# Homework Help: What is the the electric field at a point midway between

1. Jan 21, 2010

### shimizua

1. The problem statement, all variables and given/known data
What is the the electric field at a point midway between a -7.39 uC and a +5.17 uC charge 3.32 cm apart? Take the direction towards the positive charge to be positive.

2. Relevant equations
E1=kq1/r^2
E2=kq2//r^2
E1+E2=Etotal

3. The attempt at a solution
E1=8.9E9(5.17E-6)/.0332^2
E2=8.9E9(-7.39E-6)/.0332^2
I got 4.1E7 and 5.97E7 which i added up for 1.014E8 N/C

2. Jan 21, 2010

### fluidistic

Are you sure you didn't make a sign error for E2?
Also, the charges are 3.32 cm apart. You are situated midway through them. How could then r be 3.32 cm?

3. Jan 21, 2010

### shimizua

wow thanks, i didnt even think about how it was in the middle. thanks again so much

4. Jan 21, 2010

### NewtonMDC

I'm working on this problem also, and getting something wrong. I'm using the same equation as you. Did you find that dividing r/2 gave you the correct answer?

5. Jan 21, 2010

### shimizua

um....ya. so i just divided the r by 2. but u still have to make sure you are squaring it? post up ur numbers and stuff and what you get if you are still having trouble and ill see if i can help you out

6. Jan 21, 2010

### NewtonMDC

What is the the electric field at a point midway between a -7.79 uC and a +5.66 uC charge 3.74 cm apart? Take the direction towards the positive charge to be positive.

So I did:

(9E9)(-7.79E-6)/(.00187^2)

and

(9E9)(5.66E-6)/(.00187^2)