Faraday cage question

  • #1

Main Question or Discussion Point

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?
 

Answers and Replies

  • #2
mgb_phys
Science Advisor
Homework Helper
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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.
 
  • #3
Don Carnage
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:
 
  • #4
berkeman
Mentor
57,469
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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.
 
  • #5
I mean if I insert current from outside, will it pass through the internal face? What will happen?
 
  • #6
128
0
isn't post #4 already stated clearly, the answer is no current inside ;)
 
  • #7
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.
 
  • #8
128
0
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.
 
  • #9
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" [Broken] or?
 
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  • #10
128
0
Like this http://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/FaradayscherKaefig.svg/180px-FaradayscherKaefig.svg.png" [Broken] or?
the E field is generated outside because of charge inside the cage, provided it is not grounded! ;) ;)
hope you can get the picture
 
Last edited by a moderator:
  • #11
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
128
0
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, lets hear what other might say on this. no picture here unfortunately.
 
  • #13
if my understand from wiki is correct, lets hear what other might say on this. no picture here unfortunately.
The above picture, wasn't correct?
 
  • #14
128
0
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 wanna check out some electrostatic concept(induction) and Gaussian law in order to understand how the cage work. gtg.
 
  • #15
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 wanna 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
128
0
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 gonna insert current flow?
 
  • #17
you can insert charge, but how you gonna insert current flow?
Current flow, with lighting.
 
  • #18
90
0
no matter what u do, nothing would happen to you if you are IN THE FARADAY CAGE!!!
 
  • #19
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
90
0
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
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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  • #23
3,077
3
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?
 
  • #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?
 

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