What Happens When Current is Introduced into an Ungrounded Faraday Cage?

AI Thread Summary
Introducing current into an ungrounded Faraday cage does not create an electric field inside, as the charges redistribute to maintain equilibrium. If a charge is placed inside, the inner surface of the cage becomes charged, but this does not lead to a potential difference that would allow current to flow. In the event of a lightning strike, the cage protects those inside by redirecting the electric field around it, although a perfect cage is theoretically required for complete safety. Real-world cages may not be perfect, allowing for potential risks during extreme conditions. Thus, while a Faraday cage generally provides protection, it is not infallible against direct lightning strikes.
Physicsissuef
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Hi! I want to know what will happen if I insert current (moving electrons) into Faraday cage, which is ungrounded? Will still there be no electric field, inside the cage?
 
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If you mean put electrons onto a faraday cage then it will have a uniform charge distributed over the surface and so no difference in potential and so no electric field.
If you mean put an electron inside a faraday cage then there is a field between the charged electron and whatever potential the cage is at.
 
Nope - there will be no potential difference inside the cage meaning no electron movement meaning no current.

So if you get hit by a lightning flying in an airplane nothing should happen - actually planes
are often hit by lightnings.. the lightning just warps around the plane and continues down into the ground.. pretty cool.. :rolleyes:
 
The purpose of a Faraday cage is to isolate the stuff inside from the stuff outside. If you introduce currents inside the cage, the cage has no shielding effect.
 
I mean if I insert current from outside, will it pass through the internal face? What will happen?
 
isn't post #4 already stated clearly, the answer is no current inside ;)
 
JayKo said:
isn't post #4 already stated clearly, the answer is no current inside ;)
Can you explain what is happening, please? I sow this quote from wikipedia but can't understand:
wikipedia said:
If a charge is placed inside an ungrounded Faraday cage the internal face of the cage will be charged (in the same manner described for an external charge) to prevent the existence of a field inside the body of the cage. However, this charging of the inner face would re-distribute the charges in the body of the cage. This charges the outer face of the cage with a charge equal in sign and magnitude to the one placed inside the cage. since the internal charge and the inner face cancel each other out, the spread of charges on the outer face is not affected by the position of the internal charge inside the cage. So for all intents and purposes the cage will generate the same electric field it would generate if it was simply charged by the charge placed inside.
 
Physicsissuef said:
Can you explain what is happening, please? I sow this quote from wikipedia but can't understand:

An external static electrical field will cause the electrical charges within the conducting material to redistribute themselves so as to cancel the field's effects in the cage's interior.

Well, if my understanding did not fail me, what quoted from Wiki simply means, Instead of generating the E field outside of the cage, this time round, the E field is generated inside the cage when you put a charge inside the cage.
 
JayKo said:
An external static electrical field will cause the electrical charges within the conducting material to redistribute themselves so as to cancel the field's effects in the cage's interior.

Well, if my understanding did not fail me, what quoted from Wiki simply means, Instead of generating the E field outside of the cage, this time round, the E field is generated inside the cage when you put a charge inside the cage.
Like this http://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/FaradayscherKaefig.svg/180px-FaradayscherKaefig.svg.png" or?
 
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  • #10
Physicsissuef said:
Like this http://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/FaradayscherKaefig.svg/180px-FaradayscherKaefig.svg.png" or?

the E field is generated outside because of charge inside the cage, provided it is not grounded! ;) ;)
hope you can get the picture
 
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  • #11
JayKo said:
the E field is generated outside because of charge inside the cage, provided it is not grounded! ;) ;)
hope you can get the picture
How is that possible? The E field is generated outside because of charge inside the cage? Do you have some picture?
 
  • #12
Physicsissuef said:
How is that possible? The E field is generated outside because of charge inside the cage? Do you have some picture?


if my understand from wiki is correct, let's hear what other might say on this. no picture here unfortunately.
 
  • #13
JayKo said:
if my understand from wiki is correct, let's hear what other might say on this. no picture here unfortunately.
The above picture, wasn't correct?
 
