# Got challenged by teacher, Coulomb's Law. (1 Viewer)

### Users Who Are Viewing This Thread (Users: 0, Guests: 1)

#### yasu7

This may not be a challenge for some of you, but it is hard for me as I just got introduced to the topic, your help will be appreciated.
It is about Electric Force. Coulomb's Law.

1. The problem statement, all variables and given/known data
Charges of -1 micro coulomb and -4 microcoulomb are placed at opposite ends of a meter ruler. Where on the ruler could...
(a) a free electron be placed and be in electrostatic equilibrium?
(b) a free proton be placed and be in electrostatic equilibrium?

2. Relevant equations
F=K(q1q2)/r2

F= Force (Newtons)
Q= Coulombs charges
R= distance between the charges
K= botlzmann constant

3. The attempt at a solution

I tried getting the answer by doing math without involving phyisics, like this:

If 4 microcolombs is 100%
then 1 microcoulomb might be 25%
and I have a 1 meter long ruler,
then the new coulomb would be placed 25% to the right from the force that has 1 microcoulomb. That would be 25 cms to the right from the -1 microcoulomb

I reach this conclusion by math logic, but I believe it's wrong and my teacher told me it really is wrong, my method is ambiguous so..

I hope someone helps me get me the correct answer.

#### LowlyPion

Homework Helper
Welcome to PF.

You would be better served to set it up algebraically, where

X = distance to one charge and 1 - X = distance to the other.

Since you want the forces to be equal at that point ... then set them equal and solve for X.

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving