# Electric fields of dipole

1. Sep 8, 2008

### the7piano

1. The problem statement, all variables and given/known data

A rod of length 2L lies on the x axis, centered at the origen, and carries a line charge

density given by t=T(x/L), where T is a constant. (a) Find an expression for the electric

field strength at points on the x axis, for x>L (b) Show that for x>>L, your result has the

1/x^3 dependence of a dipole field, and by comparison, determine the dipole moment of the

rod.

2. Relevant equations

dE = (k dq)/r^2

3. The attempt at a solution

dq=Tda, dE= (k dq)/(x-a)^2 = (kT/L) * (a da) / (x-a)^2

integral dE form -L to +L

E = (kT/L) * ( - x/(x+L) + x/(x-L) + ln( (x-L)/(x+L)) )

when x>>L , by using binomial expanding, the result what I have

1/x^2 dependence. Help !!!!!!!!

Last edited: Sep 8, 2008
2. Sep 8, 2008

### mezarashi

Could I get confirmation on this question? Normally when electric dipoles are talked of, we would look to find fields for distances perpendicular to the dipole rather than parallel.

3. Sep 8, 2008

### the7piano

The situation fof that problem, To find the fields for distances parallel to the dipole.

I think it doesn't matter whether perpendicular or parallel.

The result of both situation has 1/^3 dependence of a dipole field, I think