Spherical capacitor RC system -- determine steady state charges

Click For Summary
SUMMARY

The discussion focuses on solving a problem involving a spherical capacitor RC system, specifically determining steady-state charges. The capacitance of a spherical capacitor is defined as C = 4πε₀R, where R is the radius and ε₀ is the permittivity of free space. Participants emphasize the need to find potential differences between the spheres and infinity, as well as between the spheres themselves (VAB and VBC). Attempts to simplify the problem by substituting spherical capacitors with parallel plate capacitors have proven incorrect, indicating the necessity of a more nuanced approach.

PREREQUISITES
  • Understanding of spherical capacitor capacitance (C = 4πε₀R)
  • Knowledge of potential difference calculations in electrostatics
  • Familiarity with the concept of equipotential surfaces
  • Basic principles of RC circuits and charge relationships (Q = CV)
NEXT STEPS
  • Research the derivation of capacitance for concentric spherical shells
  • Study the method for calculating potential differences in electrostatic systems
  • Explore the concept of equipotential conductors in electrostatics
  • Investigate advanced techniques for solving RC circuit problems involving capacitors
USEFUL FOR

Students and professionals in electrical engineering, physicists studying electrostatics, and anyone involved in analyzing capacitor circuits and their steady-state behaviors.

palaphys
Messages
266
Reaction score
17
Homework Statement
Three uncharged metallic balls of radii a, b and a respectively are connected to terminals A, B and C with the help of long thin conductors as shown in the circuit. Find charges established on each of the balls, when a steady state is reached after the switch is closed. Consider the balls to be at great distances from each other as well from the circuit and neglect internal resistance of the battery.
Relevant Equations
Q=CV ,V=iR
1757832369543.webp

This is the diagram given for the problem.
Now I was able to identify, that the fact that the capacitance of a spherical capacitor, with one plate and the other at an infinite distance, is somehow to be used in this problem, i.e ##C= 4\pi\epsilon_0R ##

IF I can replace all the spherical capacitors with parallel plate capacitors with the same capacitance, I can solve the problem very easily. Though this seems intuitive, it yields the incorrect result.
Looking forward on how to approach this problem.
 
Physics news on Phys.org
palaphys said:
Though this seems intuitive, it yields the incorrect result.
Please post your result and the official result if known.
 
Three spheres.webp
Here is your approach. Look at the figure on the right. Each colored region of space encloses equipotential conductors in the steady state.

Start by finding expressions for the potential difference between each sphere and infinity. Then find expressions for the potential differences ##V_{AB}## and ##V_{BC}.##
 
Last edited:
kuruman said:
View attachment 365510Here is your approach. Look at the figure on the right. Each colored region of space encloses equipotential conductors in the steady state.

Start by finding expressions for the potential difference between each sphere and infinity. Then find expressions for the potential differences ##V_{AB}## and ##V_{BC}.##
let me try this
 
kuruman said:
View attachment 365510Here is your approach. Look at the figure on the right. Each colored region of space encloses equipotential conductors in the steady state.

Start by finding expressions for the potential difference between each sphere and infinity. Then find expressions for the potential differences ##V_{AB}## and ##V_{BC}.##
sorry, long time but I feel I've tried enough. not getting how to proceed. trying to use V=Q/C
 
palaphys said:
sorry, long time but I feel I've tried enough. not getting how to proceed. trying to use V=Q/C
Q is what you are looking for.
What is C for a concentric shell capacitor in which the outer shell has infinite radius?
 
palaphys said:
sorry, long time but I feel I've tried enough. not getting how to proceed. trying to use V=Q/C
I repeat:
haruspex said:
Please post your result and the official result if known.
And your working, of course.
 

Similar threads

  • · Replies 26 ·
Replies
26
Views
3K
Replies
6
Views
1K
  • · Replies 1 ·
Replies
1
Views
3K
Replies
1
Views
8K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
6K