Resolving Inductance Issues: 0.2H Coil Resistance Calculation

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Homework Help Overview

The discussion revolves around calculating the resistance of a coil with an inductance of 0.2H in the context of a circuit's time constant, which is specified to be 0.55ms. Participants are exploring the relationship between inductance, resistance, and time constant in an electrical circuit.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants are attempting to derive the resistance using the formula for time constant (L/R) and are discussing the implications of the values provided. Some are questioning the representation of the time constant and the calculations involved.

Discussion Status

The discussion includes various attempts to clarify the problem and correct earlier misrepresentations of the time constant. Some participants are providing calculations and checking assumptions about the circuit configuration, but there is no explicit consensus on the final resistance value.

Contextual Notes

There are indications of confusion regarding the correct interpretation of the time constant and the values used in calculations. Participants are also addressing the setup of the circuit, including the presence of a resistor in series with the inductor.

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Homework Statement


Determine the resistance of a 0.2H coil used to replace the inductor if the circuits time constant falls to 0.55ms.


Homework Equations


l/R


The Attempt at a Solution

L/R = 0.2H/R = 0.55ms
Transposing for R... R = 0.2/0.0055 = 36.36Ω is the resistance of the coil?
 
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Your English is not good so I don't know exactly what the problem is.

If it's to find the value of R in series with a pure inductor of L = 0.2H to give a time constant of 0.55 ms then your formula is right but you misrepresented 0.55 ms.
 
Sorry i failed to submit all the question. Here it is: An inductor of negligible resistance and an inductance of 0.2H is connected in series with a 330Ω resistor to a 12 d.c supply. Determine the resistance of a 0.2H coil used to replace the inductor if the circuits time constant falls to 0.55ms.

yep got my powers wrong. So it will be 0.2/0.00055 = 3.6Ω?
 
You have a perfect inductor L of 0.2H in series with R1 = 330 ohms and R2 with unknown resistance (to be solved).

What is the time constant of this configuration as a function of L, R1 and R2? L, R1 and the numerical time constant are known. Solve for R2.
 
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R= 0.2/0.00055 = 363Ω is total resistance.

resistance - 330Ω = 33.6Ω is coil resistance when the circuits time constant falls to 0.55mS?
 
brenfox said:
R= 0.2/0.00055 = 363Ω is total resistance.

resistance - 330Ω = 33.6Ω is coil resistance when the circuits time constant falls to 0.55mS?

Right!
 
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