Finding the Optimal Ratio for Two Concentric Spheres in a Capacitor

In summary, the problem is to find the ratio of sphere b's radius to sphere a's radius in order to produce the lowest electric field between the two spheres. The solution involves using the equations C=[4pi(epsilon nought)][(ab)/(b-a)] and V=(Q/[4pi(epsilon nought)])(b-a)/(ab) and solving for Q=CV. Conceptually, as the radius of the spheres increases, the electric field decreases, so the ratio of b to a should approach infinity or a should be much less than b. The final solution is shown in the scanned images provided by the professor.
  • #1
Xinthose
10
0

Homework Statement



It's desired to build a capacitor which has two concentric spheres separated by a dielectric of high permittivity, low loss, and high dielectric strength. Calculate the ratio of sphere b's radius to sphere a's radius which produces the lowest electric field between the spheres.

Not sure how to start this one. Thank you for any help.
 
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  • #3


I do know, from Wikipedia, that concerning concentric spheres, Cap = 4 (pi) ε / ( (1 /a) - (1/b) )
 
  • #4


So what I've done on this problem so far is
C=[4pi(epsilon nought)][(ab)/(b-a)]
and
V=(Q/[4pi(epsilon nought)])(b-a)/(ab)
and plug it in Q=CV
i just get Q=Q

Conceptually
from E=kq/r^2 as the radius goes up the E field goes down
so the ratio from B to a would approach infinity or
A should be much less then A?
 
  • #5


The electric field E = V/d where d is the distance between the plates.
 
  • #6


Alright, but you eventually get E = Q / (4 * pi * ε * a * b) ; so how would you get a ratio from that from b to a ?
 
  • #7


You failed me Physics Forums; here is the scanned answer from my professor's solution set given to us after the test; I hope that this will help someone else out there; Make of it what you will; his handwriting is kind of hard to read

http://i633.photobucket.com/albums/uu57/Xinthose/scan0002.jpg

http://i633.photobucket.com/albums/uu57/Xinthose/scan0003.jpg

or if you prefer to see it on the forum

page 1
scan0002.jpg

page 2
scan0003.jpg
 
Last edited by a moderator:

1. What is the purpose of finding the optimal ratio for two concentric spheres in a capacitor?

The purpose of finding the optimal ratio is to determine the ideal dimensions of a capacitor that will maximize its capacitance, or ability to store electrical charge. This ratio can also affect the overall performance and efficiency of the capacitor.

2. How is the optimal ratio calculated?

The optimal ratio is calculated by considering the geometry of the two concentric spheres and the dielectric material between them. It involves using mathematical equations and simulations to determine the dimensions that will result in the highest capacitance.

3. What factors affect the optimal ratio?

The optimal ratio is affected by the radius and separation distance of the spheres, as well as the dielectric constant of the material between them. The dielectric constant is a measure of how well the material can store electrical charge and thus affects the overall capacitance.

4. How does the optimal ratio impact the performance of a capacitor?

The optimal ratio can greatly impact the performance of a capacitor. If the ratio is too small, the capacitance will be low and the capacitor may not be able to store enough charge. On the other hand, if the ratio is too large, the capacitor may become unstable and not function properly.

5. Are there any practical applications for finding the optimal ratio for two concentric spheres in a capacitor?

Yes, finding the optimal ratio is important in the design and manufacturing of capacitors used in various electronic devices. By maximizing the capacitance, the capacitor can store more charge and improve the overall performance and efficiency of the device.

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