0
$\begingroup$

So from what I know I think that the magnetic and electric fields around the antennas move away from the antennas because the vectors in the magnetic and electric field have direction and strength so the photons hanging around the antemna will get pushed in the direction of the vector. Am I correct, if not please tell me what I did wrong and what the right answer is.

Thanks, Gary

$\endgroup$
2
$\begingroup$

You keep asking the same question, so maybe one has to start at the beginning.

brems

Bremsstrahlung produced by a high-energy electron deflected in the electric field of an atomic nucleus

The electric field of the nucleus is very strong, and the deflection of the electron generates a photon which flies off with velocity c, and the electron departs with smaller energy. If it meets another nucleus , it will degrade in energy by emitting another photon again. The fields of the atoms are very strong, and the photons leaving the interaction are of X ray frequencies. The whole process can be calculated quantum mechanically giving the probabilities of such radiation happening.

This is a general phenomenon for all electron energies: If the electron is decelerated by entering some electric field region, it will emit the photon, if it is accelerated the same will happen, a process that is also in the equations of classical electromagnetic theory, except there the mathematics gives an electromagnetic wave, where the energy leaving has a sinusoidal form.

An antenna is a geometrical shape that uses conductors. Conductors have a conduction band, where the electrons are practically free of the atoms and can be moved , accelerated and decelerated with applied electric fields. The energies used are very much lower than in in the production of X-rays, but the logic is the same: acceleration and deceleration of electrons forces photons to be emitted.

antenna

This is done by the current carrying circuits in the antenna circuit. At the electron level the acceleration and deceleration imposed with the period of the current of the circuit, forces individual electrons to emit a photon at an angle to the field, depending their motion and the momenta involved.

There are order of 10^23 electrons dancing in tune in the antenna, and thus an enormous number of photons in synchrony are generated leaving immediately (BUT continuously) in synchrony with the signal imposed by the currents of the circuits.

The superposition of all these photons creates the electromagnetic wave, in this example the radio wave, building up the electric field of the classical wavewave ( the magnetic is perpendicular to the electric). Each photon leaves with velocity c, but there are so many that the classical wave appears continuous.

Here is a graph as an example of how photons add up to the classical wave that may help.

photspin

The electric field of the electromagnetic wave is the red arrow, the magnetic will be perpendicular to it and the direction axis.

$\endgroup$
  • $\begingroup$ Anna Greatful. Perhaps I'm penetrating but how do you think, are the emitted photons of the wavelength of the radio wave? Or is the radio wave simply a modulated by the antenna generator EM radiation? $\endgroup$ – HolgerFiedler Mar 3 '17 at 14:19
  • $\begingroup$ The variable V in the antenna graph, changes the number of electrons accelerating and decelerating and thus the number of photons produced. The sinusoidal V shapes are transferred to the photons and the emergent classical wave . do not forget that it is the E that characterizes the energy of the classical em wave, fewer photons, smaller E built up. $\endgroup$ – anna v Mar 3 '17 at 15:40
  • $\begingroup$ What I wanted to point out is that the graphics showing the EM spectra is mixing the possible spectra from excited atoms and molecules (thermic radiation, Bremsstrahlung and so on) and the modulated radiation (radio waves). The first radiation goes from gamma to infrared and perhaps to microwave and the H-line and the second depends only from the capabilities of the wave generators, be this a radio wave generator or a rotating star. $\endgroup$ – HolgerFiedler Mar 4 '17 at 5:40
  • $\begingroup$ (s)As you said "forces individual electrons to emit (individual) a photon". The second individual is from me to underline that the radio wave is a composition of photons. And this photons of very different wavelengths and not of the wavelength of the radio wave. $\endgroup$ – HolgerFiedler Mar 4 '17 at 5:44
0
$\begingroup$

No, you're wrong.

Think of a great sheet with a ball moving up and down in the middle. The position and velocity of the ball determines how the sheet behaves around it, but because it is constantly accelerating up and down, the sheet around changes periodically. Furthermore, it takes time until the whole sheet is 'aware' to the balls new position, so the 'rearranging' of the sheet spreads away from the ball. This is a wave.

Now take the same situation, but the ball is the charges in the antenna, the sheet is electric and magnetic fields (which are affected by the charges position and velocity), and when the charges are moving, the electric and magnetic fields rearrange themselves, but it takes time for the information to move - and that is the electromagnetic wave the antenna is creating.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.