Solving Inductor 12 Henry Discharge: R Calculations

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SUMMARY

The discussion focuses on calculating the resistance of a resistor in a circuit with a 12 Henry inductor during discharge. The relevant equation is I = I₀e^(-R/L)t, where I₀ is the initial current. The challenge arises from determining the final current, which approaches zero but is undefined in logarithmic calculations. Participants suggest using a practical time constant approach, typically considering the current to be effectively zero after approximately 5τ, where τ = L/R.

PREREQUISITES
  • Understanding of inductor behavior in electrical circuits
  • Familiarity with the exponential decay formula I = I₀e^(-R/L)t
  • Knowledge of time constant calculations in RL circuits
  • Basic logarithmic functions and their applications in physics
NEXT STEPS
  • Research the concept of time constants in RL circuits
  • Study the practical applications of the equation I = I₀e^(-R/L)t
  • Explore methods for determining effective current thresholds in discharge scenarios
  • Learn about the implications of using approximations in electrical engineering calculations
USEFUL FOR

Electrical engineering students, circuit designers, and anyone involved in analyzing inductor discharge behavior in practical applications.

georgedaisuki
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Homework Statement


Inductor 12 Henry, energy supply is Emf knot.

At t=0, the switch is opened which leads to rapid discharge along a resistor. The flash from the discharge lasted 50 ms. What is the resistance of the resistor?


Homework Equations


I know to use i=Ie^(-R/L) t but what would I use for the final current since it goes to zero?

Ln 0 is undefined.


The Attempt at a Solution



I thought it would be enough to say the final current is .0000001 and the initial current is 1. But taking ln of the final current gives many different numbers depending on accurate you make the initial current. Is there a better way to solve this>?
 
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Well ideally it takes an infinite amount of time for the current to drop to 0 A. But in reality it is usually some factor of the time constant. Does your book mention something about how long it takes for the current to be considered 0 A? For example, 5\tau. Where:

\tau = L/R
 

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