Power dissipation in parallel circuit

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Discussion Overview

The discussion revolves around the power dissipation in a parallel circuit with two resistors, focusing on the relationship between current, resistance, and power. Participants explore the implications of minimizing power loss and the conditions under which currents are distributed in the circuit.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents a calculation suggesting that the power dissipated in a parallel circuit can be minimized, leading to the condition I1R1 = I2R2.
  • Another participant challenges this by stating that if the currents I1 and I2 are changing, the resistances should also change, as the total current I is constant.
  • Some participants argue that the voltage across parallel circuit elements is the same, implying that I1R1 = I2R2 is a trivial result.
  • There is a mention of the "shakedown theorem" as a relevant principle in the context of energy dissipation.
  • One participant suggests that the discussion should focus on minimizing energy dissipation rather than strictly adhering to Kirchhoff's voltage law.
  • Another participant expresses confusion about the constancy of resistance while currents change, seeking clarification on this point.
  • Some participants assert that Bruce's derivation maintains Kirchhoff's current law but may violate Kirchhoff's voltage law.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between current and resistance in parallel circuits, with no consensus reached on the implications of minimizing power dissipation or the validity of the calculations presented.

Contextual Notes

There are unresolved assumptions regarding the constancy of resistances and the application of Kirchhoff's laws in the context of varying currents. The discussion also touches on the implications of energy dissipation in steady-state conditions.

  • #31
K^2 said:
But yeah, it makes perfect sense. Let's say the circuit runs for some time τ. Some quantity of charge q has flown through it. The total energy dissipated is ∫Vdq = ∫Pdt. What would it mean for power to be unoptimized? It would mean that one of these elements dq would be able to find a path through your circuit with lower V. That would mean that different branches have different voltages. So the solution must certainly be a minimum in P in a steady state circuit.
I'm sorry, but I don't fully understand what you're saying here. It sounds (to me) like you're saying that unoptimised power means that there is more than one possible value for the power dissipated by a charge element going through the circuit. But I don't see why this is necessarily true?

And for clarity to anyone who was wondering, the optimisation of power which I wrote in my first post is done by keeping the resistances constant, and the total current constant. And varying the currents through each resistor, while keeping to the constraint that the currents 'add up' at a node.

I've been thinking about this for aaages, but I still can't think of the reason behind why this happens.
 
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  • #32
It is interesting to notice this method works only with resistors.
It does not work with a circuit containing diodes and resistors !
Such a method would lead to a minimized dissipated power but voltages are not the same between to voltage nodes (try it with a diode and a resistor in parallel!).
I am curious to find out why...

If somebody has an idea...
 

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