# Homework Help: Find mag. of net electric field at the center

1. Feb 4, 2012

### mdawg467

1. The problem statement, all variables and given/known data
A point charge is placed at each corner of a square with side length a . The charges all have the same magnitude . Two of the charges are positive and two are negative, as shown in the following figure.

my figure: (image each charge represents a corner of the square)
(+q1)(+q2)
(-q3)(-q4)

What is the magnitude of the net electric field at the center of the square due to the four charges in terms of q and a ?
Express your answer in terms of the variables q, a, and appropriate constants.

2. Relevant equations
E=F/q
F=Kq2/r2

3. The attempt at a solution

I uploaded my work as an attachment..I'm getting the wrong answer. The correct answer is E=(4kq√2)/a2, whereas I kept getting E=(kq√2)/2a2

any ideas? thanks

File size:
38.4 KB
Views:
4,143
2. Feb 4, 2012

### SammyS

Staff Emeritus
You need to keep only the y -component of the electric field due to each charge.