Why is one of the solutions obtained using Coulomb's Law not valid?

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Homework Help Overview

The discussion revolves around the application of Coulomb's Law in determining the position of a third charge in relation to two other charges. The original poster presents a scenario involving two charged particles and seeks to understand the validity of one of the solutions obtained from a quadratic equation derived from Coulomb's Law.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to analyze the solutions obtained from a quadratic equation related to the electrostatic forces acting on a third charge. They question the validity of one solution and seek clarification on why it appears to be unphysical.

Discussion Status

Some participants have provided insights regarding the nature of the solutions, particularly focusing on the implications of charge placement and stability. There is an acknowledgment of the potential for quadratics to yield unphysical solutions, but no consensus has been reached on the broader implications of these findings.

Contextual Notes

Participants are exploring the assumptions related to charge placement and the conditions for equilibrium in electrostatic scenarios. The discussion includes a separate inquiry about a different problem involving a charged metal rod and a floating charged ball, indicating a broader interest in Coulomb's Law applications.

Saladsamurai
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[SOLVED] Question about Coulomb's Law

I just solved this a problem in my text: Particle 1 of charge +1.0 uC and particle 2 of charge -3.0 uC are held at a separation L=10.0 cm on an x-axis. If particle 3 of unknown charge q3 is to be placed such that the net electrostatic force on it from 1 and 2 is zero, what must its x and y coordinates be?

Okay, I solved this using Coulomb's Law which gave me a quadratic. Thus, I got two solutions. My question is: why is one of them not valid?

I got x=.0366 and x=-.14. -.14 m is the correct answer. Why does the .0366 work? And if it does not, why did the quadratic produce it?

It may be obvious, but I am just not seeing it now.

Thanks
 
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It's obvious. A charge of either sign placed between two opposite charges will experience a force from both in the same direction. It has to be outside of the region to be in even unstable equilibrium. Quadratics often give an unphysical solution.
 
I knew it had to do with the signs. . . I just couldn't put my finger on it. Thanks Dick! Now I know to look for that.
 


Hello !
Can anyone help me to solve the below problem on Coulomb's law please..
One Metal rod with -1000C charge is hanging on the earth. One another charged metal ball which mass 1 kg is tie by a rope & it floating 1m away from the rod. How much charge is containing by the ball??
 

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