Easy electro charge question, calculation error?

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SUMMARY

The discussion centers on a physics problem involving two point charges with a total charge of +11μC, separated by 2.9 cm, experiencing a force of 194 N. The participants used the formula F = KqQ/r² and the constraint q + Q = 11μC to derive the charges. A calculation error was identified regarding the units of charge, which should be in microcoulombs rather than coulombs. The incorrect results of Q = 11 and Q = 1.6 x 10^-12 were attributed to this oversight.

PREREQUISITES
  • Understanding of Coulomb's Law (F = KqQ/r²)
  • Knowledge of charge units, specifically microcoulombs (μC)
  • Ability to solve quadratic equations
  • Familiarity with basic electrostatics concepts
NEXT STEPS
  • Review the principles of Coulomb's Law and its applications
  • Learn how to convert between different units of charge, particularly microcoulombs and coulombs
  • Practice solving quadratic equations in the context of physics problems
  • Explore the implications of attractive and repulsive forces in electrostatics
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in mastering electrostatics and charge interactions.

Paulkaryote
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Homework Statement



The sum of two point charges is + 11μC. When they are 2.9 cm apart, each experiences a force of 194 N. Find the charges given that the force is:
(a)Repulsive
(b)Attractive
(In microNewtons)

Homework Equations


F = KqQ/r^2
q + Q = Net charge

The Attempt at a Solution


I confirmed this with my friend and he got the same answer as me, so maybe we are both making the same mistake.

q + Q = 11 => q = 11 - Q
F = kq(11-Q)/r^2 => 194 = (9x10^9)(11-Q)Q/(0.029)^2
After solving and simplifying the quadratic I got Q = 11 and 1.6*10^-12 which is wrong.
 
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Paulkaryote said:

Homework Statement



The sum of two point charges is + 11μC. When they are 2.9 cm apart, each experiences a force of 194 N. Find the charges given that the force is:
(a)Repulsive
(b)Attractive
(In microNewtons)

Homework Equations


F = KqQ/r^2
q + Q = Net charge

The Attempt at a Solution


I confirmed this with my friend and he got the same answer as me, so maybe we are both making the same mistake.

q + Q = 11 => q = 11 - Q
F = kq(11-Q)/r^2 => 194 = (9x10^9)(11-Q)Q/(0.029)^2
After solving and simplifying the quadratic I got Q = 11 and 1.6*10^-12 which is wrong.

Welcome to PF, Paulkaryote.

What happened to the units attached to the charge? They were not Coulombs, but microcoulombs.
 

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