When 50,000 volts go through a wire at 5,000,000 FPS - The Slow Mo Guy

[nsaspook]

 

[Drakkith]

Nice!

 

[hutchphd]

Different type of fallout from the Manhatten project. Lots of human mental capital in one location. "What do you mean the timing must be microseconds?" Just another day at the office for those folks.......

 

[sophiecentaur]

I can't see the video.
The title is sensational but do volts 'go through' at a certain speed?

 

[Drakkith]

I believe the 'speed' is referring to the FPS of the camera.

 

[sophiecentaur]

I believe the 'speed' is referring to the FPS of the camera.

I can now see the video and Yes. But 'Volts" and 'Through' rankles a bit. The discharge (=current) goes through. All very well in a fun video but people take that sort of thing into basic electrical problems and it can all go to hell. There are less confusing ways to title a video.

 

[davenn]

But 'Volts" and 'Through' rankles a bit.

Yeah, volts dont go through anything

 

[nsaspook]

I can now see the video and Yes. But 'Volts" and 'Through' rankles a bit. The discharge (=current) goes through. All very well in a fun video but people take that sort of thing into basic electrical problems and it can all go to hell. There are less confusing ways to title a video.

Those that will be confused, will be that way with any video title.

 

[Drakkith]

Yeah, volts dont go through anything

If you spill a bunch of batteries into a stream, are the volts flowing now?

 

[davenn]

If you spill a bunch of batteries into a stream, are the volts flowing now?

depends of if they are light enuf to be carried downstream rather than sink to the bottom

 

[sophiecentaur]

Those that will be confused, will be that way with any video title.

That's a view which can lead to mis-education from the very start. It doesn't excuse the bad title and reflects badly on the presenter.

 

[nsaspook]

That's a view which can lead to mis-education from the very start. It doesn't excuse the bad title and reflects badly on the presenter.

Lost battle. Those that are curious about why, might get educated, those that are not, won't remember the title, only the sparks.

The data is the point, not the phrase.

 

[tech99]

5 M frames per sec is not fast enough to capture the wave that travels down the wire starting from the switch, which takes just about a nanosecond. During the propagation of this wave, which is a wave of compression of the free electrons in the wire, there is a strong electric field having a component acting along the wire, and travelling along it rather like a shock wave. So in a sense the voltage is travelling along the wire.

 

[Guineafowl]

Could it be said that the connecting wires have some velocity factor, eg 0.7, and the electric (electromagnetic?) wavefront travels at 0.7c around the outside of the wire, which acts as a sort of ‘waveguide’?

Would it also help to think of current not as electrons drifting along like little ball bearings, but as quantum ‘things’, jiggling randomly, which acquire a net direction as the wavefront passes?

 

[tech99]

Could it be said that the connecting wires have some velocity factor, eg 0.7, and the electric (electromagnetic?) wavefront travels at 0.7c around the outside of the wire, which acts as a sort of ‘waveguide’?

Would it also help to think of current not as electrons drifting along like little ball bearings, but as quantum ‘things’, jiggling randomly, which acquire a net direction as the wavefront passes?

Where does the initial wavefront come from?

 

[Guineafowl]

Where does the initial wavefront come from?

The terminals of whatever power supply they have?

 

[tech99]

One of these terminals has an excess of electrons on it, waiting to "go". That is the initiation of the wavefront. We require electrons to initiate the electric field of the wavefront.

 

[DaveE]

Could it be said that the connecting wires have some velocity factor, eg 0.7, and the electric (electromagnetic?) wavefront travels at 0.7c around the outside of the wire, which acts as a sort of ‘waveguide’?

Yes, that works for me. But the charges inside the wire (the waveguide part) are also involved. Ultimately it's a bit too complex to be described by simple phrases.

There are some good Veritasium videos about this.

 

[Guineafowl]

One of these terminals has an excess of electrons on it, waiting to "go". That is the initiation of the wavefront. We require electrons to initiate the electric field of the wavefront.

A ‘negative’ wavefront? Does an opposite wavefront travel the other way around the circuit?

Yes, that works for me. But the charges inside the wire (the waveguide part) are also involved. Ultimately it's a bit too complex to be described by simple phrases.

There are some good Veritasium videos about this.

I did see those, and the responses from other channels. Interesting, but no substitute for understanding at the deepest levels, of course. More on the level of Feynman’s ‘fun to imagine’ descriptions. A good start for learning transmission line theory.

Two important points I took away from that:
1. When you rig up the circuit (switch open), you leave enough time for the surface charge to arrange itself, such that the charge imbalance is right across the switch terminals. I assume this happens at near c.

2. The timing of the initial current at the fuse wire/load depends on the straight line distance between the switch and load, regardless of the length of wires.

Does this current pulse fade away, to be replaced by the much larger one travelling along the wire ‘waveguides’?

Since the fuse wire and connecting wires might have different characteristic impedances, are there reflections and ringing going on that can explain what’s seen in the slo-mo video?

 

[tech99]

A ‘negative’ wavefront? Does an opposite wavefront travel the other way around the circuit?

I did see those, and the responses from other channels. Interesting, but no substitute for understanding at the deepest levels, of course. More on the level of Feynman’s ‘fun to imagine’ descriptions. A good start for learning transmission line theory.

Two important points I took away from that:
1. When you rig up the circuit (switch open), you leave enough time for the surface charge to arrange itself, such that the charge imbalance is right across the switch terminals. I assume this happens at near c.

2. The timing of the initial current at the fuse wire/load depends on the straight line distance between the switch and load, regardless of the length of wires.

Does this current pulse fade away, to be replaced by the much larger one travelling along the wire ‘waveguides’?

Since the fuse wire and connecting wires might have different characteristic impedances, are there reflections and ringing going on that can explain what’s seen in the slo-mo video?

2. I do not agree with this statement . The wave follows the wire, as a waveguide, so that if the wire is in a tortuous path, say a helix, the wave will tend to follow round the curves at nearly the speed of light.
3. There are actually two pulses, of opposite polarity, which originate- from the two sides of the switch. If the wire had zero resistance, these waves would circulate for ever. But if the resistance is finite then they gradually die away. The discharge of a capacitor is often of an oscillatory nature. If C is very large, or is perhaps represented by a battery, then the wave may die out before the discharge is complete, so we end up with DC flowing.
4. Changes in the diameter of the wire and its insulation will cause small variations in the characteristic impedance of the waveguide, so that, as you correctly state, reflections and addition ringing will occur.

 

[Guineafowl]

2. I do not agree with this statement . The wave follows the wire, as a waveguide, so that if the wire is in a tortuous path, say a helix, the wave will tend to follow round the curves at nearly the speed of light.

What I said seemed to be the conclusion of Veritasium’s experiment? Time to first current pulse in the bulb was 1m/c seconds, determined by the 1 m straight-line distance from switch to bulb, rather than the 1 second you’d expect as the wires were 1c metres long, assuming a velocity factor of 1.

 

[tech99]

The propagation along a wire will depend on the shape into which it is bent and the proximity to other parts of the wire and other objects. Other modes will be excited in some cases. As Maxwell says: "In the case of electric currents, the resistance to sudden increase or diminution of strength produces effects exactly like those of momentum, but the amount of this momentum depends on the shape of the conductor and the relative position of its different parts." (A Dynamical Theory of the Electromagnetic Field, 1864). I would also mention that the wire constitutes a resonator which is shock excited at its resonant frequency, and it is a characteristic of resonant transmission lines that the phase of the currents and voltages are everywhere the same. So a measurement after the initial impulse will show zero time delay along the wire.