Why does an amp make a 60hz sound when I touch the input cable?

[printer2]

Found the pictures.

[Austin]

Great illustration. A reminder of why wire length and equal length of each bit path on the bus became important when computers started to get fast,

Thanks Enzo, I didn't know that. Electricity (electrons) travels much slower than light getting faster with more voltage but electromagnetic waves can propagate at the speed of light in a vacuum and just under the speed of light in air and slower in more dense matter like copper.. I read that on wiki just now, something I probably should have done before posting that. Thank you

Great pics!! I gotta ask, wouldn't aluminum sheeting be 5 times cheaper and work almost just as well though? What is this room for?

Here is a good one:
http://amasci.com/miscon/speed.html

So radio waves are a form of ac.. Let me get this right... The cell phone couples to the tower and the waves propagate through that connection once tuned into, but why don't we also power our cellphones from the actual signal that we are coupled to?

Like this: http://www.youtube.com/watch?v=gcui0K7JZXA

or at least like this: http://hacknmod.com/hack/field-of-fluorescent-tubes-powered-by-ambient-current/

That last one goes perfectly with the theme of this thread.

[Tom Phillips]

...Electricity (electrons) travels much slower than light getting faster with more voltage ...I read that on wiki...

Much slower Faster with more voltage
There's the joke that says "it must be true because I read it on the internet" but it would be interesting to find all the facts & conditions and hear the absolute numbers associated with that wiki posting.

[Austin]

Much slower Faster with more voltage
There's the joke that says "it must be true because I read it on the internet" but it would be interesting to find all the facts & conditions and hear the absolute numbers associated with that wiki posting.

Faster with more voltage, the point of the particle accelerator! Speed of electrons varies with current density and resistance being equal more voltage equals more current. According to http://amasci.com/miscon/speed.html
the speed of electricity through a wire powering a 100 watt lightbulb with 100 hundred volts of DC current at 1 amp, is only three inches per hour. Wow.

[Enzo]

Three inches per hour? Well, no. Set up your DC supply - a battery and a light bulb and a switch. Use 12 inches of wire. DO you really think it will take four hours for the bulb to come on? If we are getting into all that stuff then you better define your terms. In this instance what do you mean by "electricity"? Someone may make a case that an individual electron in a wire - and even that is not well defined - may not stray far from where it started, electric CURRENT runs FAR faster than that. And as far as I am concerned, current is what electricity means. What happens in a wire and what happens inside a vacuum tube are not the same physical processes.


You can say things like "much slower" but put that in context. If light can circle the world 7.5 times a second in a vacuum and maybe in a wire it would only make it 7.2 times, well one might want to say that is MUCh slower, but one also has to admit that in front of you, that nanosecond wire only lost a fraction of an inch under those terms.

For any purpose you and I might have, speed of light is perfectly close enough. However "slow" electrons might be inside a tube or something, the signal through time in an amplifier is shorter than you or I will care about.


Imagine your cell phone was a flashlight. You turn it on and light spreads in all directions. On a cell tower are receivers - imagine they are guys with binoculars watching for flashlights. Now for communication, your phone also has little guys with binoculars and the cell tower has its own flashlights - it works both directions. The cell tower detects the emanations from your cell phone - it sees your flashlight. There is no "connection" made. In fact, the way cell phones work is that several towers detect your phone transmission, and they work together. WHichever one detects you the strongest is the one that does the communicating. And if you are driving down the road, your "connection" is handed off tower to tower. Waves don;t propagate through a connection, they just propagate in all directions. The cell tower detects it. Why can;t we power our cell phones off the air? Because the radio signals involved are microscopic. Amateur radio operators can talk to the other side of the world on 5 watts of power. Imagine a 5 watt light bulb on a tall tower, now imagine looking at it from 1000 miles away and being able to see it. You'd need some powerful binoculars. Well, a radio receiver can do that, but it has to amplify that tiny signal a LOT. You can make a simple crystal radio, and it indeed powers itself with the enrgy that comes down its antenna. But that energy is not enough to power the computer circuits, the lit touch screen, and all the rest of the crap in a cell phone.


Ah, how about the old Native American smoke signals we used to see in cowboy movies. The sender sent up puffs of smoke. Other people in all directions can see the signal, so a communication connection is made, but there is no connection between the fires. I can't keep my wigwam from the fire on that mesa on the horizon.

[Steve Conner]

Push an electron into one end of a wire, and one pops out of the other end almost instantly. The delay is as would be expected from the speed of light. The catch is that it's not the same electron. If you wanted the very same one that you put in, you might have to wait hours. The drift velocity is much slower than the propagation velocity. An academic question, since electrons are all identical and interchangeable according to quantum mechanics.

I would also like to point out that the guy who runs amasci.com was banned from 4hv.org for being fuller of s**t than Elvis's large intestine. He makes Soundguruman look like an oracle of wisdom.

[Austin]

Push an electron into one end of a wire, and one pops out of the other end almost instantly. The delay is as would be expected from the speed of light. The catch is that it's not the same electron. If you wanted the very same one that you put in, you might have to wait hours. The drift velocity is much slower than the propagation velocity. An academic question, since electrons are all identical and interchangeable according to quantum mechanics.

