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| Veritasium "How Electricity Actually Works" |
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| electrodacus:
--- Quote from: rfeecs on May 23, 2022, 05:41:05 pm ---You need the wires to guide the energy from the source to the load. For the case of the battery powering the light, there is very little potential drop along the good conductor wires, so they set up the potential across the load. The power dissipated in the load is VI. For DC, based on conservation of charge, the current has to be the same everywhere in the circuit. So the wires are also needed to provide a circuit for current to flow. This is why you need the wires for DC. It says nothing about where the energy is "flowing". Based on conservation of energy, it flows out of the volume of space surrounding the battery and into the volume of space surrounding the load. The energy flow could be inside the wires or through the empty space. For AC it's a slightly different story. --- End quote --- There is no difference between AC and DC in the sense that energy travels through wires. Else why will you invest in massive transmission lines for AC. In a battery ions are involved so is maybe best to use a charged capacitor as the energy source to better understand what happens. The capacitor plates are basically wires and you have excess of electrons in one plate and deficit of electrons on the other plate. If you connect a wire between the two capacitor plates you allow the electrons to travel from the plate with excess of electrons to the plate with deficit so that they both become neutral as stored energy is discharged. That flow of electrons is electrical current and the density of excess electrons is the electrical potential (voltage). The product of this two is electrical power and the integral of electrical power over time is electrical energy. Since you can not have electron flow outside wires so no electrical current you can not have energy flow outside wires. Let me know what part of my explanation you think is wrong. |
| rfeecs:
What can we actually measure? We can measure fields based on what they do to charges. We can make tiny power sensors with resistors and thermistors for example and measure what happens to them when we position them at a point in space. If they get hot, we can say there is energy at that point in space. So we can develop a theory based on the concept that there is an electromagnetic energy density at any given point in space, based on how much energy is required to move charges or currents to this point in space from infinity. We can calculate what this energy density would be based on the E and B field. We can measure it with the thermistor power sensor or something similar and convince ourselves that the measurements agree with the theory. Based on this theory and the definition of electromagnetic energy density, we can measure energy outside of a wire conducting a time varying current. Similarly, we can measure energy in the empty space of a waveguide. We can measure the energy of a radio signal in free space. We can extend this to a theory of the "flow" of electromagnetic energy and verify it by measurement. For a wire carrying a DC current it's a slightly different story. |
| electrodacus:
--- Quote from: HuronKing on May 23, 2022, 06:04:07 pm --- You still don't get the point of the experiment? To demonstrate the radiation of energy during a transient getting there faster than it could traveling through the wire alone which means some energy was radiated from the switch to the lamp. Ben Watson's simulation demonstrates this explicitly. I'm pretty sure the people who designed HFSS know about electrons... :-DD :-DD :-DD --- End quote --- You made no mention about energy storage ? Do you understand that two parallel conductors are a capacitor? and that a capacitor is an energy storage device? Have you see the Spice simulation I made for a transmission line where I turn the switch ON for just 30ns then turn it OFF The green graph is the power provided by the battery and with magenta power dissipated by the lamp/resistor. How come total energy provided by battery exactly matches the energy arriving at the lamp (most of it quite some time after the switch was OFF) and the delta in energy is found as heat loss in the wire. |
| Naej:
--- Quote from: HuronKing on May 23, 2022, 05:34:38 pm ---The 'energy always travels in wires' people cannot hope to design, let alone explain, how a high-frequency waveguide works and how to CONTROL where energy is going. --- End quote --- It's in the conductor, and follows the conductor. And if you put holes, you'll start radiating the energy. Can the 'energy always travels in vacuum' people explain why you need conductors in waveguides? (in dielectrics, you have polarization current instead of current) Or, since waveguides are wires, in circuits? |
| IanB:
I think one simple (or simplified) way to look at things is that delivered power is the product of voltage and current. The voltage comes from the E field. A strong E field can be propagated by wires and can give a large power delivery, but it has to travel the length of the wires to arrive. A weaker E field can be propagated across the air gap and can give a much smaller power delivery, but it can arrive faster. This qualitatively aligns with Derek's experiment. |
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