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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) ?

David Z
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2 Answers2

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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.

anna v
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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.

HolgerFiedler
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