Electricity doesn't work the way I thought it did
Discussion
speedy_thrills said:
speedy_thrills said:
The Poynting vector describes the flow of energy through a static EM field but the description in the video is not correct because the question is about a dynamic system (you are flipping the switch.) This is an electrodynamics problem and that means you need an equation that includes a "t" for time and, as you may have noticed, the pointing vector does not have a time variable.
Someone sent me this video today and it's a far better visual demonstration of what actually happens when you flip the switch on a circuit:https://youtu.be/2AXv49dDQJw?si=nxD0aQEJimEvgl7Q
I'd rather not be but I have such basic questions when anyone (or a video) seeks to enlighten me that either: must infuriate the teacher and they give up or the video doesn't answer.
Yet, I managed to follow that video.
Brilliant explanantion and demonstration.
Nice find, S_T!
dukeboy749r said:
speedy_thrills said:
speedy_thrills said:
The Poynting vector describes the flow of energy through a static EM field but the description in the video is not correct because the question is about a dynamic system (you are flipping the switch.) This is an electrodynamics problem and that means you need an equation that includes a "t" for time and, as you may have noticed, the pointing vector does not have a time variable.
Someone sent me this video today and it's a far better visual demonstration of what actually happens when you flip the switch on a circuit:https://youtu.be/2AXv49dDQJw?si=nxD0aQEJimEvgl7Q
I'd rather not be but I have such basic questions when anyone (or a video) seeks to enlighten me that either: must infuriate the teacher and they give up or the video doesn't answer.
Yet, I managed to follow that video.
Brilliant explanantion and demonstration.
Nice find, S_T!
Yes, sometimes finding someone explaining something only slightly differently, can be the difference between continued ignorance or a 'light bulb' moment. Well, for me at least.
Plus, you get variations on a theme and more fullsome explanations/debates, which is helpful.
All great stuff.
Plus, you get variations on a theme and more fullsome explanations/debates, which is helpful.
All great stuff.
The battery has a relatively high impedance, so faced with a (near) short circuit, the voltage will decrease practically to zero almost immediately.
It would be interesting to see the same demonstration with a high current power supply (only needs to be a few mV to avoid melting the wires), to see if the same theory applies - i.e. without the subsequent drop in voltage from the battery - would we still see the same effect given that the voltage / current will be sustained?
In the case of the demonstration in the video, as the voltage is applied a small magnetic field is generated which then promptly collapses as the battery is unable to maintain sufficient current to keep the circuit energised.
It would be interesting to see the same demonstration with a high current power supply (only needs to be a few mV to avoid melting the wires), to see if the same theory applies - i.e. without the subsequent drop in voltage from the battery - would we still see the same effect given that the voltage / current will be sustained?
In the case of the demonstration in the video, as the voltage is applied a small magnetic field is generated which then promptly collapses as the battery is unable to maintain sufficient current to keep the circuit energised.
The thing I like about this explanation is that it gets you a lot further in a very intuitive way. You now understand that electromagnetic fields are set up, they aren't just instantaneously willed into existence and that you get propagation even in dead legs.
It also gets you down the road to start thinking about concepts like the capacitive nature of grids and inductive or resistive nature of circuit loading and why it might matter.
It also gets you down the road to start thinking about concepts like the capacitive nature of grids and inductive or resistive nature of circuit loading and why it might matter.
Edited by speedy_thrills on Wednesday 22 May 10:18
speedy_thrills said:
Someone sent me this video today and it's a far better visual demonstration of what actually happens when you flip the switch on a circuit:
https://youtu.be/2AXv49dDQJw?si=nxD0aQEJimEvgl7Q
Thanks for posting that, really enjoyed it. Hope that bloke is teaching outside you tube as well, given his obvious talent for it.https://youtu.be/2AXv49dDQJw?si=nxD0aQEJimEvgl7Q
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