  • #14
Physicsissuef said:
The above picture, wasn't correct?

the above doesn't show any external E field. only when E field is present, the charges will redistribute itself, such that the effect is no E field inside the cage.

you may want to check out some electrostatic concept(induction) and Gaussian law in order to understand how the cage work. gtg.
 
  • #15
JayKo said:
the above doesn't show any external E field. only when E field is present, the charges will redistribute itself, such that the effect is no E field inside the cage.

you may want to check out some electrostatic concept(induction) and Gaussian law in order to understand how the cage work. gtg.
But man, we are talking about an excess of charges inside the cage. With inserting current, I also insert excess of charges, therefore, there must be somewhere excess of electric field.
 
  • #16
Physicsissuef said:
But man, we are talking about an excess of charges inside the cage. With inserting current, I also insert excess of charges, therefore, there must be somewhere excess of electric field.

you can insert charge, but how you going to insert current flow?
 
  • #17
JayKo said:
you can insert charge, but how you going to insert current flow?

Current flow, with lighting.
 
  • #18
no matter what u do, nothing would happen to you if you are IN THE FARADAY CAGE!
 
  • #19
esalihm said:
no matter what u do, nothing would happen to you if you are IN THE FARADAY CAGE!

That's the point. What is happening, so there nothing will happen you in the Faraday cage, if there is excess of charge?
 
  • #20
ALL the charge (the electrons) repel each other and try to move as far from each other as they can. They can move up to the sides, corners and outer faces of the cage, until then, they stay there.
that's why no matter what u do, nothing would happen to you if you are IN THE FARADAY CAGE

ok?
 
  • #21
esalihm said:
ALL the charge (the electrons) repel each other and try to move as far from each other as they can. They can move up to the sides, corners and outer faces of the cage, until then, they stay there.
that's why no matter what u do, nothing would happen to you if you are IN THE FARADAY CAGE

ok?

The current (the moving electrons) cannot pass to the internal face? As far as I know they travel from orbital to orbital, pushing themselfs?
 
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  • #22
Anybody knows?
 
  • #23
Given free charges not in equilibrium, like those introduced to the inside of a Faraday cage, how long do they resonate (as they redistribute on the conductor) until quantum effects are predominant?
 
  • #24
Physicsissuef said:
Current flow, with lighting.


this is getting out of hand! ;)
 
  • #25
Can I ask you some other question? What will happen, if I stand inside of ungrounded Faraday cage, and touch the metal from inside (which is not isolated with plastic or something), and in same moment lighting strikes, directly in the cage. Will I die?
 
  • #26
Physicsissuef said:
Hi! I want to know what will happen if I insert current (moving electrons) into Faraday cage, which is ungrounded? Will still there be no electric field, inside the cage?

Does the dome light work inside your car?
 
  • #27
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  • #28
Physicsissuef said:
Look at http://www.youtube.com/watch?v=mUWxYesR5Wo" Will the person inside the Faraday cage will die, if he touch it? Will the same happen with lighting strike?
To the degree that the cage is perfect no.
Given that it is not possible to construct a perfect cage, then for a direct lightning strike you could die.
 
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  • #29
NoTime said:
To the degree that the cage is perfect no.
Given that it is not possible to construct a perfect cage, then for a direct lightning strike you could die.
What is perfect cage, can you describe it with few words?
 
  • #30
Cage=Faraday cage.
Perfect as opposed to imperfect (or what we can actually build).
 
  • #31
Current will indeed flow through the wall of a Faraday cage; they have lights in there.

A car is not a particularly good Faraday cage. It is made of a poor conductor and has large openings together with lots of "sneak" paths.

There are at least two documented cases of a person(the same person!) being struck by lightning while inside a car (well, actually a truck in one case).
 
  • #32
(From an earlier post of mine.) Member NoTime has mentioned the same thing.

In the ideal case, the Faraday cage should be an unbroken hollow conducting shell. Then there cannot be any electrical field inside due to outside fields. In practice, it is made of fine mesh, and connected to the ground, that is earthed.

A heavy duty properly grounded cage will prevent lightning from passing through. But, theoretically, it's possible to imagine an exceptionally powerful bolt of lightning entering it, because it's a mesh, not an unbroken hollow shell.
 

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