Electric field problem -- Repulsive force between two charged spheres

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Homework Help Overview

The discussion revolves around an electric field problem involving the repulsive force between two charged spheres, particularly focusing on the changes in force after the spheres touch and then separate.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants explore the implications of the spheres touching and the subsequent equalization of charge. Questions arise regarding the original charges of the spheres and the conditions under which the problem is set, including the size of the spheres.

Discussion Status

There is an ongoing exploration of the factors affecting the force between the spheres, with some participants questioning the assumptions made about charge distribution and the specifics of the problem setup. Guidance on calculating average charge has been provided, but no consensus on the original charges has been reached.

Contextual Notes

Participants note the lack of specification regarding the size of the spheres, which may affect the charge distribution and the overall interpretation of the problem.

Dezzi
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Homework Statement
Two identical spheres have charges q1 and q2. When they are 20 cm apart, the replusive force between them is 1.35×10^‐4N. After they touched together and separated once again to 20cm, the replusive force between them is 1.406×10^-4N. FIND q1 and q2. (Ans 20nC; 30 nC)
Relevant Equations
F=kQ1Q2/r^2
I attempt to solve the problem in the picture below.
 

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Why is the force different the second time?
 
PeroK said:
Why is the force different the second time?
The question say " they touched together and separated once again"
 
Dezzi said:
The question say " they touched together and separated once again"
So, what changed?
 
PeroK said:
So, what changed?
I guess the charges get equalised. So, you've worked out that average charge: ##2.5 nC##, which looks right.

The hard bit is to figure out what the original charges were. Any ideas?
 
A quibble: since the spheres are evidently conductors, the question ought to specify that the spheres are much smaller than 20cm radius. Otherwise the charge distributions complicate matters.
 
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