Faraday's Cage

[5614]

Let's put it another way, in England during one thunderstorm in 1360 more knights were killed by lightning than were killed the battles of Crecy and Poitiers. The suits of armor did not protect them from the current, as they were touching the charged metal.

 

yes, but asuming that faradays cage doesnt let electrical fields inside.....

 

the holes in the knights armour will decomplete the circuit, therefore it can no longer be considered as faraday's cage......

plus, the suit of armour could be of a low conductivity, which reduces the effect of faraday's cage,

 

i think that the suit of armour will DEFINATELY stop the electrical field, but will it stop the electrical current / voltage from the lightening?????

 

[is the question now]

i thought it would, but now, it doesnt sound so realistic!?

[5614]

this website:- http://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/E3/

 

says:

 

"A more impressive demonstration of the Faraday cage effect is that of an aircraft being struck by lightning. This happens frequently, but does not harm the plane or passengers. The metal body of the aircraft protects the interior. For the same reason, and if it were not for the highly flammable nature of petrol, a car would be a very safe place to be in a thunderstorm. "

 

so its saying that planes are safe, but cars are not, because of the fuel in cars!!! but planes have fuel too!!! whats going on, why are plane passengers safe, and car not, both metal shells, both with fuel! whats going on?

 

if the passengers are safe from electrical current, and therefore also safe from electrical shocks, y isnt the fuel?

[Lance]

 

so its saying that planes are safe' date=' but cars are not, because of the fuel in cars!!! but planes have fuel too!!! whats going on, why are plane passengers safe, and car not, both metal shells, both with fuel! whats going on?

 

[/quote']

 

Have you ever tried to light kerosene with a match?

 

I think in reality the fuel is safe too. But then again nobody wants to get sued for saying cars are safe in any aspect.

[5614]

i know fuel is [crap, whats the word?] it can catch fire! and explodes! yes i know, [well not explodes, but yes i know what happens]

 

but say if you have a fuel tank, which is metal, if that was hit by lightening, would faraday's cage save the fuel from ignition, or would it all blow up!!!????

 

 

i think that a suit of metal armour will DEFINATELY stop the electrical field, but will it stop the electrical current / voltage from the lightening????? hitting you, and possibly, quite likely killing you!?!??!?!?

[pulkit]

God damn it ! if u r inside a conducting shell u can't get a shock !!

Don't you know anything about physics ??????!!!!

Current needs a potential difference which you can't have in a conductor because it is equipotential.

In short, YOU CANNOT GET AN ELECTRIC SHOCK inside a faraday cage !!

Completing a circuit is not enuf, you must have a driving potential.

[5614]

presumably the shell has to be a full outter shell, it cant have holes?

 

i want to belive u [pulkit], it just sounds dodgy, that a guy in a suit or aromour CANNOT be elctrocuted! soz

[YT2095]

chain suits are used by coilers all the time, some of the TV stunts you see are guys or galls in such suits. YES it`s perfectly safe!

factor in the "Skin effect" also, you`ll know that what Lance and I are saying is true.

 

as for lightening, that really all depends on the weather, no 2 bolts are the same!

[Cap'n Refsmmat]

What are coilers?

[swansont]

A faraday cage is a closed metal surface which does not allow any electric fields inside it. It is IMPOSSIBLE for you to get a shock sitting inside it.

 

 

I'm sorry' date=' but you are not correct. A faraday cage is not some technobabble about a quasi mystical shield, it could just be a metal bucket. In fact, it is a metal bucket.

[/quote']

 

A bucket (with lid) is a closed metal surface. What part of pulkit's post is technobabble or mystical?

 

If the shell is grounded and you aren't touching it (i.e. part of the shell), you should be fine. It can be a mesh, and will keep out EM radiation whose wavelength is large as compared to the mesh size. (note that "solid" metal looks like a mesh to high frequency radiation whose wavelength is smaller than the atom separation distance, so it won't be an x-ray or gamma shield)

[YT2095]

yup, X-rays (Gamma) are in fact used to X-Ray welding joints on certain types of equip, metal is NOT a blocker for these types of radiation unless they are suitably thick enough to absorb the incoming rad.

a Farraday cage is limited somewhat by the frequency used

[NavajoEverclear]

what if you insulated the suit?

