Calculating Charge Using Coulomb's Law

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    Coulomb's law Law
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Homework Help Overview

The problem involves calculating the value of an unknown charge using Coulomb's Law, given a specific force between two charges and the distance separating them. The context is centered around electrostatics and the application of the formula for electric force.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of Coulomb's Law and the correct interpretation of the formula, particularly focusing on the squaring of the radius. Questions arise regarding the accuracy of calculations and the signs of the charges involved.

Discussion Status

The discussion is ongoing with participants verifying calculations and correcting assumptions. Some guidance has been provided regarding the mathematical approach, and there is an acknowledgment of potential errors in the original calculations. Multiple interpretations of the results are being explored.

Contextual Notes

There is mention of discrepancies between the calculated value and the expected answer from the textbook, prompting further investigation into the mathematical process used. Participants note the challenge of managing complex calculations in a single step.

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Homework Statement


When a -9.0 micro-coulomb charge is placed 0.12 cm from a charge q in a vacuum, the force between the 2 charges is 850 N. What is the value of q?


Homework Equations


F = kq1q2/r2


The Attempt at a Solution


q2 = Fr2/kq1
q2 = (850 N)(0.0012 m2)/(9.00 x 109 Nm2/C2)(-9.00 x 10-6 C)
q2 = -1.22 x 10-18 C

My question is am I doing this right? The answer that my book gives is 1.5 x 10-8 C.
 
Last edited:
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It's radius squared right?
 
Feldoh said:
It's radius squared right?

Yes it is sorry I corrected my work above! Thanks!
 
Well since you now (correctly) squared the radius, what do you get as an answer?
 
Feldoh said:
Well since you now (correctly) squared the radius, what do you get as an answer?

The answer that I get is -1.22 x 10-18 C. When I worked the question I had squared the radius.
 
Last edited:
Well, the answer I get is the same one your book gives, so you're probably doing something wrong with the math. I'm not sure where that 10-18 is coming from...
 
Thanks for all your help! It was me trying to put too much info into my calculator at once. If I break it up figure out the top then figure the bottom and divide I get the right answer except mine is negative.

Thanks again!
 

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