RL circuits: Find the voltage through the resistors

[Marcin H]

Homework Statement

Find the voltage through the resistors.

Homework Equations

V=IR
P=IV

The Attempt at a Solution

Am I doing these correctly? Can I find the voltage across the inductor the way I did it?

 

[SammyS]

Homework Statement

Find the voltage through the resistors.

Homework Equations

V=IR
P=IV

The Attempt at a Solution

Am I doing these correctly? Can I find the voltage across the inductor the way I did it?
View attachment 95842

You state that the current through the resistor is zero. Then what is the voltage drop across the resistor?

 

[Marcin H]

You state that the current through the resistor is zero. Then what is the voltage drop across the resistor?

0 volts right? Did I flip those 2 things? I thought inductors after a long time act like wires with no resistance. Is that not true?

 

[SammyS]

0 volts right? Did I flip those 2 things? I thought inductors after a long time act like wires with no resistance. Is that not true?

Yes. zero.

The resistor is in parallel with the inductor, thus it has the same voltage drop. (Can also arrive at this because the inductor has zero resistance.)

 

[Marcin H]

Yes. zero.

The resistor is in parallel with the inductor, thus it has the same voltage drop. (Can also arrive at this because the inductor has zero resistance.)

Ahhh. Ok that makes sense. But then how can we find how much power the current source would supply. P = IV = I^2R = V^2/R. Would we have to discharge the inductor and then use V=IR = (1A)(1000ohms)=1000V?

 

[SammyS]

Ahhh. Ok that makes sense. But then how can we find how much power the current source would supply. P = IV = I^2R = V^2/R. Would we have to discharge the inductor and then use V=IR = (1A)(1000ohms)=1000V?

How do get 1000 ?

Any way you calculate this, you multiply by either the resistance of the inductor, or the voltage drop or some other zero.

 

[Marcin H]

How do get 1000 ?

Woops. I used the wrong equation. I meant to use P = I^2R = (1A)^2*(1000ohms) = 1000V. But is that wrong?

Any way you calculate this, you multiply by either the resistance of the inductor, or the voltage drop or some other zero.

How would I get the resistance of the inductor? Are you talking about the reactance? Xl=wL? And isn't the voltage drop across the inductor 0? I'm not sure how that helps us find the power that the current source is supplying.

 

[SammyS]

Woops. I used the wrong equation. I meant to use P = I^2R = (1A)^2*(1000ohms) = 1000V. But is that wrong?

How would I get the resistance of the inductor? Are you talking about the reactance? Xl=wL? And isn't the voltage drop across the inductor 0? I'm not sure how that helps us find the power that the current source is supplying.

Yes, voltage drop across the inductor is indeed zero. Therefore, V⋅I = ?

 

[Marcin H]

Yes, voltage drop across the inductor is indeed zero. Therefore, V⋅I = ?

Power is 0? How can the power be 0? Does that mean the current source is just off?

 

[SammyS]

Power is 0? How can the power be 0? Does that mean the current source is just off?

no.

simply that to maintain current needs no voltage if there is no resistance.