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Old 06-25-2014, 07:11 PM   #21
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It is actually the electromagnetic field that propagates at the speed of light, and you get an emf where ever you get an electric current. If the current is alternating then some of that emf can propagate through the air.
Should you be using language like that on the forum?
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Old 06-25-2014, 07:16 PM   #22
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It is actually the electromagnetic field that propagates at the speed of light...
True.

But how do you explain in simple terms to a layman that despite the low speed of electrons in a wire, when he turns on a switch, his bulb lights up right away? In the example I cited above, the electron's speed is only 14 in/hr, yet his lamp is many feet away from the switch!
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Old 06-25-2014, 07:19 PM   #23
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Thank you NWB for the time and effort... Appreciate that very much. Not sure I'd be that accommodating.

On the Lightning surge... I wonder if my problem might have come... not from the electric supply, but from the Comcast connection... and the Cat5 cables.
Though the computer, which was off at the time, wasn't affected, the Comcast modem, the Vonage Modem, the Sony media player (cat 5 connection) and the hard drive that was connected to the Sony.... My mistake in the post was that the monitor not affected. The Comcast connection is only to the Comcast modem... not to a box or a TV.

My suspicions about the dimmer control are unfounded. Now, I understand Thyristors, and won't beat up on DW for leaving the Overheads dimmed at night.

Again.. appreciate the time and effort... hopefully not too old to learn new tricks.
The surge protectors that you can buy are for power surges caused by fluctuations in the voltages coming from your power supply, which causes lights to dim and brighten etc.

A lightning strike will send a voltage spike through the wires at thousands of volts and if there is not a physical gap then it is going to travel through the circuits. Fiber optics are great for protecting sensitive instrumentation in structures such as chemical plants where you want to minimize the amount of instrumentation damaged during lightning strikes
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Old 06-25-2014, 07:22 PM   #24
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True.

But how do you explain in simple terms to a layman that despite the low speed of electrons in a wire, when he turns on a switch, his bulb lights up right away? In the example I cited above, the electron's speed was only 14 in/hr, yet his lamp is many feet away from the switch!
But, why does the electron move at all since the current is reversing direction 60 times a second?
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Old 06-25-2014, 07:23 PM   #25
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...(snip)...
15. Empirical observation ...I have bought chargers of all kinds for electronic devices... paid $.10 to $.25 each, and now have about 60 different chargers. No correlation that I can see between Volts, Amps and the plug in terminal... plus I don't understand why some chargers with the same output are very small, while others are five times the size.
...
Some of those cheap chargers could be fire hazards. I would be very careful if they did not come with the original equipment.
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Old 06-25-2014, 07:24 PM   #26
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Should you be using language like that on the forum?
Apologies if emf means something other than electromagnetic field or electromotive force. I've only lived in the US for 27 years, I still haven't figured out the language differences
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Old 06-25-2014, 07:26 PM   #27
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But, why does the electron move at all since the current is reversing direction 60 times a second?
In an AC circuit, the electrons wiggle or boogie in place. They have no net motion, but their wiggling speed is still very slow.

If they move 14 in/hr in a 5A DC current, then with a 5A AC current, their peak velocity is still 14 in/hr. And if they have to reverse direction at 60 times/sec, they do not get very far very fast.

But let's go back to just the simple DC current for now, to consider the explanation to our layman how his lamp turns on immediately.
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Old 06-25-2014, 07:35 PM   #28
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Some of those cheap chargers could be fire hazards. I would be very careful if they did not come with the original equipment.
I have bought a couple of USB chargers to use with our iPhones off eBay. I paid $1.99 for a kit containing 1 wall charger, 1 cigarette plug charger, and 1 USB cable. Shipping from China included.

When I received it, carefully measured the output voltage to make sure it was 5V to avoid blowing up the phone. It looked OK. I have used them for a few months. They look just like the after-market chargers I have seen for a lot more money, those white 1" cubes you plug into a wall outlet.
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Old 06-25-2014, 07:44 PM   #29
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His lamp turns on instantly because the electron's electric field propagates through the wire at a significant fraction of the speed of light. It causes the electrons in the filament in the lightbulb to instantly move in response.

It is similar to what happens on the water when a boat passes by 100 feet away from your boat. If you were to dye a section of the water near the boat and watch it, you would see that the water actually doesn't move very far and yet a few seconds later the water near you moves and your boat moves. Since it takes energy to move your boat, that energy has been transmitted by the wave moving in the water, just like the energy is transmitted by the electric field moving in the wire. The water molecules are like the electrons. They both just slosh around a bit and don't really move very far very fast.
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Old 06-25-2014, 07:45 PM   #30
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... in a copper wire of cross-section 0.5 mm2, carrying a current of 5 A, the drift velocity of the electrons is on the order of a millimetre per second...

