RL circuits - finding resistance and inductance

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Homework Help Overview

The discussion revolves around analyzing an RL circuit in preparation for an exam. The original poster is attempting to determine the resistance and inductance values based on given parameters and equations.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are exploring the implications of the current through the inductor and its behavior at the moment the switch is closed. There are questions regarding the definitions of symbols used in the equations and the methods being applied.

Discussion Status

Some participants have offered guidance by prompting the original poster to clarify the meaning of certain variables and to consider the behavior of the circuit at specific moments. Multiple interpretations of the approach to solving the problem are being explored, particularly regarding the use of Thevenin's theorem.

Contextual Notes

There is an emphasis on understanding the initial conditions of the circuit and the definitions of terms such as time constant and open circuit voltage. The original poster expresses uncertainty about their logic and the next steps in their analysis.

Cocoleia
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Homework Statement


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I am practicing questions from the book in preparation for an exam, and I am having trouble with this one

Homework Equations

The Attempt at a Solution


According to my professor, the answers are: R1=12ohm, R2=9ohm, L=34.28 H
So far this is what I have done:
Voc = 6V
τ = 20/7
Vo = 3V
Rt=7L/20
Rt=6/(-24+Isc(R2+3)
This is just from analyzing the equation that was given in the question. I don't know if my logic is correct, and I am not sure what the next steps will be.
 
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Start with your equation for v(t). What is its value when t equals 0?

Since the current through L can't change instantaneously, prior to closing the switch, what is the current flowing in the circuit? That is the same current that flows through the 3 ohm resistor, so the v(0) value should help.

See if this helps any.
 
Heed @magoo's clues. The important thing here is to note that the current through the inductor doesn't (or can not) change instantaneously, but voltage across it can.
 
Cocoleia said:
Voc = 6V
τ = 20/7
Vo = 3V
Rt=7L/20
Rt=6/(-24+Isc(R2+3)
What do these symbols (Rt, τ, Voc) stand for? Which method are you using?

Given the voltage equation, what will be the equation of current for t>0?
 
cnh1995 said:
What do these symbols (Rt, τ, Voc) stand for? Which method are you using?

Given the voltage equation, what will be the equation of current for t>0?
τ is the time constant
Voc is open circuit voltage
and Rt is thevenin equivalent resistance
(I think)
 
Cocoleia said:
τ is the time constant
Voc is open circuit voltage
and Rt is thevenin equivalent resistance
(I think)

You need not use Thevenin for this circuit.
What is the current through the circuit at t=0+?
 

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