Can we have electrostatic levitation using capacitor type plates?


by ProgScience
Tags: capacitor, electrostatic, levitation
ProgScience
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#1
Apr18-11, 12:50 PM
P: 12
Hi all,

I am in the process of developing a science project. That is when I came across different types of levitation including electrostatic levitation. Maglev trains are a good example of magnetic levitation. We know that like charges repel each other.

Its on the last sentence that I want to put forward my query. Suppose, we build a capacitor type arrangement and charge it using battery; at the same time build a much smaller but similar type capacitor arrangement and charge it with battery; is it possible that we can suspend (i.e. in air without any other support) the smaller capacitor arrangement on the bigger one where the like charged plates face each other?

I have attached a picture of my thought. It is based on the assumption that such an arrangement will build static charges on faces of the plates.

I would like to know whether this is theoretically possible?

Thanks
Attached Thumbnails
Parallel Plates.jpg  
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Naty1
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#2
Apr18-11, 02:21 PM
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I'm pretty sure that would be very unstable....very difficult to reach some equilibrium condition....that probably means you'd need a sensing and control arrangement to vary voltage and charge to maintain equilibrium...analogous to negative feedback control in an amplifier circuit....
nasu
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#3
Apr18-11, 04:13 PM
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The field outside the capacitor is very small (ideally zero). So there is not much point in using capacitors in this way.

sophiecentaur
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#4
Apr18-11, 04:56 PM
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Can we have electrostatic levitation using capacitor type plates?


Millikan's oildrop experiment for finding the charge on an electron used the field between two plates to 'levitate' tiny drops of oil. But that was many orders of magnitude shy of what you are after.
You could imagine a pair of plates, one above and one below a polarised rail which could produce a lifting force. The problem, I think, is that the field you would need for any appreciable force would involve extremely high voltages and arcing would occur. The equivalent problem doesn't exist for maglev because you can use high currents without the problems associated with high voltages.

I don't think stability would be an inherent problem as long as the geometry could be got right.
pallidin
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#5
Apr19-11, 05:18 PM
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From your diagram you have 2 positively charged plates repelling each other.
That's fine! No need for a capacitor.
ProgScience
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#6
Apr20-11, 09:22 AM
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Quote Quote by Naty1 View Post
I'm pretty sure that would be very unstable....very difficult to reach some equilibrium condition....that probably means you'd need a sensing and control arrangement to vary voltage and charge to maintain equilibrium...analogous to negative feedback control in an amplifier circuit....
There will not be unstability. If at all it works, there will repulsive force on one side of the smaller plate due to positive charges which will be balanced by its weight. It must on the same lines of Maglev train.
ProgScience
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#7
Apr20-11, 09:27 AM
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Quote Quote by nasu View Post
The field outside the capacitor is very small (ideally zero). So there is not much point in using capacitors in this way.
I have read in another thread in this forum that the positive charges on the surface of capacitor plate facing away from the dielectric tends to be zero as almost all charges migrate inwards, i.e towards the negative charge. However, if you see magnetic levitation, the force of repulsion between the like poles is what suspends a load. Similarly, what I am interested is to know whether there will be positive charges on these plates so that they will provide the required force for suspending a weight.
ProgScience
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#8
Apr20-11, 09:33 AM
P: 12
Quote Quote by sophiecentaur View Post
Millikan's oildrop experiment for finding the charge on an electron used the field between two plates to 'levitate' tiny drops of oil. But that was many orders of magnitude shy of what you are after.
You could imagine a pair of plates, one above and one below a polarised rail which could produce a lifting force. The problem, I think, is that the field you would need for any appreciable force would involve extremely high voltages and arcing would occur. The equivalent problem doesn't exist for maglev because you can use high currents without the problems associated with high voltages.

I don't think stability would be an inherent problem as long as the geometry could be got right.
sophiecentaur, I agree that a field can possibly raise an object. But there will be instability due to Earnshaw's theorem. I was looking at lifting weights using force of repulsion like in the case of magentic levitaiton (Maglev trains).
ProgScience
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#9
Apr20-11, 09:35 AM
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Quote Quote by pallidin View Post
From your diagram you have 2 positively charged plates repelling each other.
That's fine! No need for a capacitor.
By using the term capacitor, I was referring to the arragement of plates which resembles of capacitor. There is no actual capacitor in this case. Only battery and set of plates.
Evil Bunny
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#10
Apr20-11, 01:47 PM
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Quote Quote by ProgScience View Post
There is no actual capacitor in this case. Only battery and set of plates.
How would you get like charges on two different plates with a battery?

I was actually going to ask this very question in a new thread, but this one seems appropriate...
nasu
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#11
Apr20-11, 02:48 PM
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Quote Quote by ProgScience View Post
By using the term capacitor, I was referring to the arragement of plates which resembles of capacitor. There is no actual capacitor in this case. Only battery and set of plates.
In your diagram there are two capacitors. You may not call them this but that's what they are.
ProgScience
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#12
Apr22-11, 05:35 AM
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Quote Quote by Evil Bunny View Post
How would you get like charges on two different plates with a battery?

I was actually going to ask this very question in a new thread, but this one seems appropriate...
I was thinking, when positive of battery is connected to a plate, that plate becomes positive. And negative conencted to another plate makes the plate negative. These two plates must be separated by the dielectric. However, whether they will have surface charges is a question.
Evil Bunny
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#13
Apr22-11, 06:09 AM
P: 237
Two conducting plates seperated by a dielectric is a capacitor. It absolutely will hold a charge... and in theory if you seperate them, they will each be holding surface charges opposite in polarity.

In reality... how are you going to do this? These two plates would have to physically be very close together. Seperating them with their respective charges intact seems like tricky business to me... I was just wondering how this was physically going to be accomplished.


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