Lost energy when capacitor discharges

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Homework Help Overview

The discussion revolves around the energy loss observed when discharging a capacitor system consisting of a 1-Farad capacitor and a 9-Farad capacitor. The original poster describes the initial charging of the first capacitor and its subsequent discharge when connected in parallel with the second capacitor, noting a significant loss of energy during this process.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the energy calculations for both states of the capacitor system and question where the lost energy goes. Some discuss the role of resistance in the circuit and its impact on energy loss, while others inquire about the production of electromagnetic radiation during the discharge process.

Discussion Status

Participants are actively engaging with the concepts of energy loss, resistance, and electromagnetic radiation. There are differing interpretations regarding the role of resistance in energy dissipation, and some productive insights have been shared about the nature of oscillations in the circuit.

Contextual Notes

There is an underlying assumption that the setup may not include resistive elements, which is being questioned by participants. The discussion also touches on the implications of connecting capacitors without resistors and the resulting behavior of the circuit.

Tekk
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Homework Statement


[/B]
I have two capacitors: 1-Farad capacitor A, and 9-Farad capacitor B.
In state (a), I charged A with 1 Coulomb of charges, as depicted in figure (a).
In state (b), I paralleled A with B, by doing this I discharged A, as depicted in figure (b).

I try to find the total energy of state (a) and state (b). From what I have calculated, the system lost 90% of its energy when it goes from (a) to (b). Where does the energy go?

Homework Equations



Q=C\phi
U=(1/2)C\phi^2

The Attempt at a Solution


[/B]
Please refer to the image below.
IMG_0050 copy.jpg
 
Last edited:
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Tekk said:
Where does the energy go?
You heat the wires and the capacitors from the resistances in the setup. A tiny bit is also lost to electromagnetic radiation.
 
mfb said:
You heat the wires and the capacitors from the resistances in the setup. A tiny bit is also lost to electromagnetic radiation.

I think my approach to find energy assumes there is no resistance on wires. So I suspect that energy would not turn to heat on these wires.

What I see during the discharge process is a flow of electrons. Can you explain how electromagnetic radiation is produced?
 
Your approach is independent of the resistance.
Connecting capacitors like that without any resistors is a very special case, it will give you an extremely good oscillator (as you always have a small inductance) and all the lost energy will be emitted as radiation over time.
Tekk said:
Can you explain how electromagnetic radiation is produced?
You have a variable current flow = accelerated charges. With small resistances, current will oscillate back and forth for a while.
 

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