How to Determine the Electric Field at a Specific Point?

[aliaze1]

Homework Statement

What are the strength and direction of the electric field at the position indicated by the dot in the figure?

Homework Equations

E_dipole = ~ [1/(4πε₀)] * [2p/r³ ]
on the axis of an electric dipole

E_dipole = ~ [-1/(4πε₀)] * [p/r³ ]
in the plane perpendicular to an electric dipole

The Attempt at a Solution

Which equation should I use??

Thanks

 

[Avodyne]

Neither. Your equations only apply if the two charges in the dipole are much closer together than the distance r from the dipole.

 

[aliaze1]

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?

 

[aliaze1]

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

 

[nicksauce]

what formula would i use?

Why not just use coulomb's law, and superimpose the two electric fields?

 

[aliaze1]

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=0.0125^0.5 (square root)

and doing all calculations, and then adding the two charges (3600 and -720) gives me 2880, which is incorrect...

 

[aliaze1]

lol so yea...umm...any help?