- #1
giladsof
- 13
- 0
Homework Statement
Homework Equations
U = 0.5CV^2
The Attempt at a Solution
I'm really lost on this one...?
Parallel-plate capacitor with flipping charge
Click For Summary
Homework Help Overview
The discussion revolves around a parallel-plate capacitor and the effects of changing the distance between its plates on the energy in the system. Participants explore the implications of this change and the associated energy calculations.
Discussion Character
- Exploratory, Conceptual clarification, Assumption checking
Approaches and Questions Raised
- Participants discuss the need to calculate the energy before and after changes to the capacitor setup, questioning how to approach the energy calculations and the intuitive understanding of energy dynamics in the system.
Discussion Status
Some participants express confusion regarding the problem and seek clarification on the energy implications of moving the capacitor plates. Others provide guidance on considering the forces involved and the work required to move charges within the electric field.
Contextual Notes
There is mention of homework rules that require participants to show attempts at solutions, and some participants express frustration with the tone of responses while seeking constructive help.
U = 0.5CV^2
I'm really lost on this one...?
- #2
zhermes
- 1,253
- 3
Yes, you do seem to be fairly lost on this one.
Is that the only question you had?
Is that the only question you had?
- #3
giladsof
- 13
- 0
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
But in this problem I don't seem to manage to do so... more help and less sarcastic remarks will be most appreciative
- #4
berkeman
Admin
- 69,479
- 25,003
giladsof said:Homework Statement
Homework Equations
U = 0.5CV^2
The Attempt at a Solution
I'm really lost on this one...?
Do you see intuitively whether it will require energy to be put into the system, or give energy back, to switch the position of the plates? Why?
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).
zhermes said:
I believe he is just gently reminding you of the PF Homework Help rules, which require you to show an attempt at a solution.
- #5
giladsof
- 13
- 0
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?
One small question remains- I don't understand why is it so intuitive that the capacitor will resist this change?
- #6
berkeman
Admin
- 69,479
- 25,003
giladsof said:
Because you're having to move charges against the forces from the E-field. You have to do work to move the charges against those forces. If you were going the other way, well, that's the way the charges would go anyway if they were not constrained to be held on the plates (if they were free charges).