# Inductor resistor phasor help

1. Mar 1, 2006

### teng125

v(rt) = 125mV cos (wt + 60)
R=250 ohms
L = 250mH
find i(t)
in the circuit there is a inductor in series wif the resistor

may i know why is it the inductor not using to form z and then only divide by v(rt) ??why only the resistor??

2. Mar 1, 2006

### Staff: Mentor

The resistor impedance is 'real', i.e. voltage and current are in phase. The inductor and capacitor each have reactance or 'complex' impedance. i.e voltage and current are out of phase.

3. Mar 1, 2006

### teng125

so when only the inductor will be included??

4. Mar 1, 2006

### Staff: Mentor

Last edited: Mar 1, 2006
5. Mar 1, 2006

### teng125

yes,it is from the book

6. Mar 1, 2006

### teng125

for z = 250 + j250 since w=1000 right??
then v(rt) = 125mV cos (wt + 60)

so can i divide them (v/z) ??

7. Mar 1, 2006

### Staff: Mentor

Ah, I think I now understand what's going on here! I apologize for the confusion.

Looking at the voltage v(rt) = 125mV cos (wt + 60)

I think that should be vR(t) = 125mV cos (wt + 60), which is the voltage across the resistor.

Then the current must be i(t) = vR(t)/R, and because the inductor and resistor are in series, the same current MUST pass through both.

Now the voltage across the resistor AND inductor is

v(t) = vR(t) + vL(t) = i(t) R + i(t) * jwL.

8. Mar 1, 2006

### teng125

oo...okok thanx