General > General Technical Chat
Veritasium "How Electricity Actually Works"
electrodacus:
--- Quote from: snarkysparky on May 06, 2022, 01:04:15 pm ---
Yes it will. It's called the displacement current.
Displacement current is "flowing" anywhere , even in an insulator , where the electric field is varying with time.
https://en.wikipedia.org/wiki/Displacement_current
--- End quote ---
This is the part you are referring to
"In physical materials (as opposed to vacuum), there is also a contribution from the slight motion of charges bound in atoms, called dielectric polarization."
We do not consider the limitations of dielectrics here as there is no such thing as a perfect dielectric but I'm fairly certain that Tim or you do not have the equipment to measure such small losses due to dielectric polarization.
And all examples where 3 to 20V with distance between the plates of 1m in air. Plus that energy is not flowing from one plate to the other of the capacitor. That is lost energy in the form of heat in the dielectric (air in case of a transmission line). This is insignificant compared to IR radiation from the wires and that IR also will not transfer any energy to the load unless you say that an IR photon will help a bit the filament of a lamp but will sure not charge a discharged capacitor.
When you charge a capacitor the energy remains in the capacitor (except for the one ending up as heat due to capacitor plate resistance) so energy did not flow trough the capacitor so trough dielectric on the other side but remained stored so that if you disconnect the capacitor and apply a load (say a resistor or lamp) you can get that energy out.
bsfeechannel:
--- Quote from: Naej on May 06, 2022, 12:49:50 pm ---Yes, this is how the hydraulic analogy is inaccurate. Which is why the word 'analogy' is used: it's very similar, not identical.
--- End quote ---
But it is brain-damaging engineers. It's time to get rid of it.
--- Quote ---The energy arrives 1m/c where c is the speed of sound in air.
--- End quote ---
But not in vacuum.
--- Quote ---For the same reason: opening the valve emits a sound wave, because you're violently compressing/accelerating water.
Just as in the experiment proposed, it's a tiny amount of energy.
--- End quote ---
The amount of energy is irrelevant. What you are not paying attention is that the energy that arrives first through space is not a spike of energy. It is a sustained continuous step and it does not disappear. When the rest of the energy flowing through space guided by the wires finally arrives, it is just added to the initial step.
Comparing Derek's and Alpha Phoenix's setup, you'll see that the step "duration" is proportional to the length of the line. If it were 300km, it would "last" 1s. If it were infinite, it would last as much as you'd want. So, it is not a "transient", it is "standient", that doesn't go away.
Another problem is that some people who do not accept that the energy flows through space, are prepared to understand that the Poynting vector, perpendicular to the surface of the load, really conveys the energy that it will dissipate. But they don't understand that the wires are also resistors, and that the Poynting vector, perpendicular to whatever surface of the wire, be it radial or axial, will cause that energy to be dissipated by the wire.
In other words, you cannot hand energy to a wire in one side and expect that this energy will reappear at the other side. The wire will dissipate it entirely.
You can prove that by connecting any piece of wire to the poles of a battery. The energy will not be transferred from the negative pole to the positive pole. It'll simply be dissipated. Completely.
Sounds ridiculous, but people do not connect the dots.
snarkysparky:
dielectric polarization is not about losses. It is about the atoms in the dielectric having a polar electrostatic potential and in the presence of an electric field they mostly rotate to line up with
that field thereby strengthening the field.
Energy absolutely does flow through a capacitor.
https://en.wikipedia.org/wiki/Capacitive_power_supply
TimFox:
Just to annoy those who dislike complex values, the dielectric "constant" or permittivity of material due to internal polarization with applied electric field is represented by a complex frequency-dependent value to include dielectric loss.
See: https://en.wikipedia.org/wiki/Permittivity for a detailed explanation.
The relationship with dielectric loss is discussed in https://en.wikipedia.org/wiki/Dielectric_loss
As is well known, the dielectric loss of typical insulators at reasonable frequencies is measurable: good plastics such as polypropylene have dielectric loss around 0.1%, but polyester (Mylar) is roughly 1%. PVC is much worse.
My anecdote (already posted here several times) about the late Professor U Fano (at the University of Chicago) lecturing on dielectric phenomena was about a quantum-mechanical calculation of the polarization in a medium with harmonically-bound electrons.
electrodacus:
--- Quote from: snarkysparky on May 06, 2022, 04:13:50 pm ---dielectric polarization is not about losses. It is about the atoms in the dielectric having a polar electrostatic potential and in the presence of an electric field they mostly rotate to line up with
that field thereby strengthening the field.
Energy absolutely does flow through a capacitor.
https://en.wikipedia.org/wiki/Capacitive_power_supply
--- End quote ---
If energy does not flow trough a capacitor then it can only flow trough wire.
So what are we disagreeing on ?
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version