Troubles with a circuit analysis situation (RLC circuit)

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Discussion Overview

The discussion revolves around analyzing an RLC circuit, specifically focusing on the voltage across a 2 Ω resistor at different time intervals (t = 0+ and t = 0-). Participants explore the implications of steady state conditions and the behavior of circuit elements at these moments.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants seek clarification on whether the question pertains to the voltage across the 2 Ω resistor at time t = 0+ or t = 0-.
  • It is noted that at t = 0-, there is no current supplied by the current source, leading to the conclusion that the current through the resistor is also zero.
  • One participant calculates the voltage across an open circuit using Kirchhoff's Voltage Law (KVL), suggesting that the capacitor voltage is -20 volts.
  • Another participant agrees that at steady state, the potential difference across the inductor must be zero, reinforcing the relationship between the voltage source and capacitor voltage.

Areas of Agreement / Disagreement

Participants generally agree on the behavior of the circuit elements at t = 0- and the implications for current and voltage. However, there are nuances in the interpretations of the voltage calculations and the conditions under which they apply.

Contextual Notes

Limitations include the need for clarity on the definitions of time intervals and the assumptions regarding steady state conditions. The discussion does not resolve all mathematical steps or the implications of the calculated voltages.

Anti Hydrogen
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Homework Statement
the book doesn't explain how they calculated the initial value of the voltage of the 2 ohms resistance and the inductor current; i understand, however, how they calculated the initial value of the capacitor. i think they are taking the voltage of the open circuit in left as zero so that the voltage of resistance takes the value of zero too; if so, why is the open circuit voltage zero?, the definition of open circuit according to the book says that voltage of a open circuit can be any value. note that the open circuit in the left of the circuit comes from a singularity funtion
Relevant Equations
please any help will be appreciated!
thanks
 

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Hi Anti Hydrogen,

It's not entirely clear to me what you're asking. Is it for the voltage across the 2 Ω resistor at time t = 0+ ?
 
gneill said:
Hi Anti Hydrogen,

It's not entirely clear to me what you're asking. Is it for the voltage across the 2 Ω resistor at time t = 0+ ?
it is at t=0 minus
 
gneill said:
Hi Anti Hydrogen,

It's not entirely clear to me what you're asking. Is it for the voltage across the 2 Ω resistor at time t = 0+ ?
it is the initial value, this is, at t less than 0
 
Okay. Well, at t= 0- there's no current being supplied by the current source, and no current due to the voltage source either (at steady state the capacitor looks like an open circuit). So, no current flowing anywhere. What does that tell you about the current through that resistor?
 
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it's zero too, hence, the voltage across it is zero?
 
Anti Hydrogen said:
it's zero too, hence, the voltage across it is zero?
Yup.
 
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.
gneill said:
Yup.
i calculated the voltage across the right open circuit applying the KVL in right mesh,
-20-vc=0
then
vc=-20
im i right?
 

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Yes. At steady state the capacitor must have a potential difference that satisfies the KVL around the loop, but more obviously, since there's no current change through the inductor the potential at the top of the inductor with respect to the bottom of the inductor must be zero. Hence the sum of the voltage source and capacitor voltage must be zero.
 
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