# Electric Field due to a Dipole (not on a z-axis)

1. Sep 6, 2009

### Oijl

1. The problem statement, all variables and given/known data
The figure shows an electric dipole. What is the magnitude of the dipole's electric field at point P, located at distance r >> d?

2. Relevant equations

3. The attempt at a solution

I suppose I could define the angle with which I could write Ey = Esin$$\theta$$, but this problem is a webassign.com problem, so it's online and I can't define anything.

The magnitude of the electric field at p due to the dipole would be very small, and I first estimated it to be zero (since the problem asks for an estimation anyway).

Without defining and using a theta, how could I represent the magnitude of the electric field?

2. Sep 7, 2009

### loveequation

Just introduce theta temporarily. It goes away in the end since you know what it is.

The electric field vectors of the two charges add in the $y$ direction and cancel in the $x$ direction. Hence
$$|\vec E| = |E_y| = (2 q/R) \sin(\theta)$$
where I will let you write down $R$ and $\sin(\theta)$ in terms of $r$ and $d$.

The rest you can do.

3. Sep 7, 2009

### rl.bhat

In the dipole one is +ve charge and the other -ve charge.
The electric field E = 1/4πεο*q/[r2 + (d/2)2]
Their y-components cancel out and x-components add.

4. Sep 7, 2009

### loveequation

I maintain that the y components add. Think of the magnetic field lines of the Earth at the equator.