Electric Field Zero Points: Square Arrangement of Charges | Homework Question

[bap902]

Homework Statement

Four charges are arranged on the corner of a square. At which points is the electric field equal to zero?

Diagram:
http://img126.imageshack.us/img126/1994/diagram2zb7.png

Homework Equations

None

The Attempt at a Solution

I chose A and B because the charges are equal so therefore the electric field will be zero right inbetween them.

 

[LowlyPion]

Certainly the x components of the fields are balanced at A & B, but what about the field in the y direction at A & B? Is it 0 at those points?

 

[bap902]

Thanks for your help. I don't know about the y direction.

 

[LowlyPion]

When you are at A what is the field from the far away negative charges? It would be non-zero wouldn't it?

Likewise at point B for the positive charges.