That's 3.6 m/hr or 14 in/hr.
Talk about inflation! Back when I was a kid, 3.6m/hr equaled 142 in/hr!
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Old 06-25-2014, 07:50 PM   #31
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But let's go back to just the simple DC current for now, to consider the explanation to our layman how his lamp turns on immediately.
Because the charged particles (electrons) generate an emf that travels down the wire at the speed of light. For a DC circuit the direction of the magnetic field around a wire can be determined using Maxwells right hand corkscrew rule. (the magnetic and electric fields are always at right angles to one another)

The current that travels down a wire is the emf being passed between electrons. (I'll try and avoid terms like excited electrons in case REW reports me for using sexual innuendo). That is the layman's simple explanation, but I was never a teacher, so I'm sure someone like Professor Cox would do a much better job.

For a full explanation you would need to study Maxwell's equations.
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Old 06-25-2014, 07:53 PM   #32
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His lamp turns on instantly because the electron's electric field propagates through the wire at a significant fraction of the speed of light. It causes the electrons in the filament in the lightbulb to instantly move in response.

It is similar to what happens on the water when a boat passes by 100 feet away from your boat. If you were to dye a section of the water near the boat and watch it, you would see that the water actually doesn't move very far and yet a few seconds later the water near you moves and your boat moves. Since it takes energy to move your boat, that energy has been transmitted by the wave moving in the water, just like the energy is transmitted by the electric field moving in the wire. The water molecules are like the electrons. They both just slosh around a bit and don't really move very far very fast.
Perfect
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Old 06-25-2014, 07:57 PM   #33
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+1

Here's another analogy that I would use.

Imagine hooking a long garden hose to a faucet, and that the garden hose is filled with water. The moment you open the faucet, water starts flowing immediately out the other end. The water molecules flowing out of the hose are not the same as the water molecules entering from the faucet.

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...electric field propagates through the wire at a significant fraction of the speed of light...
The electron motion down the wire is started by the electric field propagation in the dielectric material surrounding the wire. The speed of propagation depends on the dielectric constant of the material and is usually a large fraction of the speed of light in vacuum as you noted.
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Old 06-25-2014, 07:59 PM   #34
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Some of those cheap chargers could be fire hazards. I would be very careful if they did not come with the original equipment.
I get them at resale shops... most branded for whatever device they were designed for... toys, blackberry's, intercoms and all kinds of phones... Just counted my "supply"... actually over 100 chargers/power supplies... am the go to guy in the neighborhood when someone needs an extra plug in or car lighter adapter or laptop and printer cords.

One of my hobbies buying old electronics of all kinds... just to see how they work... six big plastic tubs full. Never pay more than $2.... My toys. Vic20, Adam, TRS80, Apple IIe, Sinclair, Emachine(s) etc...
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Old 06-25-2014, 08:00 PM   #35
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Talk about inflation! Back when I was a kid, 3.6m/hr equaled 142 in/hr!
Gotta be more careful with decimal points.
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Old 06-25-2014, 08:03 PM   #36
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The electron motion down the wire is started by the electric field propagation in the dielectric material surrounding the wire. The speed of propagation depends on the dielectric constant of the material and is usually a large fraction of the speed of light in vacuum as you noted.
Right, but you said explain to a layman so I wasn't going to get into the fact that the electric field was actually propagating in the air between the wires (for a common lamp cord).

I see you are just trying to keep it real.
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Old 06-25-2014, 08:06 PM   #37
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I get them at resale shops... most branded for whatever device they were designed for... toys, blackberry's, intercoms and all kinds of phones... Just counted my "supply"... actually over 100 chargers/power supplies... am the go to guy in the neighborhood when someone needs an extra plug in or car lighter adapter or laptop and printer cords.

One of my hobbies buying old electronics of all kinds... just to see how they work... six big plastic tubs full. Never pay more than $2.... My toys. Vic20, Adam, TRS80, Apple IIe, Sinclair, Emachine(s) etc...
I cannot honestly say that some chargers are dangerous but have read a bit about unfortunate events.

Whenever I charge something I try to make sure the charger and electronics are in an area that has very few flammable materials around. Like the kitchen tile area for instance. Maybe I'm too cautious but it makes me feel better.
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Old 06-25-2014, 08:07 PM   #38
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Harder to explain to a layman is an electric field propagating in a vacuum. Actually that is hard to explain to a EE student.
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Old 06-25-2014, 08:11 PM   #39
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Re: electron flow... I had it explained to me, that the electrons don't actually move on a wire, but rather are absorbed by the atoms that constitute the transmission medium (in this case wire)... and thereafter being thrown off to the next atom, and so on down the line. That's an old, old memory gleaned from my college roomate, who had as his major thesis, the movement of electron (energy) in different gasses... shock tubes. 60 years ago...
I bow to newer technology...
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Old 06-25-2014, 08:14 PM   #40
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Many moons ago I had EE courses in Solid State Theory, Quantum Mechanics, E&M, etc. I never quite made the leap between the electron drift behavior in a wire and the EM field propagation. I'm aware of some of the loose qualitative explanations above so am not totally clueless.

Any of you have a good suggestion for a source that presents a qualitative explanation in a somewhat higher level discussion? If it had some equations I could perhaps handle that ... maybe.

I'm sure the OP did not expect us to get sidetracked in the land of physics. Sorry about that.
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