Need help using Coulomb's Law to find unkown charge

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SUMMARY

The discussion centers on applying Coulomb's Law to determine the unknown charge q1 when charge q2 is in static equilibrium. The user initially assumed that q1 and q2 were equal, which is unnecessary. The correct approach involves calculating the forces exerted on q2 by both q1 and the center charge, equating these forces, and solving for q1. This method effectively utilizes the principle that the net force on q2 must equal zero.

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  • Coulomb's Law for electrostatic forces
  • Understanding of static equilibrium in physics
  • Basic algebra for solving equations
  • Concept of force cancellation in a system
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Students studying physics, particularly those focusing on electrostatics and force interactions, as well as educators seeking to clarify concepts related to Coulomb's Law and static equilibrium.

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Hi, the problem states the following. "Charge q2 is in static equilibrium. What is q1?"

I've attached the image of the problem I'm working on. From the looks of this it should be quick and simple it seems, but I am having a tough time with it. I would appreciate any help you can offer.

With q2 being in static eq., I thought that meant that all forces on q2 sum to zero, so I tried to add the forces from q1 and the center charge up and set equal to zero and solve for q1, but I'm not sure if this is right. Also, I put in the assumption that q1 and q2 are equal and I don't know if that is true, either. :cry:
 

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You do not need to assume that q1 and q2 are equal. Basically, you just need to write down the force exerted on q2 by q1 and the center charge respectively. Equate these two expressions and solve for q1.


Kenneth
 
Last edited:
Kenneth,

Thanks for the help. I can't believe I didn't notice that the q2's would cancel when you equate the two. Yikes, I need to get to bed before I do any more damage :zzz:
 

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