Electric field of a point near a dipole

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Homework Help Overview

The discussion revolves around calculating the electric field at a point near a dipole formed by two equal and opposite charges. The original poster seeks to express the electric field in terms of given variables and is particularly interested in the behavior of the field when the observation point is far from the dipole.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster expresses uncertainty about how to begin the problem and questions the analogy of the dipole to a wire. Other participants discuss the trigonometric relationships involved, questioning the use of sine versus cosine in the context of the geometry of the dipole and the point of interest.

Discussion Status

Participants are actively engaging with the problem, with some providing clarifications and insights into the forces at play. There is a recognition of the need to understand the geometric relationships involved, but no consensus has been reached on the approach to solving the problem.

Contextual Notes

The original poster has indicated a lack of confidence in their understanding of dipoles and the relevant equations, which may be influencing their ability to engage with the problem effectively.

jack343
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Homework Statement


Two equal and opposite charges form a dipole, as shown in the figure. What is the magnitude of the electric field at point P, in terms of k,q,d, and x? If point P is VERY far away, show that the result is approximately E = kqd/x^3.

http://imageshack.us/photo/my-images/403/img20111215161448.jpg/

please help :(


Homework Equations



F = kq1q2/r^2
E= F/q

The Attempt at a Solution



I don't know how to start? Does the dipole basically act like a wire?
I did some research on dipoles and nothing was related.
 
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Maybe this will help.
 

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Spinnor said:
Maybe this will help.

Thanks, now I know where the forces are going. But why is sin(theta) = d/2L? shouldn't it be cos(theta) since L is the adjacent side?

Can't we use the Pythagorean theorem to get that r = sqrt(L^2 + (d/2)^2) ?
 
jack343 said:
Thanks, now I know where the forces are going. But why is sin(theta) = d/2L? shouldn't it be cos(theta) since L is the adjacent side?

Can't we use the Pythagorean theorem to get that r = sqrt(L^2 + (d/2)^2) ?

My mistake, should be sin(theta) = d/2r. As r gets large sin(theta) gets small as required, the forces tend to cancel to a greater extent.
 
THANK YOU SO MUCH! I FIGURED IT OUT :)

Unfortunately, I bombed my electrostatics test today... great way to start winter vacation. :(
 
You lost a battle but you can still win the "war".

Good luck!
 
I lost another battle... deffered from my top school :/

anyhow, thanks for the help, in return I will help someone else.
 

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