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

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

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= 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.


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