# Electric field of a dipole at an offset point

1. Jan 24, 2016

### cj

Note: Post edited by moderator:

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

2. Relevant equations
I can't use voltage, nor polar coordinates (got to stick with cartesian).
Cartesian vector form of Coulomb's Law

3. The attempt at a solution

Last edited by a moderator: Jan 25, 2016
2. Jan 24, 2016

### haruspex

[ Items related to the initial post's original format removed by moderator ] ....

However, your handwriting and images are fairly clear, and you have taken the trouble to number all of your equations, which helps enormously, so I will answer.

It asks for two specific cases, a point on the x axis and a point on the y axis. You do not need to work with P in general position.
In your equations (3) and (5), compare the signs on the $\hat j$ terms.

Last edited by a moderator: Jan 25, 2016
3. Jan 24, 2016

### cj

Thank you. I appreciate your feedback. It, does, though, not help at all. What I provided is many steps beyond the scope of your suggestion, and focuses on how to handle the binomial version of the denominator, and how to process it. Again, thanks anyway.

Last edited by a moderator: Jan 25, 2016
4. Jan 24, 2016

### haruspex

Then you have not paid proper attention to my final comment:
[... some text unrelated to the problem at hand deleted by moderator]

Last edited by a moderator: Jan 25, 2016
5. Jan 24, 2016

### cj

I did; I suspect you didn't read my post in its entirety - or you simply are stumped. I'd follow up with clarifying comments - but there's a ton in my post already.

6. Jan 24, 2016

### haruspex

Which post? Your original images or something since? I still don't see anywhere that you admit to having a sign wrong in equation 5.

7. Jan 24, 2016

### cj

That was a typo: but it's the x-hat term in Eq. 5 (I prematurely assigned a "-" sign to reflect the -x direction of E-; but didn't carry it through).

I disagree; the j-hat terms are indeed correct as written (this has been widely confirmed, and is a moot point).

8. Jan 24, 2016

### haruspex

Humour me: plug x=0 into equations 3 and 5, and consider y>>a. What do you notice?