Finding the Force Between Two Point Charges

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Homework Help Overview

The discussion revolves around calculating the force between two point charges, specifically a +5μC charge and a -100μC charge, separated by a distance of 15 cm. The participants are exploring the implications of the force calculated using Coulomb's law.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the interpretation of the force between two charges, questioning the notion of adding forces exerted by each charge on the other. There is an exploration of the relationship between the forces and the net force in the system.

Discussion Status

The discussion is active, with participants examining different interpretations of the force between the charges. Some guidance has been offered regarding the nature of the forces involved, but there is no explicit consensus on the interpretation of the problem.

Contextual Notes

Participants are considering the implications of the calculated force and the definitions involved in describing the interaction between the two charges. There is a focus on the potential confusion surrounding the terms used in the problem statement.

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Homework Statement



Two point charges with charges of +5μC and -100μC are separated by 15 cm. The magnitude of the force between these charges is:

a) 1.99 N
b) 4.02 N
c) 20 N
d) 199 N
e) 400 N

Homework Equations



F = q1q2 * k / r^2

The Attempt at a Solution



F = (9.00*10^9)(5.0*10^-6 C)(1.0*10^-4 C) / (0.15 m)^2

F = 4.5 / 0.0225 m^2

F = 200 N

Why is it incorrect to think the force of one on two is 200 N and the force of two on one is 200 N so the force between them is 400 N?
 
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The phrase "force between two charges" is kind of fuzzy. It just means to find the force that one particle exerts on the other. The other particle will then exert the same magnitude of force on the first particle but in the opposite direction. [If for some reason you decided to add these two force vectors, what would you get?]
 
Aha! 0 N. (right?)
 
Right! The net force for the system is zero. Good. But the answer to the question "what is the magnitude of the force between them" would be "200 N". At least that's my interpretation!
 

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