# Two Point Charges: Physics Problem Help

• phunphysics2
In summary, the conversation is about solving a physics problem involving Coulomb's law and the E=k[q]/rsquared formula. The person asking for help is unsure of how to solve it mathematically and receives a hint to use a different approach. They also discuss the proper order of the point charges and eventually come to a solution using a basic mathematical concept.
phunphysics2
Greetings fellow physics adorers/ mathematicians,

I was wondering if someone could help me with my posted problem. All the necessary details from the template are included in the screenshot on the right.

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From the second attachment (the one on the right) it looks as though you need only cross multiply and solve for x to finish.

I don't know how to do so mathematically...

Your starting formula is wrong.

Draw a picture of the two charges along a line, then equate Coulomb attraction of a unit (positive) test charge to qB to repulsion of that test charge from qA.

Hint: the zero-field point might be between qA and qB, or it might not ...

Coulomb's law is not used. My professor said to only use the E=k[q]/rsquared formula...

I know that the order of the point charges goes as followed

qb -------------------qa--------------------P

phunphysics2 said:
I know that the order of the point charges goes as followed

qb -------------------qa--------------------P

Never mind, you called x the distance from p to qB and d the distance between qA and qB, so what you wrote is fine.

phunphysics2 said:
I don't know how to do so mathematically...

Really?

If ##\frac{a}{b} = \frac{c}{d}## then ##a \cdot d = b \cdot c##

You've never seen this?

## 1. What is the formula for calculating the force between two point charges?

The formula for calculating the force between two point charges is given by Coulomb's Law, which states that the force (F) is equal to the product of the two charges (q1 and q2) divided by the square of the distance (r) between them, multiplied by a constant (k) known as the Coulomb's constant. Mathematically, it can be written as F = (k * q1 * q2) / r^2.

## 2. Can the force between two point charges be negative?

Yes, the force between two point charges can be negative. This happens when the two charges have opposite signs, i.e. one is positive and the other is negative. In this case, the force between them is attractive, pulling the two charges towards each other.

## 3. What happens to the force between two point charges if the distance between them is doubled?

If the distance between two point charges is doubled, the force between them decreases by a factor of four. This is because the force is inversely proportional to the square of the distance between the two charges. So, as the distance increases, the force decreases.

## 4. How does the magnitude of the charges affect the force between two point charges?

The magnitude of the charges has a direct impact on the force between two point charges. As the magnitude of the charges increases, the force between them also increases. This is because the force is directly proportional to the product of the two charges. So, larger charges will experience a stronger force compared to smaller charges.

## 5. Can the force between two point charges be zero?

Yes, the force between two point charges can be zero. This happens when either one or both of the charges are zero, or when the distance between them is infinity. In these cases, there is no force acting between the two charges.

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