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[#1]

So fibre can carry hundreds of signals / streams at once. More signals = more throughput. But so can electrical - just look at your cable tv connection - 200+ channels, and all sent over the one wire. It's the same principle - different frequencies on the radio dial. Fibre uses the same principle, and can carry 100+ channels, but the frequencies are represented by different colours, split and combined using a prism - though you cant see these colours as they're deep into the infra-red (like how you cant see the light from your TV IR remote). The main difference is that electrical has a limit to how much total combined speed it can carry...

Let's look more at the differences between spanish online classes electrical and fibre signals.

Electric cables are susceptible to noise - think about if your mobile phone is near a speaker and you get the buzzing. Lots of things aside from your phone can give out this interference - power lines, other cables in the same duct, TV/Radio stations, even radio hiss from space! Now imagine that over a looong cable between two cities and you're talking about a lot of noise on the signal (like radio static on a weak station). Even shielding them only reduces the noise to a certain extent. As well as receiving noise, electrical cables radiate signals - they are like a long antenna, some of the signal gets radiated and lost this way so it gets weaker.

Fibre signals aren't susceptible to noise - a solid black tube can't pass any light at all, so the fibres within the cladding are completely blacked out from external light. (Note there can be reeealy tiny amounts of noise from quantum effects and the electronics at each end, but its minuscule compared to electrical.) The light within the also doesnt leak out. Refraction is like a near-perfect mirror, keeping the signal bouncing inside the fibre for a very long distance.

So we've established that electrical signals get noisy, and fibre optics don't pick up interference.

Next, we have signal degradation.

Electricity has "inductance" - this manifests itself very similarly to physical inertia, which means it resists being changed. Heavier objects are harder to move and stop than lighter ones. So electricity has the same thing, it takes time to change the signal - which is what happens when the zero and one bits are transmitted. The longer the cable, the more the inductance (i.e "inertia"), so the longer it takes to change that zero to a one. Therefore you have to send signals at a slower rate to allow the electrons to keep up with the changes. There is a similar related effect called capacitance which also slows down the maximum rate of change.

Light has no inductance, (so there is effectively no "inertia") - therefore changing it from zero to one is pretty much instant. That means you can change it much faster - more "bits per second" - regardless of distance.

(note it's not really "inertia", the above is mostly an analogy, but it behaves like it)

Next is resistance. Electrons are large (compared to photons), so they interact with the copper atoms as they travel through the wire. This interaction is analogous to friction. Friction creates heat, which is where the energy goes. In a wire, some electrons lose energy in the same way as heat (which is why power cables can get hot when carrying a lot of current). So over a long distance, much of the signal diminishes due to resistance. For high speed signals (1-10Gbps), this typically happens within a few hundred metres. Not very useful when you need to get cat videos between cities!

[#2]

🌼 🌼 🌼   Bonjour  🌼 🌼 🌼  @rino13     🌼  

Ton post sans aucune courtoisie s'apparente à un vent bien sonore en plein milieu d'un repas de fête.

Il ne pose aucune question, il ne répond à aucune question et il énonce au moins une contre vérité.

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@rino13  a écrit :

Light has no inductance, (so there is effectively no "inertia") - therefore changing it from zero to one is pretty much instant. That means you can change it much faster - more "bits per second" - regardless of distance.

(note it's not really "inertia", the above is mostly an analogy, but it behaves like it)

Maxwell et Schrödinger se retournent dans leurs tombes à la lecteur de ce texte.

As-tu déjà entendu parler de la "vitesse de groupe".

C'est la conséquence de la propagation des ondes électromagnétiques dans un support.

La différence principale entre fibre et cuivre est la fréquence des ondes électromagnétiques, mais dans les deux cas le phénomène est régi par les mêmes équations et certains termes ont des poids différents selon qu'on est en électricité ou en optique physique.

Les lois de la propagation de la lumière dans une fibre en limitent la longueur.

Comme pour le téléphone, il faut des répéteurs avant que le signal perde toute signification, sinon, il y a lurette qu'il y aurait des fibres directes et continues de Cadix à Vladivostok, ou d'Anchorage à Valparaiso

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@rino13  a écrit :

So we've established that electrical signals get noisy, and fibre optics don't pick up interference.

Et c'est qui ce "nous"  qui vient d'enfoncer une porte ouverte ?

Oui les ondes électriques se déforment

Exactement comme les vagues au tour du caillou qui tombe au milieu du lac s'atténuent avant de toucher les berges, comme le bruit de l'avion diminue quand il s'éloigne., ....

Pourquoi ce cours de mécanique ondulatoire ici ?

Je t'invite à suspendre un poids au bout d'un ressort.

Tu tires le poids vers le bas de quelques cm et tu le laches.

Analyse son mouvement et tu retrouveras encore et encore les mêmes équations.

"Le ressort, il n'y a que cas de vrai  !"

Gandi (Paris  15 ) 1971

Cordialement

PhilDur