What is the Work Required to Increase Separation of a Parallel Plate Capacitor?

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Homework Help Overview

The discussion revolves around calculating the work required to increase the separation of an isolated parallel-plate capacitor, given its charge and initial capacitance. The problem involves concepts from electrostatics, specifically capacitance and potential energy in capacitors.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore various formulas related to capacitance and energy, questioning the relationships between capacitance, distance, and energy. Some express confusion over the correct equations to use and the implications of changing plate separation.

Discussion Status

The discussion is active, with participants sharing their calculations and questioning each other's methods. Some have offered alternative approaches and highlighted potential errors in reasoning, while others seek clarification on the relationships between capacitance and energy.

Contextual Notes

There is a noted confusion regarding the correct values and relationships in the formulas being used, particularly concerning the area of the plates and the effect of distance on capacitance. Participants are also grappling with the implications of their calculations on the final work done.

  • #31
sw1mm3r said:
thats the formula i was talking about

c2=(3.1x10^-11 F)/3 doesn't give you c2=8.26x10^-12F.
 
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  • #32
no look c1/c2=d2/d1

(3.1x10^-11)/c2=.0045/.0012

c2=8.26x10^-12 so c2 is obviously not c1/3
 
  • #33
OOhhhh. You are talking about c2=(1.2/4.5)*c1. The 1.2 was a typo. There's no '1.2' in the problem anywhere. I apologize for that. It should have been 1.5. You really haven't understood anything of this, have you?
 
  • #34
1.2 is in the problem its 1.2 mm... and i have understood a good chunk of stuff i just got confused on the last part
 
  • #35
Hah. You're right. I substituted the 1.5 for 1.2 way back. Apparently I'm the one who's confused. 34 posts and you lose track. Sorry again. I think you've got it right.
 
  • #36
damn and i was tryin to figure out where i went wrong... kool sounds good i understand it then
 
  • #37
sw1mm3r said:
damn and i was tryin to figure out where i went wrong... kool sounds good i understand it then
I will rewrite my post.
C1 = εοA/d1
In the second case
C2 = εοA/d2

C1/C2 = (εοA/d1)/(εοA/d2)
= d2/d1
Substitute the values of d1, d2 and C1, and find the value of C2.
Using the formula for energy, find the energies in C1 and C2 and find the difference.
 
  • #38
That's perfect. Sorry again if my false recollection that one of the d's was 1.5mm instead of 1.2mm was what was throwing you off. Oh, that's you rl.bhat, thought is was sw1mme3r. Maybe time to quit while I'm not too far behind.
 
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