• Support PF! Buy your school textbooks, materials and every day products Here!

Electric potential problem

  • Thread starter debwaldy
  • Start date
  • #1
38
0
1. Homework Statement
derive an expression for the electrical potential at a distance x measured along the axis from the centre of a circular ring of radius R on which a charge Q is uniformly distributed.hence derive an expression for the electric field strength at this point


2. Homework Equations
to be honest im not too sure where to go after:
V= -⌠E.dl
any guidance at all would be much appreciated!!!thanks:biggrin:


3. The Attempt at a Solution
 

Answers and Replies

  • #2
957
0
It looks like a start, what if the "ring" were simply two charges, each of 1/2Q, and -r,0 and r,0 relative to a test charge at 0,x. What would that look like?
 
  • #3
41
0
This simply involves a lil integration.

Q is distributed uniformly throughout the ring. This linear charge denstity on it would be lambda= Q/2pi*R.

Let dV due to each infinitesimally small element (dl) on the ring = (1/4pi*epsilon)*(lambda*dl/(x^2+R^2)^1/2.

Then just integrate from 0 to 2pi*R.
 
  • #4
38
0
oh i see, so its ok to treat them as 2 separate point charges and then sum the electric potentials at the end.
doing this i got an expression:
V= - Q/4*pi*ε(x^2 + R^2)^1/2

and E= dV/dx
E = - [Qx]/[4*pi*ε(x^2 + r^2)^3/2]
 
  • #5
957
0
no, what i meant was look at it first as 2 point charges, then 4, then an infinite number spread around the ring, but Mr 4 points the way I was hinting at in post above directly.
 
  • #6
41
0
Quite so. I think your logic would be more useful in some questions. Thanks for that denverdoc.
 
  • #7
957
0
Quite so. I think your logic would be more useful in some questions. Thanks for that denverdoc.
Still getting the hang of helping without doing the work, ie trying to help posters conceptualize w/o telling them how to pursue directly. Sometimes I think I just add to the confusion:grumpy:
J
 
  • #8
41
0
Nope. I get you loud and clear! Maybe its coz I'm just as confusing!
 

Related Threads for: Electric potential problem

  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
10
Views
4K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
4
Views
516
Top