Understanding Electric Force: Calculating Change in Potential Energy

AI Thread Summary
The discussion revolves around calculating the change in potential energy when a charge +q is moved from a distance of 3r to 2r by a charge -q. The initial calculations involve using the work-energy principle and the formula for electric potential energy, resulting in an expression for deltaU. However, confusion arises regarding the interpretation of the potential energy formula and the correct application of the distance in the context of the problem. The participant realizes the mistake in their understanding but indicates that they have encountered another problem related to the topic. The discussion highlights the complexities of electric force and potential energy calculations in electrostatics.
soljaragz
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Here is the question that I have no idea what is happening

"What is the change in potential energy of a particle of charge +q that is brougt from a distance of 3r to a distance of 2r by a particle of charge -q? "

Here's what I tried

-W = deltaU
W = qEd
W = (kq1q2/r^2) d
d= 3r - 2r = r

substituting I get
W = kq1q2/r
so deltaU = -kq1q2/r.....im correct up to here, but its not the final answer according to the book,...the explanation then shows some weird things that I don't understand.

but isn't the question asking for change in potential
so shouldn't deltaU (-kq1q2/r) be the answer?
 
Last edited:
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Hint: The potential energy of two charges separated by a distance r is given by kq1q2/r (where the zero level is taken to be at r = infinity).
 
[nvm i get it now]
I have another problem though
 
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