J"Calculating Work for Charging a Parallel Plate Capacitor

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Homework Help Overview

The problem involves calculating the work done in charging a parallel plate capacitor to a specific electric potential using a given number of electrons. The subject area includes concepts from electrostatics and energy in capacitors.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between electric potential, charge, and work, with some questioning the appropriateness of the formula used for energy in the context of a changing potential. There are inquiries about converting the charge from electrons to coulombs.

Discussion Status

Some participants have provided alternative perspectives on the formulas applicable to the problem, suggesting the need for a more nuanced approach due to the variable nature of potential as charge accumulates. There is an ongoing exploration of the correct units and calculations.

Contextual Notes

Participants note that the charge is expressed in terms of electrons, which requires conversion to standard units, and there is mention of potential discrepancies in the formulas used for energy calculations.

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Homework Statement



A parallel plate capacitor is changed to an electric potential of 334V by moving 3.78e16 electrons from one plate to the other. How much work is charging the capacitor?

Homework Equations


Delta V= Delta PE/ q
c=q/v


The Attempt at a Solution


Delta V= Delta PE/ q
rearrange to q * PE = 3.78E16 *334= 1.26E19
 
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What fraction of a coulomb is the 3.78*1016 electrons of charge?
 
I don't like the look of your "Delta V= Delta PE/ q" in this case. Due to the fact that the V changes as charge is added to the capacitor, you get a slightly more complicated formula for the energy of the charged capacitor: E = 0.5*Q*V. Roughly speaking, you use the average V so you get a factor of 0.5. Check it out at http://en.wikipedia.org/wiki/Capacitor

Delta V= Delta PE/ q
rearrange to q * PE = 3.78E16 *334= 1.26E19
Here you have rearranged incorrectly. Also, you have entered the charge in non-standard units. The charge is given as a certain number of electron charges, and this number must be multiplied by the charge in Coulombs on one electron.
 
i think i should be the same where 1 j/c is = to 1 Ev, so ur saying the formula can't be done? (E=.5*q*v)
 

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