I would also like to point out that the guy who runs amasci.com was banned from 4hv.org for being fuller of s**t than Elvis's large intestine. He makes Soundguruman look like an oracle of wisdom.

Great explanation.

I think that was a cool link about the high voltage power lines 60hz electromagnetic field coupling with all the flourescent lightbulbs and lighting them up. We were wondering if the electric company had the right to sue for stealing energy... Same thing if you built a radio just for making electricity right near an AM radio station where you would get a hot signal 24 hours a day. It would take away energy from the tower by coupling with it and drawing from it, just like the flourescent tubes would take energy away from the wires that would otherwise have stayed in the wires and gone on to paying customers..

[Jazz P Bass]

electromagnetic field

Faraday found that this is what travels 'down' the wire.
At the speed of light.
William Thompson (aka: Lord Kelvin) proved this out when installing the first (and second (it broke in very deep water) and third) transatlantic cable.
It is a fascinating story in itself (laying the cable)

[Enzo]

Those light bulbs didn't pull power out of the power line, they were glowing from the field ALREADY flowing about them.

The flourescent tubes don't suck away power any more than an extra pair of ears sucks power from your amplifier.

[Steve Conner]

The first law of thermodynamics is conservation of energy. In layman's terms, the energy books must balance: any time some work is done (mechanical motion, heat, light etc.) some source of energy has to "pay" for it.

So yes, the fluorescent tubes do steal energy from the power lines, and yes, your eardrums suck up power from the loudspeaker. In those cases, the amount of power is so piffling that it is easy to ignore, although I once read of someone who was sued by the power company for stealing power by capacitive coupling, essentially no different to the fluorescent lamps. The power company won.

[J M Fahey]

Yes, the energy to light the tubes came from the power lines.
No, he was not "stealing" (not in the Legal meaning anyway), the power line was *already* radiating all that electromagnetic field, fluo tubes or not.
If they're uneasy about it, let them distribute power using shielded wire.
I'm sure any farm barbed wire (for example) running parallel to the line at the same distance, will absorb more radiated power than a fluo tube, simply because it's a longer "antenna" and lower resistance.
Hey!!, even wet earth along the path must cause *some* eddy current loss !!!

[Austin]

I don't believe that eardrums hearing a speaker and the tubes coupling to the power line are even remotely the same thing because our ears do not couple to the speaker in any way other than hearing it, a one way thing. The tubes glowing under the electromagnetic field interact with it and sort of pull on it and change its shape, your ear does not interact with the speaker at all becaue the same energy flows no matter if there are ears to hear it or not. Not so with the tubes as they they really do couple to it and draw energy from it once connected that would have stayed in the magnetic field, the field was already there but may have stayed contained, unless as JM put it, coupled to a wire fence somehow. A transformers primary with nothing connected to the secondary is just an inductor or choke, near infinite impedance to AC but if you short the secondaries wires or connect a load then you draw energy from the magnetic field, energy that was already there but not coupled to anything so it stayed there. If enough tubes were placed under the wires or all around them the power used would continue to add to the load of the power station where it came from because not only would it have to power the town the wires were going to but now it would have run all those extra lights... And the power company wouldn't like that I bet. Anyways there was my argument, are we having fun yet? I know I am, thanks for indulging me, I love this stuff.

[Steve Conner]

Anyone who has ever run sound at a gig knows that the levels have to be turned up once the crowd arrives, because bodies and clothing absorb sound better than walls and floors. I'd bet that ears absorb sound better still.

Power lines hardly radiate any energy. The field around them is reactive: from a circuits point of view, the electric field looks like a capacitance to ground and the magnetic field looks like a series inductance. Neither field represents a loss of energy, both can be (and are) cancelled out by the power company using equal and opposite reactances.

Sticking fluorescent tubes in the ground underneath them just makes the capacitance to ground more "lossy".

[J M Fahey]

And we *are* having fun here.
Just wait untill the redheads in small bikinis arrive, in a couple minutes.

[Enzo]

The eardrum thing, OK, the point is that to move your eardrums, it requires some force, no matter how tiny. SO like carpet on the wall, your little eardrum absorbs some energy that could be going on to the next ear. However the effect is so small you couldn;t measure it with our equipment. The ear thing does not affect the amount of energy the speaker emits, but in some tiny way it affects how much of it goes where.

Experiment. Go to a live outdoor concert. Listen to the speakers while standing out in the open, now stay the same distance from the speakers, but stand in front of a cement wall. The power from the speakers didn't change, but the sound you hear sure did.


Same thing with the flour tubes. The flourescent coating on the tube will glow in the presence of the electrical field. They may act as a conduit for some charge in their immediate vicinity, but I have to think any loading on the power grid would be also about unmeasurable. Way too many db down, so to speak. I think of it like rain on your roof. It lands in drops, all spread out. If you have a gutter along the eave, it gathers all the rain and concentrates it in one spot - it acts as a conduit - forming a nice visible stream. But it doesn't diminish the rain that falls on the next house over. Or indeed on your roof.