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

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Discussion Overview

The discussion revolves around the behavior of electric fields and currents within an ungrounded Faraday cage. Participants explore the implications of introducing current and charges into the cage, examining both theoretical and practical aspects of its shielding properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that introducing electrons onto a Faraday cage results in a uniform charge distribution, leading to no electric field inside the cage.
  • Others argue that if a charge is placed inside the cage, it creates a field between the charge and the cage's potential, which contradicts the idea of no electric field.
  • There is a claim that if there is no potential difference inside the cage, there can be no current flow.
  • Some participants inquire about the effects of external currents and whether they can penetrate the cage's internal face.
  • There are discussions about how charges redistribute themselves in response to external fields, potentially generating electric fields outside the cage when charges are present inside.
  • Several participants express confusion regarding the implications of inserting current and how it relates to the behavior of charges within the cage.
  • One participant questions the relationship between excess charges and electric fields, suggesting that introducing current implies the presence of an electric field.
  • There are references to the effects of lightning strikes on a Faraday cage and whether a person inside would be safe if they touched the metal during such an event.
  • Some participants discuss the concept of a "perfect" Faraday cage and its theoretical implications for safety during electrical events.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the effects of introducing current into an ungrounded Faraday cage. Multiple competing views remain regarding the behavior of electric fields and charges, as well as the implications for safety during electrical events.

Contextual Notes

Participants reference various concepts such as electrostatics, induction, and Gaussian law, indicating a need for a deeper understanding of these principles to clarify the discussion. There are also mentions of quantum effects and the limitations of constructing a perfect Faraday cage.

Who May Find This Useful

This discussion may be of interest to those studying electrostatics, electrical engineering, or safety protocols related to electrical fields and shielding methods.

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).
 

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