# Homework Help: RL circuits: Find the voltage through the resistors

1. Feb 14, 2016

### Marcin H

1. The problem statement, all variables and given/known data
Find the voltage through the resistors.

2. Relevant equations
V=IR
P=IV

3. The attempt at a solution
Am I doing these correctly? Can I find the voltage across the inductor the way I did it?

2. Feb 14, 2016

### SammyS

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

3. Feb 14, 2016

### Marcin H

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?

4. Feb 14, 2016

### SammyS

Staff Emeritus
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.)

5. Feb 14, 2016

### Marcin H

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?

6. Feb 14, 2016

### SammyS

Staff Emeritus
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.

7. Feb 14, 2016

### Marcin H

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.

8. Feb 14, 2016

### SammyS

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

9. Feb 14, 2016

### Marcin H

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

10. Feb 14, 2016

### SammyS

Staff Emeritus
no.

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