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Parallelplate capacitor with flipping charge 
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#1
Jun1911, 05:22 AM

P: 13

1. The problem statement, all variables and given/known data
2. Relevant equations U = 0.5CV^2 3. The attempt at a solution I'm really lost on this one...? 


#2
Jun2111, 03:17 PM

P: 1,261

Yes, you do seem to be fairly lost on this one.
Is that the only question you had? 


#3
Jun2111, 06:52 PM

P: 13

well usually in these kind of questions where there is some kind of change in the capacitor (the plates were move closer for instance) We need to calculate the energy in the system before the change, calculate the energy afterwards and see the change's size and sign.
But in this problem I don't seem to manage to do so.... more help and less sarcastic remarks will be most appreciative 


#4
Jun2111, 07:12 PM

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P: 41,085

Parallelplate capacitor with flipping charge
And to calculate it, I think I would just calculate the energy required to move the charges those distances in that Electric Field. What is the equation for the force on a charge in an Electric Field? What is the equation for the work done by a force through a distance? Don't forget to account for each plate's charge separately (so two energy calculations). 


#5
Jun2511, 05:39 AM

P: 13

Thank you I solved it.
One small question remains I don't understand why is it so intuitive that the capacitor will resist this change? 


#6
Jun2511, 11:09 AM

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P: 41,085




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