Force on a Point Charge in an Electric Field

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Homework Help Overview

The discussion revolves around calculating the force on a negative point charge situated in an electric field created by another negative point charge. The original poster presents a scenario involving two charges: one at the origin and another on the positive x-axis, seeking to understand the force acting on the second charge.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of Coulomb's law and the concept of forces acting on point charges. There is confusion regarding how to isolate the force on one charge versus understanding the interaction between both charges. Questions about the values of constants and variables in the equation are raised.

Discussion Status

Participants are actively engaging with the problem, seeking clarification on the application of Coulomb's law and the symmetry of forces between the two charges. Some guidance has been offered regarding the use of electric fields and the vector sum of forces, but there remains a lack of consensus on the understanding of these concepts.

Contextual Notes

There is an emphasis on understanding the relationship between the two charges and how to apply the relevant equations correctly. The original poster expresses uncertainty about the implications of their notes and the overall setup of the problem.

wheybags
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Homework Statement


A negative point charge of 10 ^(−6 )C is situated in air at the origin of a
rectangular coordinate system. A second negative point charge of 10^(-4) C is
situated on the positive x-axis at a distance of 50 cm from the origin. What is
the force on the second charge?


Homework Equations



Coulomb's law?

The Attempt at a Solution


I don't know ;_;

Coulombs law gives the force between two points, buy I need the force on one of the points. My notes say :
If multiple charges exist, the fore
on anyone charge equals the vector sum of the
forces exerted on it by the other charges.
But I have no idea what that means. Help please?
 
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F = (keq1q2)/r2What your notes say is basically all forces of other charges will affect that one charge.
 
Could you explain how you got that please?
 
wheybags said:

Homework Statement


A negative point charge of 10 ^(−6 )C is situated in air at the origin of a
rectangular coordinate system. A second negative point charge of 10^(-4) C is
situated on the positive x-axis at a distance of 50 cm from the origin. What is
the force on the second charge?


Homework Equations



Coulomb's law?

The Attempt at a Solution


I don't know ;_;

Coulombs law gives the force between two points, buy I need the force on one of the points. My notes say :

But I have no idea what that means. Help please?

hx35 is just reminding you to use Coulomb's law. The two charges are the two charges that you are given in your problem. The force is symmetric between the two charges (the force is equal and opposite on the two charges).
 
berkeman said:
hx35 is just reminding you to use Coulomb's law. The two charges are the two charges that you are given in your problem. The force is symmetric between the two charges (the force is equal and opposite on the two charges).

I don't really get what you mean.
 
wheybags said:
I don't really get what you mean.

Why not?

What is k? What is the value of q1? What is the value of q2? What is the value of r? So what is the force?
 
berkeman said:
Why not?

What is k? What is the value of q1? What is the value of q2? What is the value of r? So what is the force?

I still don't know how to find the force on only one point.
 
wheybags said:
I still don't know how to find the force on only one point.

You are finding the force on both points when you use that equation. The force experienced by each point.

Alternately, you can find the electric field generated by the other point, and use your own charge value as the "test charge" in that electric field at that distance away from the other charge to find the force on you, F=qE. It's the same thing.
 
berkeman said:
You are finding the force on both points when you use that equation.

What? The question asks me to find the force on the second charge.
 
  • #10
wheybags said:
What? The question asks me to find the force on the second charge.

The force on the 2nd charge is the same (but opposite direction) as the 1st charge. There are only 2 charges in this problem, right?

If you have multiple charges in a question, you have to add them up as a vector sum of forces at your test charge location.

Please read the wikipedia article -- hopefully it will help to clear up some of the confusion:

http://en.wikipedia.org/wiki/Coulomb's_law

This force (F) acting simultaneously on point charges (q1) and (q2), is given by

(emphasis is mine)
 

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