Calculate frequency from Voltage and Phase shift

Thread Starter

G_Raas

Joined Feb 12, 2017
20
Hi all,

Is there a way to calculate frequency if given (and only given) the polar voltage drops of Vr, Vl, Vc and the Inductance and Resistance? We are given the aforementioned values and asked to solve for the source voltage, frequency, current and impedance... Is this doable or did our prof. Maybe forget to add some values (typo)?

Our prof. Is coming back from a 2 month vacation and giving us a test (we are on reading week break currently) in 4 days... I have already tried emailing/contacting him but he has not responded (2 days wait so far) and I really want to move past this one question as soon as possible.

So, is it possible to calculate frequency using only VR, VL, VC and each corresponding Phase shift and Resistance and Inductance, nothing else is given?

Thanks in advance!
 

Thread Starter

G_Raas

Joined Feb 12, 2017
20
Please let me know if specifics are needed? I would love to be able to show my work, but as far as I can tell I need the frequency in order to calculate my XL and XC values in order to get my total impedance in order to calculate my current.
Without being able to calculate the frequency, I dont see how I can even start calculating any other values.

Am I missing something really obvious? I thought I knew this subject fairly well (although it was never covered in in-class lectures), but it appears as of now that I missed something somewhere... I am not looking for anything much more than just a sanity check really... :) Tell me it is possible and I will return to my studies and redouble my google-fu efforts at finding out how to solve this.

Many thanks in advance!
 

WBahn

Joined Mar 31, 2012
26,398
Doesn't it seem likely that how these three components are connected might come into play?

If I hook up all three in series, or all three in parallel, or one in series with the parallel combination of the other two, or one in parallel with the series combination of the other two, that that might influence the measurements.

You might be able to tease out the topology by determining the constraints that each of the possible combinations places on the voltage and phase relationships.
 

Thread Starter

G_Raas

Joined Feb 12, 2017
20
Doesn't it seem likely that how these three components are connected might come into play?

If I hook up all three in series, or all three in parallel, or one in series with the parallel combination of the other two, or one in parallel with the series combination of the other two, that that might influence the measurements.

You might be able to tease out the topology by determining the constraints that each of the possible combinations places on the voltage and phase relationships.
Thank you for your response. It is a simple series circuit... This a year 1 (2nd semester) college class, so if there is a solution, I wouldnt expect it to be a very complicated process otherwise I am hopeful that the prof would have made sure to cover it off in an in-class lecture...
 

WBahn

Joined Mar 31, 2012
26,398
Thank you for your response. It is a simple series circuit... This a year 1 (2nd semester) college class, so if there is a solution, I wouldnt expect it to be a very complicated process otherwise I am hopeful that the prof would have made sure to cover it off in an in-class lecture...
Consider the following:

If I tell you the current through a known inductance and the voltage across it, can you determine the frequency?

What do you know about the current components in series?

If you know the voltage across a known resistance, can you determine the current through it?
 

WBahn

Joined Mar 31, 2012
26,398
Here is the pre-test work-sheet being referenced (attached). The problem set in question is the 6th row down. Again, thanks for your help all!
Go for the low hanging fruit and look at each empty box and see if you know enough information to fill it in. Once you have done that, do it again since you have additional information to work with. Keep doing this until you can't fill any more boxes.

Then look at each unfilled box and ask exactly what missing information is needed to fill in that box. Then look at each piece of needed missing information and see if there is any way to get it based on what you do have.

As you do this, keep in mind that there are often more than one way to get a given piece of information, so consider as many different possible routes as you can think of.
 

BR-549

Joined Sep 22, 2013
4,938
It's too bad you waited so long, before asking this question. It's a great question and you should spend time with it. The only quick "rule of thumb" I can advise you of........try to find something common in the circuit.

I feel terrible when I pass a class.......and don't know what they're talkin about. I feel cheated. Did they cheat me....or did I cheat me?

This subject matter/career....is competitive and complicated. You have to want to know it. Sliding by won't feel good.

Good Study......Luck doesn't work.
 

Thread Starter

G_Raas

Joined Feb 12, 2017
20
Thank you all.

I am getting the sense I am overlooking something... I will pinder your suggestions over my coffee this morning. I think I am starting to see a light bulb finally!

Thanks so much!
 

Thread Starter

G_Raas

Joined Feb 12, 2017
20
Got it figured out now... Thanks for your guidance all. I really appreciate it.

The problem preventing solving this one was just lack of awareness that XL = VL÷IT... This wasnt something that was ever called out specifically to be aware of in class... Makes total sense in retrospect and should have been able to figure it out for myself but was just so focused on XL = 2×pi×f×L that couldn't see the other ways to calculate it.

Anyways, thanks again folks - you guys are great!
 
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