Faraday's Cage

[Guest Mystery]

As for the whole of the discussion (which I only just found through googling this subject matter), I must say to you all... This has been a pretty good debate thus far. Not the best, but damn interesting to read. Someone needs to copy this exchange down for posterity (with some editing, of course.)

 

Anyway, here is my bit to add...

 

The skinned suit of metal to block out a lightning strike is (in my opinion) a possible, albeit not entirely pheasible goal... But I think it might work (in a science fiction kind of way). The key, would be preventing an aperture, and with time we may have materials that allow the passage of light, but not be an even vaguely appealing conductor that we can meld with the metals of such a theoretical suit to prevent aperture. But the issue I have with the suit comes more along the lines of pheasability of material and use, namely the earlier mentioned heat changing properties in your conductor.

 

If the metal in use, your conductor, can handle the full heat of acting as a short-term capacitor (yes, not entirely accurate a term, but in my haste to finish, it works for now) for the lightning before it passes across the skin and exits to a grounding point (say, where you are standing), without melting or breaking down its conducting properties, then it is easily possible to withstand the bolt. But you would almost have to assume a perfect conductor was in use for that situation. I'd presume the charge would have harmful effects on your immediate surroundings if you weren't grounded, and the conductor discharged completely. However, it may attempt to dissipate into you at that point, aperture or no, since there would be no other path to travel other than through the conductor's middle directly. I'd be kind of interested to see if you, and the suit, might just combust or cook in that situation.

 

Might make an interesting experiment to try to issolate a perfectly hollowed metal sphere with an apple wrapped in a couple inches of insulation at it's core, inside of an insulated coating, and find some method for charging it to see if the sphere would either melt/detonate due to instability, make a baked apple, or retain the charge until some poor fool had to take the outer coating of insulation off. Then again, assuming a perfect conductor, and perfect insulator... Then again, getting the energy into it under such conditions may more difficult than surviving a lightning bolt. That is of course, unless the sphere acted as a transformer for incoming EM radiation that could transfer it into a direct charge... In which case, I'd shake that man's/woman's hand.

 

After that bit of rambling... I would say it could work under circumstances in which there was a method to keep the occupant of such a suit a) alive without apertures, aka not enough air unless it was monstrously large, no possible way to remove waste, no way to intake sustenance, and thus no longer a skin and more of a... well, vehicle, and b) if there were a method of making such a suit that wouldn't kill the occupant during fitting, as it would have to be -perfectly- sealed to maintain an effective Faraday Cage, and to do that with no holes/apertures.

 

This may bring ones mind back to the arguement that in this case, a cage rather than a skin might work around the body. But since the energy passes along the surface of the cage (this includes the inside of the mesh, which is easily accessible depending on the gauge/thickness of the conductor), it would have to be well-lifted up from the occupant to prevent contact, by many layers of insulation. The reason a cage works, at least for electromagnetics is that they may disperse into the surface of the cage, but you don't intend to be hugging it at the time. You could hold a cage while it disrupted EM, but I wouldn't advise offering any path at all to a lightning bolt, by direct contact.

 

Then again, I'm more writer than electrician, so this is just more wood for the fire, more energy for thought than anything. I love a good bit of theoretical science.

[Lance]

One day a pear named Fred decided to go on a walk.

 

 

Fred was enjoying himself when the sky darkened.

 

 

Soon after that Fred was struck by lighting.

 

 

Thankfuly Fred survived but he wanted to make a suit that would protect him if he was ever struck again. He put a strip of aluminum tape from above his head to under his toes. He then Put the probes of a voltmeter deep into his head and toes.

 

 

He then took another walk and was soon struck by lightning.

 

 

This time he didnt feal a thing and the volt meter never read above 0.4V!

 

OK, obviously I was a bit bored, but hey, Fred and my expensive multimeter survived a 500KV simulated lightning struck OK with some very large holes in his ‘faraday’ suit.

[5614]

nice pics, how did you generate the 500KV?

 

this shows electricity taking the easiest route, not a faraday cage.

 

a similar effect is shown on tall buildings when you have a wire from the topmost point, the lightning flows down the wire instead of through the building.

 

outta interest, what kinda resistance does a pear give and also, what was the voltage before the Al strip was used?

[Lance]

this shows electricity taking the easiest route' date=' not a faraday cage.

[/quote']

 

Thats the point! It’s not about a faraday cage. YOU DONT NEED A FARADAY CAGE. It’s about the skin effect and not being the lowest resistance.