[pulkit]

note that "solid" metal looks like a mesh to high frequency radiation whose wavelength is smaller than the atom separation distance, so it won't be an x-ray or gamma shield

metal is NOT a blocker for these types of radiation unless they are suitably thick enough to absorb the incoming rad

Small sub-question : When you want to block out gamma radiation you can make use of thick lead blocks. Is it just the thickness of the metal or some property of lead that is being utilized as well?

[Cap'n Refsmmat]

The density. It's heavy, and so has more atoms in it to block the radiation.

[YT2095]

Thickness only applies when refering to a specific material

 

for example, if a gamma ray were to try pass through a meter of aluminium, it might encounter 100 units of obstruction, if it were to be 2 meters then it would get 200 units of obstruction and so on.

if it were 1 meter of Lead it may well get 500 units of obstruction!, why? because lead is more dense atomicly.

 

you can see this for yourself when you get equal size peices of lead and another material, Which weighs the most?

[pulkit]

Ah ! Now I remember, X-Rays for one fizz out (talking about intansity here) in an exponential decay when they move through a metal. I do not remember the name of the eponential decay factor, but it is considered shielded once their intensity drops to 1/e times the original intensity, which takes a constant amount of thickness each time it happens.

[swansont]

Ah ! Now I remember, X-Rays for one fizz out (talking about intansity here) in an exponential decay when they move through a metal. I do not remember the name of the eponential decay factor, but it is considered shielded once their intensity drops to 1/e times the original intensity, which takes a constant amount of thickness each time it happens.

 

It's called the linear attenuation coefficient. (which is strange at first glance because it's a term in an exponential decay equation, as you note)

 

The shielding depends on the number density and Z (atomic number). More atoms means more targets, as mentioned before, and higher Z also means more targets, because that's the number of electrons. A photon will interact via the photoelectric effect, Compton scattering, or pair production. The first two are interactions with the electrons, and the last takes place near a nucleus.

[5614]

chain suits are used by coilers all the time' date=' some of the TV stunts you see are guys or galls in such suits. YES it`s perfectly safe!

factor in the "Skin effect" also, you`ll know that what Lance and I are saying is true.

 

[u']as for lightening, that really all depends on the weather, no 2 bolts are the same![/u]

 

what are coilers???? [brain block!!! i know i know, just cant remember!!!]

 

what does that reffer to or mean????? [bit unerdlined / bold]

 

and so if got hit by lightening in chain mail, or metal mesh, does that work as faraday's cage?? im guessing not, but may as well ask!

[[Tycho?]]

what are coilers???? [brain block!!! i know i know' date= just cant remember!!!]

 

what does that reffer to or mean????? [bit unerdlined / bold]

 

and so if got hit by lightening in chain mail, or metal mesh, does that work as faraday's cage?? im guessing not, but may as well ask!

 

 

An enclosed metal mesh is a faraday cage, yes. At least it can be.

[5614]

'']An enclosed metal mesh is a faraday cage, yes. At least it can be.

 

even though metal mesh has holes in it?

 

like chain mail..... there are hundreds of little holes, so does that not break the 'enclosed'-ness about it!?

[Cap'n Refsmmat]

It does not break the "enclosed-ness". As long as the wavelength is larger than the mesh's open spaces, then it can't get through.

[5614]

It does not break the "enclosed-ness". As long as the wavelength is larger than the mesh's open spaces, then it can't get through.

 

two things:

 

first of all presumably, the holes would be bigger than the wavelength, if you look at chain mail, the holes can be up to 5mm across, [approx]

 

secondly, WHAT WAVES????? we are talking about being hit by lightening, lightening is a discharge of static electricity from the clouds, it surely is a flow of electrons, which would not classify as a wave....... so what are you talking about?

[Cap'n Refsmmat]

EM radiation. The skin effect is for electricity, as far as I know.

[[Tycho?]]

EM radiation. The skin effect is for electricity, as far as I know.

 

 

Yes. A faraday cage will act as an attena and absorb EM radiation of a wavelength longer than the diameter of the holes. I dont know if a surface has to be continous for the skin effect... although it was mentioned earlier that people wear chain mail mesh for dealing with something zappy. So I would assume yes, but it would depend on the size of the holes I would think....

[Cap'n Refsmmat]

Well, if the path of least resistance was THROUGH the holes, I suppose it wouldn't work.

So small holes, preferably.

[[Tycho?]]

Heh, yes indeed. And use the best conductor you can get your hands on, of course.