How Does Inductance Affect a DC Circuit?

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Homework Help Overview

The discussion revolves around a DC circuit involving an inductor and a resistor, focusing on the effects of inductance on circuit behavior. Participants are tasked with determining various parameters such as time constants and voltage drops across components.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of the time constant using the formula t = L/R, with some uncertainty regarding subsequent voltage drop calculations. There is also exploration of how to determine the resistance of a new inductor based on the time constant.

Discussion Status

Some participants have successfully calculated the time constant and are seeking clarification on voltage drops and resistance. There is an ongoing exploration of how the total resistance in the circuit is affected by the addition of the new inductor.

Contextual Notes

Participants are working under the constraints of homework rules, which may limit the information they can use or the methods they can apply. There is a focus on understanding the relationships between inductance, resistance, and time constants without providing direct solutions.

debreets
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An inductor of negligible resistance and an inductance of 0.2 H is
connected in series with a 330 Ω resistor to a 12V d.c. supply.
Determine:
(a) the time constant of the circuit
(b) the voltage drop across the inductor after two time constants
(c) the voltage drop across the resistor after three time constants
(d) the resistance of a 0.2 H coil used to replace the inductor if the
circuit’s time constant falls to 0.55 ms.

I have answer a) using formula t = L/R L is 0.2 and R being 330, t giving 0.0006 seconds ( or 0.6 ms )
Im unsure of b) and c) but will spend time on those shortly.
Part d) looked simular to a) I thought maybe use the same formula (t=L/R) but make R the subject, that would be R=t/L.
I plugged in 0.00055 for t and 0.2 for L, giving an answer of 363.63? time was given as 0.55 ms so converted to seconds giving 0.00055.
Am I on the right track or have I gone wrong?
 
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debreets said:
I know this is an old thread but I am struggling also, I have answer a) using formula t = L/R L is 0.2 and R being 330, t giving 0.0006 seconds ( or 0.6 ms )
Im unsure of b) and c) but will spend time on those shortly.
Part d) looked simular to a) I thought maybe use the same formula (t=L/R) but make R the subject, that would be R=t/L.
I plugged in 0.00055 for t and 0.2 for L, giving an answer of 363.63? time was given as 0.55 ms so converted to seconds giving 0.00055.
Am I on the right track or have I gone wrong?

They are asking for the resistance of a new inductor if it has the same inductance and it is put in series with the 330 Ohm resistor. So, you have a number that is on the way to getting the right answer.
 
Thanks for your reply,
I'm confused as I believe iv worked out the resistance of the inductor at 363.63 ohms, so would the resistance of the coil not be the same?
 
debreets said:
Thanks for your reply,
I'm confused as I believe iv worked out the resistance of the inductor at 363.63 ohms, so would the resistance of the coil not be the same?

No, because this new circuit is still factoring in the 330 Ohm resistor that is connected when you are calculating the total resistance.
 
Ok, so, 363 (reistance of ciruit) - 330 (resistance of resistor in circuit) = 33 ohm (resistance of coil)
Think iv got it now,
Thanks for your help
 

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