How to find the values of L and VL

WBahn

Joined Mar 31, 2012
29,976
Do you really think that that is enough information for anyone to have even a hint of clue what you are talking about?

What is L? An inductance?

What is LR? The product of L and R?

What kind of circuit? A series combination of an L and an R? A parallel combination? Something else entirely?

Don't make people have to guess even the most basic things about your problem. We are not mind readers!

You also need to show YOUR work to at least attempt to solve YOUR homework problem.
 

drc_567

Joined Dec 29, 2008
1,156
L/R is a time constant ... 5 of which constitute the time interval at which a step function input will reach steady state ...
...any help?
 

Thread Starter

Riccardo Ribaudo

Joined Dec 5, 2016
6
I do apologies ,
I didn't mean LR , I meant VL

The question I've been given is to find
The voltage across the inductor, VL
Reactance, XL
Inductance, L
Impedance, Z

These are the values I've been given
F=5kHz
I=5mA
R=5.2kohms
VR = 26v

Hope this helps somewhat more ?




Do you really think that that is enough information for anyone to have even a hint of clue what you are talking about?

What is L? An inductance?

What is LR? The product of L and R?

What kind of circuit? A series combination of an L and an R? A parallel combination? Something else entirely?

Don't make people have to guess even the most basic things about your problem. We are not mind readers!

You also need to show YOUR work to at least attempt to solve YOUR homework problem.
 

WBahn

Joined Mar 31, 2012
29,976
I do apologies ,
I didn't mean LR , I meant VL

The question I've been given is to find
The voltage across the inductor, VL
Reactance, XL
Inductance, L
Impedance, Z

These are the values I've been given
F=5kHz
I=5mA
R=5.2kohms
VR = 26v

Hope this helps somewhat more ?
Not really.

Consider this: I have a circuit with two resistors, one is 2 kΩ and the other is 5 kΩ. The current in the 2 kΩ resistor is 10 mA. What is the current in the other resistor?

Before you can answer this question, wouldn't it be nice if I showed you the circuit?

Why won't you show us the circuit?
 

Thread Starter

Riccardo Ribaudo

Joined Dec 5, 2016
6
Not really.

Consider this: I have a circuit with two resistors, one is 2 kΩ and the other is 5 kΩ. The current in the 2 kΩ resistor is 10 mA. What is the current in the other resistor?

Before you can answer this question, wouldn't it be nice if I showed you the circuit?

Why won't you show us the circuit?
 

Attachments

WBahn

Joined Mar 31, 2012
29,976
Well, that's progress.

Is the frequency 5 kHz (your original post) or 7 kHz (the drawing)?

Still need that whole "show YOUR work" thing....
 

Thread Starter

Riccardo Ribaudo

Joined Dec 5, 2016
6
Yes the frequency is 7kHz

That is all I've been given that circuit with these questions that are written on paper that I posted earlier
The question I've been given is to find
The voltage across the inductor, VL
Reactance, XL
Inductance, L
Impedance, Z
 

WBahn

Joined Mar 31, 2012
29,976
So the next step is, yet once again, SHOW YOUR WORK!!!!!

Do NOT expect people here to just work your homework for you and give it to you on a silver platter.

SHOW YOUR WORK!!!!
 

MrAl

Joined Jun 17, 2014
11,389
I have a circuit with
F=5kHz
I=5mA
R=5.2kohms
VR = 26v
L=?
LR=?
How do i find the values of L and LR?
Hi,

I guess this is a series circuit with one R and one L and an AC source voltage of 26vac rms and resistance is 5.2k and I is 5ma ac rms and frequency is 5kHz. I am guessing though since you did not show the circuit.

In the homework section we ask that the poster shows some of his first attempt to solve the problem, unless of course they have no idea whatsoever on how to go about solving this.

It looks like you need to find the value of L first. This kind of problem is often called a 'synthesis' problem because the question would come up when trying to design a network where you know how ti should behave and you know the topology but you dont yet know the right values in order to get it to meet the specs. To handle this kind of problem you usually just reverse what you know about how to analyze a circuit, but once you get the equation(s) needed you just solve them for one or more of the circuit elements rather than one of the values of current or voltage. So you can analyze the circuit ly for a voltage or current or both representing L symbolically, then solve the equation(s) for L instead, then plug in the values and you should get a numerical value for L. Then you can go from there.

You should really post the circuit and tell us exactly what you do not understand.
 

RBR1317

Joined Nov 13, 2010
713
One should look at the description of this problem in terms of a phasor diagram. Note that the same current flows through each component, so the current will make a good zero degree reference. The resistor voltage must be in-phase with the current so the resistor voltage is also at zero degrees. Now the voltage across the inductor must lead the current by 90 degrees, and lead the resistor voltage by 90 degrees. First step of the solution is to find the voltage across the inductor.
Phasor_B.xpm.png
 

WBahn

Joined Mar 31, 2012
29,976
One of the reasons that we need to see YOUR attempt at a solution is that it gives us some insight into two things: (1) The basic method that you have been shown how to approach problems such as this -- for instance, do you use phasors, do you use complex analysis, do you use reactances, etc., and (2) where are you going right and where are you going wrong.

When you steadfastly refuse to show even an attempt to work the problem, it not only makes it much harder to give effective help, but it goes a long way to confirming the suspicion that you don't even want help to begin with, but rather you just want someone to do your homework for you.
 
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