# Point charge formula and set-up

• rocomath
In summary, Coulomb's Law states that the force between two point charges is equal to the product of their charges divided by the square of the distance between them, multiplied by a constant. To solve for the position of a third charge in a set-up with three charges, the magnitude of the force between each pair of charges is calculated and the direction is determined based on the signs of the charges. This is done in a cartesian coordinate system, with the resulting net force on the third charge being the sum or difference of the individual forces.
rocomath
I just have a general question. Coulomb's Law is ...

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

Ok, solving this question ...

Three point charges are arranged along the x-axis. Charge $$q_1=+3.00\mu C$$ is at the origin, and charge $$q_2=-5.00\mu C$$ is at $$0.200 m$$. Charge $$q_3=-8.00\mu C$$. Where is $$q_3$$ located if the net force on $$q_1$$ is $$7.00 N$$ in the -x direction?

In the set-up, why is that in order to solve for the correct answer. I ignore the absolute value?

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The charge sign (+ or -) has a direction in respect to the unit vector r. What you're using is a cartesian coordinate system. To deal with this, get the magnitude of Fe between each charge and simply put a + or - in front depending on what the direction of the force is.

There is a force of attraction between q1, q2 and q1, q3. So the net force on q1 is the sum or difference of these forces depending on whether they are in the same side or in the opposite side of q1. You will get two answers.

## 1. What is the point charge formula?

The point charge formula, also known as Coulomb's law, is used to calculate the electrostatic force between two charged particles. It states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

## 2. How is the point charge formula set up?

The formula is set up as F = k * (q1 * q2) / r2, where F is the force, k is the Coulomb's constant (8.99 x 109 N*m2/C2), q1 and q2 are the charges of the two particles, and r is the distance between them.

## 3. Can the point charge formula be used for both positive and negative charges?

Yes, the formula can be used for both positive and negative charges. The positive or negative sign of the charges will determine the direction of the force, with opposite charges attracting each other and alike charges repelling each other.

## 4. Is the point charge formula valid for all distances?

No, the point charge formula is only valid for point charges, which are charged particles with no dimensions. It becomes less accurate as the distance between the charges increases, and it is no longer applicable when the distance is large compared to the size of the charges.

## 5. What are the units of measurement for the point charge formula?

The units of measurement for the point charge formula are Newtons (N) for force, Coulombs (C) for charge, and meters (m) for distance. It is important to use consistent units for all variables in the formula to get an accurate result.

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