How to calculate energy stored in a parallel-plate capacitor?

  • Thread starter Thread starter ajmCane22
  • Start date Start date
  • Tags Tags
    Capacitor
Click For Summary

Homework Help Overview

The problem involves calculating the energy stored in a parallel-plate capacitor with specific dimensions and voltage conditions. It includes determining the energy for two different plate separations and the work required to change the separation.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the use of the capacitor energy formula and question the consistency of results between different parts of the problem. There is a focus on understanding how changes in plate separation affect voltage, charge, and capacitance.

Discussion Status

Participants are actively exploring the relationships between charge, capacitance, and voltage as they relate to the energy stored in the capacitor. Some guidance has been provided regarding the constancy of charge and the change in voltage with plate separation.

Contextual Notes

There is uncertainty regarding the calculations for parts (b) and (c), and participants are questioning the assumptions made about the relationships between the variables involved.

ajmCane22
Messages
33
Reaction score
0

Homework Statement



A parallel-plate capacitor has plates with an area of 383 cm2 and an air-filled gap between the plates that is 1.51 mm thick. The capacitor is charged by a battery to 575 V and then is disconnected from the battery.
(a) How much energy is stored in the capacitor?

(b) The separation between the plates is now increased to 4.53 mm. How much energy is stored in the capacitor now?

(c) How much work is required to increase the separation of the plates from 1.51 mm to 4.53 mm?
Please, explain your reasoning.


The Attempt at a Solution



This is what I did:

C = εA/d to find C and then used E = 1/2CV^2 to find E. Then for part (c) I subtracted the value for part (b) from the value for part (a). I got the following values:
(a)3.712e-5 J
(b)1.236e-5 J
(c)2.476e-5 J

(b) and (c) are incorrect and I'm not sure what I'm doing wrong. (a) and (b) should be the same equation, correct? I don't understand why I'm getting part (a) right and part (b) wrong. Please help.
 
Physics news on Phys.org
ajmCane22 said:
(b) and (c) are incorrect and I'm not sure what I'm doing wrong. (a) and (b) should be the same equation, correct? I don't understand why I'm getting part (a) right and part (b) wrong. Please help.
When the plates are separated by some additional distance, which of the quantities Q, C, V remain the same and which ones change?
 
Oh! The voltage changes, so I need to calculate the second voltage, right?
 
Yes, the voltage changes but the charge remains the same.
 

Similar threads

Charge upon a parallel plate capacitor
  • · Replies 18 ·
Replies
18
Views
3K
Comparing energy lost by the battery & energy gained by the capacitor.
  • · Replies 5 ·
Replies
5
Views
2K
Ranking charge stored on three capacitors by a battery
  • · Replies 6 ·
Replies
6
Views
3K
Capacitance of a Parallel Plate Capacitor
  • · Replies 28 ·
Replies
28
Views
3K
Capacitor Questions Charging and Discharging
  • · Replies 4 ·
Replies
4
Views
4K
Energy stored in parallel plate capacitor
  • · Replies 2 ·
Replies
2
Views
2K
Removing The Dielectric From A Parallel Plate Capacitor
  • · Replies 4 ·
Replies
4
Views
5K
Capacitors charged in parallel
  • · Replies 3 ·
Replies
3
Views
2K
Two capacitors in parallel: potential difference/energy
  • · Replies 5 ·
Replies
5
Views
4K
Capacitance and Dielectrics in Parallel Plate Capacitors
  • · Replies 2 ·
Replies
2
Views
2K