# Calculate the magnitude and direction of the net electric force

1. Jan 13, 2012

### crybllrd

1. The problem statement, all variables and given/known data

Three point charges lie along a straight line as shown in the figure below, where q1 = 6.60 µC, q2 = 1.41 µC, and q3 = -1.9 µC. The separation distances are d1 = 3.00 cm and d2 = 2.00 cm. Calculate the magnitude and direction of the net electric force on each of the charges.

I need to state the magnitudes and directions of all 3 charges.

2. Relevant equations

$F_{e}=k_{e}\frac{|q_{1}||q_{2}|}{r^{2}}$

3. The attempt at a solution

I have to convert the values to be able to properly use the equations.
q1=6.60e-9 C
q2=1.41e-9 C
q3=-1.9e-9 C
d1=.03 m
d2=.02 m
k=8.9876e9

I think I will only need help with the first part, I then should be able to do the rest on my own.
between q1 and q2:
$F_{e}=(8.9876e9)\frac{|6.60e-9||1.41e-9|}{.03^{2}}=9.29e-5$to the left

between q1 and q3:
$F_{e}=(8.9876e9)\frac{|6.60e-9||-1.9e-9|}{.05^{2}}=4.51e-5$ to the right

I will now subtract the answers: (9.29e-5)-(4.51e-5)=4.78e-5
The force to the left is greater than the force to the right, so it will move to the left.

The to the left part is obviously right.

What did I do wrong here?

2. Jan 13, 2012

### Staff: Mentor

I haven't looked at the rest of your work, but these are not quite right. Realize that μ means 10-6, not 10-9.

3. Jan 13, 2012

### crybllrd

Thanks a lot, I did have the conversions wrong.
I re worked it out and came up with the correct answer of 47.8 to the left.
Thanks again.