General > General Technical Chat
Veritasium "How Electricity Actually Works"
aetherist:
--- Quote from: electrodacus on May 08, 2022, 12:42:26 am ---
--- Quote from: aetherist on May 08, 2022, 12:22:31 am ---If the gap is small then nonetheless the capacitor sits in the middle of a 1000 mm long short, & the speed of electricity is c/1 in the short, hence LTSpice should still give at least 3.3 ns.
And, if modelled correctly, LTSpice should give the funny rise & the funny falling plateau.
Re the switch, this might be a capacitor, but before it is closed the circuit is in steady state.
--- End quote ---
A capacitor with a 1000mm gap between plates will require 3.3ns and one with 1mm gap will require 3.3ps
LTspice as far as I know has no option to specify the gap between plates and all comercial capacitors even the very high voltage ones will typically have much less than 1mm gap as the smaller the gap the larger the capacity.
So there is nothing strange or not understood about that 3.3ns.
When you close the switch exactly at that contact interface one electron will move from one side of the switch to the other and if a capacitor is in series in the loop as is the case in Derek's experiment then it takes 3.3ns for an electron on the other side of the 1m thick dielectric (air) to feel the effect and vacate a space.
In the battery the space is much smaller so when switch is closed and one electron moves on the other side of the switch the electron wave will travel in to battery say maybe 100mm from the switch then inside the battery the gap say is 1mm and so that electron that left from battery to switch will cause an electron from the wire connected on the other side of the battery to be accepted in the battery and so if total distance is 101mm in a straight line it may take as little as 0.33ns but likely it can not capacitively couple in straight line so it will be an ark maybe say 150mm so around 0.50ns then both sides are coupled at the same time with the wire above that is at about 1m thus 3.3nm + 0.5ns will be the total time from closing the switch until the first packet of energy is transferred from battery to the capacitor (transmission line is a capacitor) and since the lamp is in series between this two 1m capacitors all current used to charge the capacitor also will go through the lamp and be lost as heat and maybe photos.
--- End quote ---
Surely LTSpice is told the distance tween wires, ie 1000 mm. And the small gap tween plates can be ignored.
In which case LTSpice should be able to model the initial transient delay & rise & plateau.
electrodacus:
--- Quote from: aetherist on May 08, 2022, 12:56:27 am ---
--- Quote from: electrodacus on May 08, 2022, 12:42:26 am ---
--- Quote from: aetherist on May 08, 2022, 12:22:31 am ---If the gap is small then nonetheless the capacitor sits in the middle of a 1000 mm long short, & the speed of electricity is c/1 in the short, hence LTSpice should still give at least 3.3 ns.
And, if modelled correctly, LTSpice should give the funny rise & the funny falling plateau.
Re the switch, this might be a capacitor, but before it is closed the circuit is in steady state.
--- End quote ---
A capacitor with a 1000mm gap between plates will require 3.3ns and one with 1mm gap will require 3.3ps
LTspice as far as I know has no option to specify the gap between plates and all comercial capacitors even the very high voltage ones will typically have much less than 1mm gap as the smaller the gap the larger the capacity.
So there is nothing strange or not understood about that 3.3ns.
When you close the switch exactly at that contact interface one electron will move from one side of the switch to the other and if a capacitor is in series in the loop as is the case in Derek's experiment then it takes 3.3ns for an electron on the other side of the 1m thick dielectric (air) to feel the effect and vacate a space.
In the battery the space is much smaller so when switch is closed and one electron moves on the other side of the switch the electron wave will travel in to battery say maybe 100mm from the switch then inside the battery the gap say is 1mm and so that electron that left from battery to switch will cause an electron from the wire connected on the other side of the battery to be accepted in the battery and so if total distance is 101mm in a straight line it may take as little as 0.33ns but likely it can not capacitively couple in straight line so it will be an ark maybe say 150mm so around 0.50ns then both sides are coupled at the same time with the wire above that is at about 1m thus 3.3nm + 0.5ns will be the total time from closing the switch until the first packet of energy is transferred from battery to the capacitor (transmission line is a capacitor) and since the lamp is in series between this two 1m capacitors all current used to charge the capacitor also will go through the lamp and be lost as heat and maybe photos.
--- End quote ---
Surely LTSpice is told the distance tween wires, ie 1000 mm. And the small gap tween plates can be ignored.
In which case LTSpice should be able to model the initial transient delay & rise & plateau.
--- End quote ---
Spice is not the sort of simulation you are imagining. The transmission line is done by adding a bunch of inductors and capacitors together to simulate those two wires.
And as mentioned that 3.3 or so ns delay at the beginning is irrelevant. I can add that delay but it will make no difference.
What you need to understand is that two parallel wires are a capacitor thus an energy storage device.
If you leave the ends open (the 1m pipes that connects the two parallel 10m pipes) the you will still have this first 65ns current through the lamp/resistor as the capacitor's one on each side will be charged but once they are charged you no longer have any current unless you reverse the battery polarity so that you discharge those capacitors and charge them in the other direction then it will again stop.
So energy flows in and out of capacitors and not through capacitors. Energy flows in to capacitor is the key as that energy is not doing work it is stored and just because wires have resistance and a lamp is in series it means that charging is not efficient so not all energy from the source will end up in capacitor as some will be lost to power the lamp/heat the resistor.
hamster_nz:
--- Quote from: SandyCox on May 07, 2022, 10:23:09 am ---Now let's consider the analogy of a spaceship returning to earth. It has both kinetic energy and gravitational potential energy. Both are converted to thermal energy as it reenters the atmosphere. So what carries the gravitational potential energy? Is it the spaceship or the Earth's gravitational field?
--- End quote ---
Gravitational potential energy is the additional energy the spaceship would gain if it were to travel a path between the two points used as the references.
It is not 'carried', it is transferred from the field as it makes the journey though the field.
electrodacus:
--- Quote from: hamster_nz on May 08, 2022, 01:12:11 am ---
--- Quote from: SandyCox on May 07, 2022, 10:23:09 am ---Now let's consider the analogy of a spaceship returning to earth. It has both kinetic energy and gravitational potential energy. Both are converted to thermal energy as it reenters the atmosphere. So what carries the gravitational potential energy? Is it the spaceship or the Earth's gravitational field?
--- End quote ---
Gravitational potential energy is the additional energy the spaceship would gain if it were to travel a path between the two points used as the references.
It is not 'carried', it is transferred from the field as it makes the journey though the field.
--- End quote ---
This seems to be getting out of subject but here is an explanation:
Have you seen the Einstein's explanation of gravity ?
It shows a straight fabric and when an object with mass is added it creates a valley
Now any other object with mass near the planet like the spaceship will also bend that fabric based on spaceship weight thus both planet and spaceship will slide closer to each other.
If there is no mass there is no gravitational field and similarly if there is no electron imbalance there is no electric field.
IanB:
This picture is widely understood to be an analogy. It does not represent what really happens, it is only a pictorial simplification.
The complication here is that general relativity indicates that you can have gravity without mass, and an internal observer experiencing such gravity cannot tell whether the experienced gravitational field is due to mass or otherwise.
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