 

a similar effect is shown on tall buildings when you have a wire from the topmost point, the lightning flows down the wire instead of through the building.

 

I said that 50 posts ago!

 

Sheesh!

 

nice pics, how did you generate the 500KV? outta interest, what kinda resistance does a pear give and also, what was the voltage before the Al strip was used?

 

That would be my tesla coil... Unfortunately it’s impossible to measure voltages that high so 500KV is just a guess based on how much air it can travel through.

 

I didn’t measure the resistance of the pair because it wasn’t critical to keeping my multimeter safe.

[5614]

eeee, i think i made lance angry, soz man

 

so you are saying that if a person, is standing in a lightning storm and they hold up a metal rod, whilsts they will most likely attract a bolt to the rod, they themselves should remain safe as all of the current will flow straight throught the rod, assuming that the rod is well grounded?

[Lance]

eeee, i think i made lance angry, soz man

 

Don't be sorry, Arguing is more entaining than doing nothing all day.

 

so you are saying that if a person, is standing in a lightning storm and they hold up a metal rod, whilsts they will most likely attract a bolt to the rod, they themselves should remain safe as all of the current will flow straight throught the rod, assuming that the rod is well grounded?

 

Yes, thats exacly what I'm saying. If you huged a lightning rod and lightning struck it you would be ok.

 

I think in some houses, some devices(like security systems) use the cold water pipe as a ground. This does not mean its unsafe to take a cold shower.

 

I use the cold water pipe as the ground for my coil also.

[5614]

yeah, um, argument close, go back to being bored or sumin!

 

bascially yeah, your right that the current would go down the pole, if you kinda read post #105, i wasnt arguing or saying it was wrong, i was just asking if that was what you meant! i didnt want this argument coz your right! i was just asking!

[Lance]

yeah' date=' um, argument close, go back to being bored or sumin!

[/quote']

 

Fine... I see how it is. By the way, although theoretically you should be ago if you go around hugging lightning rods, I would NOT want to be hugging one when it gets struck. OR be swimming in an ocean during a lightning storm...

[5614]

oh yeah, i know what i was gonna say, just because electricity takes the easiest router [with least resistance], doesnt mean it only takes that route:

 

if you have a basic parallel circuit, 3 bulbs in the one branch and 2 in the other, from what you are saying, [assuming the bulbs are equal in all their electrical properties] the electricty will only flow through the 2nd branch, as it has less resistance, and we know that there will be a voltage in both branches, if electricity only took the path of least resistance, then parallel circuits wouldnt work.... as only one of the many paths would have a voltage through, so we can deduce from this that in parallel ciruits, the voltage, and therefore [in normally cases] a current will flow through all the branches.

 

with our lightning we have the lightning [battery], the pole [connected to the ground] and me [in parallel with the pole, also touching the ground].

what you were saying is that I would not have a current flowing through me, because the electricity can flow down the pole, but if the electricty only took the easier route, then parallel circuits wouldnt work....

 

i do know that electricity will take the easier route, and would go down the pole and not you.... but how can you explain and that, and also take into account parallel circuits working?

[pulkit]

There is a difference here. When you talk of lightning, you are not in parellel with the pole. The circuit connections so to say have not been made yet. In this case there is a choice whether to travel through circuit (not branch) A which would involve going down a pole or through circuit B which would involve going down a human. The fact of the matter is that a parellel circuit will only be achieved if you are touching both the ground as well as the pole. Now there is no choice of circuits to pass through, you become a single circuit with a net effective resistance.

 

As far as parellel circuits are concerned, electricity does not ¨choose¨ its path, but it divides accordingly. The closest you can get to ¨choosing¨ is when you short circuit an element.

[Lance]

When lightning strikes, the air heats up and that path lowers its resistance an incredible amount. The resistance of the remaining paths is massive compared to the one path. So of course lightning will travel all paths but because of the huge resistances involved that doesn’t mean it will be visible or even measurable.

 

Theoretically you would be correct, but in practice it doesn’t always work out.

 

Edit: Nobody else has anything to say about Fred? Sheesh....

I thought it was funny...

[5614]

so by touching the pole, you would still be elctrocuted....? which is what i thought, as you become part of it, in a sense like what pulkit said in post #110

The fact of the matter is that a parellel circuit will only be achieved if you are touching both the ground as well as the pole. Now there is no choice of circuits to pass through' date=' you become a single circuit with a net effective resistance.

[/quote']

well we were talking about hugging a pole, which means that you would be elctrocuted.

