# Electric Dipole in the near field region CLOSE to the source

by mrjimbo
Tags: dipole, electric, field, region, source
 P: 2 Hey Born2bwire, Well I was given: $$\varphi$$ = [-p(0)$$\varpi$$/4$$\pi$$$$\epsilon$$(0)c] ( cos$$\theta$$/r ) sin[$$\varpi$$(t- r/c )] and A = [-$$\mu$$(0)p(0)$$\varpi$$/4$$\pi$$r] sin[ $$\varpi$$ (t - r/c )] z$$\widehat{}$$ From there I used the grad of Psi and curl of A and the unit vector z definition to get the E and B fields where: E = -(grad Psi) - dA/dt B = (curl of A) Note: Those omegas, pis, epsilons etc. aren't superscripts btw just multiply, it looks like they are superscripts in the preview.
 Sci Advisor PF Gold P: 1,776 You should use the Tex now that it is working again. If you were given the exact potential and vector potential then all you have to do is use them to find the fields and that is the near field. The only difference between the near and far field is that in the far field you assume $$kr\gg 1$$. In this case, I can see that the E field will have a 1/r^2 component from the gradient of the potential and then a 1/r component from the time derivative. So the far-field would keep the leading order term. You could assume the opposite, that $$kr\ll 1$$ for the near field and drop the appropriate terms but I can't recall that being done. It really would be a matter of preference, especially for such a simple equation as in this case.