# Calculating Voltage Drop in an AC circuit

1. Sep 29, 2009

### Jordash

1. The problem statement, all variables and given/known data

I have a couple of questions about one of my homework assignments any help would be greatly appreciated.

1. How do you find the Voltage drop of a Resistor in an AC Circuit is it similar to DC? V=IR The Resitor value is 68 ohms and there is an 80mH inductor in front of it.

2. Would it be V=Ipeak x R3 If I was trying to find the voltage drop for R3

3. When it asks for the impedance of R3 it means the Resistance of R3 right?

4. It also asks for the Impedance of an Inductor which I know is Zinductor=+jwL (where w is rad/sec frequency)

The equation for this problem is Vs(t)=10sin(400t) the Inductor L = 80 mH

so I calculated the impedance of the Inductor to be Zinductor=+j400 x 80mH which came out to Zinductor=+j32Ohms is that correctly done?

5. It also asks for the Voltage Drop across the Inductor so that means that the Voltage Drop would be calculated as if the Inductors Impedance were a Resistance right? So it would be done same as Above?

2. Relevant equations

3. The attempt at a solution

2. Sep 29, 2009

### rl.bhat

1) Yes. V = IR. But to find I you must find the total impedance of the circuit. In this case
Z = sqrt( XL^2 + R^2)
2) In Ac circuit V and I are usually RMS values.
To check the other show your calculations.

3. Sep 29, 2009

### Jordash

3. I'm just asking if impedance is equivalent to Resistance when it asks for the Impedance of a Resistor.

4. The equation given is Vs(t)=10sin(400t) and the Inductor L is 80mH so from those two values I came up with the following as the value of the Impedance of the Inductor.

Zinductor=+jwL=+j400x80mH=+j32Ohms or (32+i)ohms for engineering notation, is that correct?

4. Sep 29, 2009

### rl.bhat

3) We find the impedance of a circuit when it contains an inductance or capacitor or both along with a resistance. Impedance of the resistance is the resistance itself.
4) Your value is correct. But (32 + i) is not correct.

5. Sep 29, 2009

### Jordash

what is wrong with 32+i isn't that what the +j32Ohms represents? I thought j was used in electronics because i is used for current.

6. Sep 29, 2009

### rl.bhat

What do you mean by (32 + i) ? What is i stands for?

7. Sep 29, 2009

### Jordash

i is what you would actually put into a calculator i=sqrt(-1) or something like that.

8. Sep 29, 2009

### Jordash

i is what you would actually put into a calculator i=sqrt(-1) or something like that.