 

fred was good, nice experiment, but i think there is a confusion somewhere.... in real life, with lightning and a pole [remember you are touching it] you would still be electrocuted, so fred the pear shows what happens on buildings, but wouldnt work on a human.... remember on buildings the wire is insulated, on fred and hugging a pole, the pole wouldnt be insulated, you would become part of it and you would get a current through you.

[Lance]

Of course you would get a current through you! That’s what Fred showed you! The current wouldn’t be any wear near enough to electrocute you though. Fred showed this perfectly. Remember there was a current flowing through Fred with the aluminum but it was only 0.4V. The voltage that passed through Fred would be similar to what would pass through you. 0.4V!!!! Electricity does take all paths but not at the same power.

 

Also remember: Electrocute = Death

Shock= feeling of current flowing through you

 

 

Also take into consideration that when my coil is turned on neon lights with no contact will light up. This is a perfect example of electricity taking all paths but different power. The electricity is flowing through the air but the current is so low that it’s not visible.

[pulkit]

I think there is another factor to investigated here. The fact that a sharper object would have more chances of "catching" a lightning bolt - I say this because almost always those things on buildings are made sharp, thick and metallic. I don't fully understand why this happens. The only thing close it that I have studied is something called "corona discharge" whereby sharper objects tend to be able to discharge static electricity more easily than less sharp ones. Does this sharpness have anything to do with the situation in consideration ?

[5614]

Also remember: Electrocute = Death

Shock= feeling of current flowing through you

oh yeah' date=' soz, my mistake

 

Of course you would get a current through you! That’s what Fred showed you! The current wouldn’t be any wear near enough to electrocute you though. Fred showed this perfectly. Remember there was a current flowing through Fred with the aluminum but it was only 0.4V. The voltage that passed through Fred would be similar to what would pass through you. 0.4V!!!! Electricity does take all paths but not at the same power.

but surely as one 'body' [the pole and you together] there would be an equal current through you and the pole... i dunno, i've never thought of this before, actually, no there wouldnt, yeah, that para was right, i'll just leave this sentence to show my line of thought!

 

Also take into consideration that when my coil is turned on neon lights with no contact will light up. This is a perfect example of electricity taking all paths but different power. The electricity is flowing through the air but the current is so slow that it’s not visible.

um, i dont see the point in this para , current cannot be slow, just low, as in there are not as many electrons per cm^2 or cm^3, should it be, whatever! oh wait, i see, you are showing that the electricity is going through the neon lights as well as the air... oooooh

in that case: yeah i know, however i thought that there would be equal voltage at all points [you and in the pole] but now thinking about it, i spose there wouldnt have to be, i've never tried measuring voltage in different parts of a single wire.

[Lance]

Sorry! I meant low... not slow.

[5614]

I think there is another factor to investigated here. The fact that a sharper object would have more chances of "catching" a lightning bolt

sharpness? as in a pointed edge? why would that make a difference.... actually it would for static electricity as it would mean all the charge gathers up in one point, when theres enough a spark would happen, which wouldnt happen if there had have been a bigger area, because then the charge would have been more spread out and less concentrated... but that is an area problem not a sharpness problem, so im not sure.

[Lance]

Yes, that would make a difference. Sharper objects have a lower break-out voltage than round objects. That’s why the toroid of tesla coils are round. They build up a higher voltage before breaking out so the arcs are longer.

 

However, I'm not really sure how to apply this particular problem. That would make a golf club more susceptible than a tree.

[[Tycho?]]

I just have to say, that that pear experiment was amazing.

[Lance]

'']I just have to say, that that pear experiment was amazing.

 

Thanks!

[pulkit]

What happened to Fred afterwards ?

Was he left fit for consumption ?

[Lance]

I burned ears into him with my neon sign transformer then I abandoned him in my lab.

[5614]

do neon sign transformers come with all neon signs? coz if so they are quite small....

[Lance]

do neon sign transformers come with all neon signs? coz if so they are quite small....

 

Yes, but the small ones are only for small signs and are solid-state/ high frequency. They wont work for a tesla coil.

[5614]

i was just thining about fred the pear [whos probably quite brown by now, as fruits go after a while!]

 

are we in agreement to say that different amounts of current can flow at different points in the same 'body' to more the Al tube than fred the pear, and more down a metalic rod that a human is holding onto?

 

http://www.hvfx.co.uk/stunts.html

is relevant to us because if you look at the bottom right stunt, apparently there is a guy in that faraday cage who is having "lightning bolts" shot at him by that tesla coil and of course as we have learnt, he will be totaly safe, because of the faraday cage effect.