Phase Difference between Voltage and Current

[Sylvia]

Homework Statement

The circuit above has a 29

resistor and a 11.1 mH inductor. Calculate the theoretical phase difference between the current CPA and voltage VPB if the circuit is driven by a sinusoidal voltage source with a peak amplitude of 3.5 V at the following frequencies:

20 Hz
420 Hz

Homework Equations

tan(x) = (XL / R), XL = (omega)(L)

3. The Attempt at a Solution

I tried substituting into the given relevant equations, and for 20 Hz, I got 2.75 degrees. However, this is the wrong answer. Please help!

 

[gneill]

Your relevant equation would give you the phase angle of the overall impedance, and that would in turn tell you the phase angle of the current with respect to the source voltage. But the question is asking you to compare the current's phase to that of the voltage across the inductor. You'll need to find expressions for the current and for VP_B.

 

[Sylvia]

So current = 3.5 V divided by Ztotal, and VPb = I * L * omega?

 

[gneill]

So current = 3.5 V divided by Ztotal, and VPb = I * L * omega?

That's the idea. Don't forget the "j" in the inductor's impedance.

 

[Sylvia]

Im confused about where to proceed from there (my professor has done a horrible job of teaching this subject and the textbook isn't making much sense to me unfortunately)

 

[gneill]

Im confused about where to proceed from there (my professor has done a horrible job of teaching this subject and the textbook isn't making much sense to me unfortunately)

Calculate the current and the voltage VP_B. Put the results in polar form (magnitude and phase angle).

 

[Sylvia]

Uhhhh sorry I'm in the non-calculus based class...

 

[gneill]

Uhhhh sorry I'm in the non-calculus based class...

? No calculus involved. Just circuit rules like Ohm's law.

 

[NascentOxygen]

Calculate the theoretical phase difference between the current CPA and voltage VPB

When you look at this closely, you can see that the question being asked is quite basic: what is the phase difference between current through an ideal inductor and the voltage across that ideal inductor.

No calculations are needed!

BTW, anyone know what is supposed to be represented by that box with a + and - on it??

 

[Mudpie]

BTW, anyone know what is supposed to be represented by that box with a + and - on it??

Ammeter?