the main problem here is that the post asks multiple questions. So, part of it is a duplicate and part is not. OP should edit the post down to a single focused question. $\endgroup$ – DanielSank Aug 28 '16 at 23:10
  • $\begingroup$ @DanielSank, why multiple question? is laser not light? the question is one, and then there is the request to support the answer with experimental evidence $\endgroup$ – user104372 Aug 29 '16 at 4:39

The shift of 90° between the maximum of the electric field component to the magnetic field component is a very natural view on how photons are propagating in free space. First this is the situation in the near field of an antenna radiation. An electric field induces a magnetic field induces again a magnetic field and so on. Second this shift conserves the energy content of the photon in any point of it's movement in space.

The derivation of the sin is a cos is a -sin is a -cos and perhaps it is possible to transform Maxwells equations in such a way, isn't it?

Perhaps it is possible to interprete in the far field of the radio waves as no shifted by 90° but my question about measurement results for such a interpretation does not get any source to this measurements.

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    $\begingroup$ I don't think this answers the question. Also, note that the phase shift has nothing to do with conservation of energy. Energy is conserved when there is a phase shift (near the antenna) and when there is no phase shift (far away from the antenna). Note also that using the language of photons and the language of fields at the same time leads to a confused picture. $\endgroup$ – garyp Aug 21 '16 at 11:59
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    $\begingroup$ @garyp It seems to be a mantra that in the far field of a radio wave there is no shift since it was never measured, see your own comment. And how we can learn something about photons if not from the behaviour of radio waves there a huge number of photons get emitted from accelerated electrons? The appearing fields are made from this photons and this is why we know that each photon has varying electric and magnetic field components. $\endgroup$ – HolgerFiedler Aug 21 '16 at 12:05
  • $\begingroup$ @garyp And about what are photons, what is EM radiation and what are radio waves I expressed myself very clear here $\endgroup$ – HolgerFiedler Aug 21 '16 at 12:09
  • $\begingroup$ The E and B fields of radio waves can be measured, and in the far field they are in phase. There is no difference between the behavior of optical waves and radio waves. Fields are not made of photons. Photons are excitations of fields. The fields exist whether or not there are any photons in them. $\endgroup$ – garyp Aug 21 '16 at 12:10
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    $\begingroup$ @garyp please give a source for the measurement of the far field components and it's shift or no-shift of radio waves. $\endgroup$ – HolgerFiedler Aug 21 '16 at 12:16

Radiation from the sun follows a black body spectrum more or less, and is not coherent, i.e. the phases between different slices of sunlight are not defined. The photons come from innumerable incoherent de-excitations from the plasma of the sun's surface.

It can be simulated by plane waves impinging at all the frequencies of its black body spectrum, which is your first plot. Those functions describe plane waves.

Incoherent electromagnetic waves can be made coherent when passed through small openings, a slit for example, that is why interference fringes appear at single slits. The appearance of fringes validates experimentally the plane wave functions describing the electromagnetic wave.

Do you know if modern instruments are able to record with precision the oscillations of the electric and magnetic field when detecting a photon?

The photon is a quantum mechanical elementary particle, and classical beams and their electric and magnetic fields emerge from a superposition of innumerable photons.

Photons when detected individually are a single point on a screen , leaving energy h*nu where nu is the frequency of the classical beam that was built up by such photons, and at most one can detect in its interactions the spin it has, +/-h in its direction of motion. No electric or magnetic fields, because the information about them is carried in the wavefunction describing the photon which is a complex function and cannot be susceptible to measurement. Only in the confluence of innumerable photons one reaches the classical regime where electric and magnetic fields can be detected. Yes, there are antennas which detect and measure electric fields from the electromagnetic radiation.

  • $\begingroup$ laser light is coherent hyperphysics.phy-astr.gsu.edu/hbase/optmod/lascon.html . I do not think people bother with the magnetic field of an incoming electromagnetic wave. The electric field is what is caught at the antennas and registered. $\endgroup$ – anna v Aug 21 '16 at 19:55
  • $\begingroup$ anna, the electric field caught at the antenna is not the field of the photons, (is it? ) but the field caused by them making the electron in the antenna oscillate. It is therefore obvious that that E-field is synchronous with the incoming B-field of the radiation. Don't you agreee they have it all mixed up? $\endgroup$ – user104372 Aug 22 '16 at 4:34
  • $\begingroup$ It is not the electric field of the photons. The electric field of the photon is in a complex number form in the wavefuncion. The interactions of photons always happen with the square of the wavefunction, so the electric field of a photon is not a measurable quantity. The antena picks up the field built up by the zillions of photons in the wave. The coherence of the laser light is a coherence in the electric field waveform. This phase can will be mathematically found in the complex phases of the wavefunction but is not measurable. only the confluence/supeposition of photons is measurable $\endgroup$ – anna v Aug 22 '16 at 5:24
  • $\begingroup$ As far as photons go, the phases is seen only in the built up probability density distribution. This mathematically coincides with the energy distribution of the classical wave, because both the classical and the quantum form come from maxwell's equation, for photons used as operators on the wavefunction. arxiv.org/ftp/quant-ph/papers/0604/0604169.pdf $\endgroup$ – anna v Aug 22 '16 at 5:26
  • $\begingroup$ Am I missing something, or are you actually saying that the fields and consequently their phases have never and can never be detected, and we must believe in their syncronicity as an act of faith to Maxwell's theory? $\endgroup$ – user104372 Aug 22 '16 at 8:56