Electrostatic Force on b: Positive & Negative?

[Air]

1. All variables and given/known data:

$a = c = 1 \times 10^{-19} C$
$b = 2 \times 10^{-19} C$
Distance between a&b = b&c = 0.1m (b at origin, a at (0, 0.1) and c at (0, -0.1))


2. Homework Equations :

$F = k\frac{|q_1||q_2|}{r^2}$


3. The problem that I'm having:

Am I correct to think that the electrostatic force on b from other charges is at a minimum because the Force will be positive and negative (due to the nature of r ($\pm$ 0.1)) cancelling each other out?

 

[olgranpappy]

1. All variables and given/known data:

$a = c = 1 \times 10^{-19} C$
$b = 2 \times 10^{-19} C$
Distance between a&b = b&c = 0.1m (b at origin, a at (0, 0.1) and c at (0, -0.1))


2. Homework Equations :

$F = k\frac{|q_1||q_2|}{r^2}$


3. The problem that I'm having:

Am I correct to think that the electrostatic force on b from other charges is at a minimum because the Force will be positive and negative (due to the nature of r ($\pm$ 0.1)) cancelling each other out?

Yes, the force on b due to a is "pointing down", and the force on b due to c is "pointing up", and the magnitudes of those forces are equal (from your equation). And so the vector sum of all the forces on b is zero in the situation shown.

 

[Air]

Yes, the force on b due to a is "pointing down", and the force on b due to c is "pointing up", and the magnitudes of those forces are equal (from your equation). And so the vector sum of all the forces on b is zero in the situation shown.

I just realized that the radius will be squared hence the negative will also produce a positive force. How does it equal zero then (Surely, it will just equal 2F)? Am I to use another formula or is the electrostatic formula correct to use?