Applying Kirchoff's Law in an R-L circuit with parallel resistors

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SUMMARY

This discussion focuses on applying Kirchoff's Law in an R-L circuit with parallel resistors. Participants clarify the behavior of the circuit after a switch is opened, emphasizing that for a DC current, an inductor behaves like a wire, rendering the right resistor irrelevant in steady-state conditions. The correct formula for calculating current through the inductor before the switch is opened is confirmed as I = V/R, where V is 55 volts and R is 150 ohms, resulting in a current of 0.3667 A.

PREREQUISITES
  • Understanding of Kirchoff's Laws
  • Basic knowledge of R-L circuits
  • Familiarity with DC circuit analysis
  • Ability to perform Ohm's Law calculations
NEXT STEPS
  • Study the behavior of inductors in DC circuits
  • Learn about parallel resistor configurations in R-L circuits
  • Explore transient analysis in R-L circuits
  • Investigate the implications of switch operations in electrical circuits
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Electrical engineering students, circuit designers, and anyone interested in understanding R-L circuit dynamics and the application of Kirchoff's Law.

amolv06
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Assume that the switch has been closed a long time.

1.) Find the current through the inductor before the switch is opened.
2.) Find the voltage in the right resistor before the switch is opened.
3.) Find the current in the right resistor right after the switch is closed.

My question here is how do you treat both resistors? My hunch tells me that the right resistor is irrelevant, and that loop should be treated as superfluous, but I'm not sure. If anyone could answer that question, I would greatly appreciate it. Thanks.
 
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I think 3.) should end in "After the switch is opened".

For a DC current, an inductor is just a wire. This makes the exact value of the right resistor indeed irrelevant.

for 3.) I can't say that the right loop is irrelevant. What happens to the current in the inductor right after you close the switch? where will this current now go?
 
Thanks, I completely mistyped that. 3 should read opened rather than closed.

Just to clarify, the answer to #1 then should look like the following?

\frac{V}{R} = I where I is 55/150?
 
Last edited:
Thanks, I completely mistyped that. 3 should read opened rather than closed.

Just to clarify, the answer to #1 should be:

I=V/R where I = 55/150?
 
amolv06 said:
Thanks, I completely mistyped that. 3 should read opened rather than closed.

Just to clarify, the answer to #1 should be:

I=V/R where I = 55/150?

Yes, that is the answer
 

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