# Calculating the electric field

by aliaze1
Tags: electric, field
 P: 177 1. The problem statement, all variables and given/known data What are the strength and direction of the electric field at the position indicated by the dot in the figure? 2. Relevant equations Edipole = ~ [1/(4πε0)] * [2p/r3 ] on the axis of an electric dipole Edipole = ~ [-1/(4πε0)] * [p/r3 ] in the plane perpendicular to an electric dipole 3. The attempt at a solution Which equation should I use?? Thanks
 Sci Advisor P: 1,128 Neither. Your equations only apply if the two charges in the dipole are much closer together than the distance r from the dipole.
P: 177
 Quote by Avodyne Neither. Your equations only apply if the two charges in the dipole are much closer together than the distance r from the dipole.
what formula would i use?

P: 177

## Calculating the electric field

my textbook uses these forumulas...so i tried the problem using them

so here is my process:

p = qs

s=0.1
q=1*10-9
p=1*10-10

1/(4πε0) = 9*109

r=0.05m

plugging everything into the second equation {[-1/(4πε0)] * [p/r3 ]}, i get -7200, but this is incorrect
HW Helper
P: 1,276
 Quote by aliaze1 what formula would i use?
Why not just use coulomb's law, and superimpose the two electric fields?
P: 177
 Quote by nicksauce Why not just use coulomb's law, and superimpose the two electric fields?
good idea..this was my original approach, which didn't work for some reason

E=[1/(4??0)]*[q/r2]

using the two charges:

q1=1*109
q2=-1*109

and their respective distances:

r1=0.05
r2=0.01250.5 (square root)

and doing all calculations, and then adding the two charges (3600 and -720) gives me 2880, which is incorrect...
 P: 177 lol so yea....umm...any help?

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