# Homework Help: Electric field problem

1. Jan 21, 2006

### Punchlinegirl

Consider three charges arranged as shown.

6.5 $$\mu C$$ 4.5 $$\mu C$$ -1.2 $$\mu C$$
x--------3.9 cm----------x-----1.2 cm-------x

Sorry, I can't post the picture on here, but basically it's 3 charges in a row, seperated by 3.9 and 1.2 cm.

What is the electric field strength at a point 2.7 cm to the left of the middle charge Answer in units of N/C.

First I drew a diagram and figured out that the total E field would be to the right
The point would be located 1.2 cm to the right of the first charge, and 2.7 cm to the left of the second charge.
Then I used the equation for Electric Field, k*q/r^2
k*(6.5 x 10^-6)/ (.012)^2 - k*(4.5 x 10^-6)/(.027)^2 + k* (1.2x 10^-6)/ (.012)^2 .
where k= 9 x 10^9.
Plugging in and solving gave me 4.26 x 10^8 N/C, which isn't right... can someone please help me?

2. Jan 21, 2006

### Chi Meson

recheck that third distance.

3. Jan 21, 2006

### Punchlinegirl

I got it... thanks