Finding the net electric field

[xapril]

Homework Statement

Find the electric field at the center of a square having side = 1m and having the following charges at each corner:

Q1:-1 x 10^-6
Q3: -2 x 10^-6
Q2: 2 x 10^-6
Q4: -1 x 10^-6

(Q1 is upper left corner, Q2 is upper right, q3 is lower left and Q4 is lower right)

Homework Equations

E= k*q/r²

The Attempt at a Solution

I used the equation to found the electric field for each of the charges (Q1: -18000, Q2: 36000, Q3: 36000, Q4: -18000) . But now I don't know what to do

 

[ehild]

Those fields are vectors. What are their directions?

ehild

 

[thebigstar25]

you can use the following fact about the field produced by positve charge and negative charge:

http://img687.imageshack.us/img687/4395/20195796.jpg

then your problem is as the next figure :


http://img24.imageshack.us/img24/9859/62805015.jpg

then as ehild sayed, find the vector addition at the center .. I think now its clear how to go on from there ..