MadSci Network: Physics

Re: What method can be used to store only positif or negetif elelectric charges

Date: Wed Dec 8 13:43:32 2004
Posted By: Chris Seaman, Staff, Electrical Engineering, Materials Engineering, Alcoa Technical Center
Area of science: Physics
ID: 1100478937.Ph

You will probably find it very difficult to generate and store a 2 
Coulomb charge.  Just to understand the rough dimension of your problem, 
let's see what it would take if you were to build a parallel plate 
capacitor.  The fundamental equation is

C = (Q/V) = K*e_0*(A/l)

C - Capacitance in Farads, F
Q - Charge in Coulombs, C
V - Potential difference, in Volts V
K - Dielectic constant, no units, Air ~ 1.
e_0 - Constant from Coulombs Law - 8.85e-12 C^2/(N m^2)
A - area of the plates, m^2
l - separation between the plates, m

For Q = 2C, at V = 1V (low voltage assumption),

A = 2.2599e+011m * l

If the plates were 1mm apart, you would need 2.2599e+08 m^2 of surface 

You can use the equation above to assess your constraints:
1) If you want large separation distance, you need more plate area.
2) If you increase the voltage, you will reduce the plate area.
3) If you increase the dielectric constant, you will reduce the plate 

Finally, I'm not sure how you will get "unconnected" electric fields.  
Anytime you store a charge, there has to be an opposite charge created.  
You may find ways to distribute it, but it will exist, and will interact 
with any nearby object.  If you have ever charged a rubber ballon you can 
make it attract hair or other light objects.  The charge is interacting.  
An electroscope is a device to detect the existence of a nearby charge; 
the charge interacts with it in a visible manner.

If you perform a web search on "electrostatic generator", you will find 
lots of information and projects on generating and storing charge.  See 
Bill Beatty's page,, with projects 
and links to other information.  Maybe some of these will help.  At least 
you can have fun trying.

Chris Seaman
Alcoa Technical Center

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