# Homework Help: Electric Field at Point question

1. Oct 4, 2006

2. Oct 4, 2006

3. Oct 4, 2006

### FocusedWolf

Thx, my confidence doesn't feel so shattered now :P

4. Oct 4, 2006

### Staff: Mentor

Though your work was just fine, you could save yourself some effort by using a symmetry argument.

5. Oct 4, 2006

### FocusedWolf

Teacher just got back to me... turns the side of the square is A...somehow looking at how they depicted A in that drawing made me think A was the distance from center... even though it says in the instructions that A is the whole side... zzz

using distance from center = a/2 then problem comes out to their answer 3.05e13

6. Oct 4, 2006

### Staff: Mentor

D'oh! Sorry about that... I must have been sleeping also. (I just looked at the diagram and ASSumed that "a" was the distance from the origin.)

7. Oct 4, 2006

### FocusedWolf

It's ok...this problem was booby trapped!

8. Oct 5, 2006

### FocusedWolf

o quick question...

is the unit vector R always in direction from the charge to the point..QP

9. Oct 5, 2006

### Staff: Mentor

Yes, if you mean in the expression for the field at point P due to charge Q:
$$\vec{E} = \frac{k Q}{R^2} \hat{R}$$