Coloumbs law with inverse cubic

  • Thread starter yusufali
  • Start date
  • #1
2
0
1. Homework Statement
A permanent electric dipole consisting of charges +q and -q
separated by the fixed distance s. Charge +Q is distance r from
the center of the dipole. We'll assume s << r.

a) Use the binomial approximation (1+x)-n ~= 1-nx if
x << 1 to show that the net force exerted on the dipole by charge +Q
is Fnet = 2KqQs/r3


Homework Equations



F = Kqq/r2

3. Attempted Solution

F = +kQq/(r+s/2)2 - kQq/(r-s/2)2
F = -2kQq(rs)/( (r+s/2)2 * (r-s/2)2 )

i cannot figure out the rest from there...
 

Answers and Replies

  • #2
6,054
391
You have been instructed to use ## (1 + x)^{-n} \approx 1 - nx ##, when ## x << 1 ##. Why are you ignoring this?
 

Related Threads on Coloumbs law with inverse cubic

  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
3
Views
5K
  • Last Post
Replies
2
Views
743
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
12
Views
3K
  • Last Post
Replies
4
Views
3K
Replies
2
Views
3K
Replies
3
Views
2K
Top