Zth is XL || with 60 ohms. I'm having difficulty finding XL because the inductor is shown in Henries. Frequency is not given. Can I substitute a frequency?

 

Can you ask your instructor what is the frequency?

 

Can you ask your instructor what is the frequency?

No ))) . There were two questions, multiple choice, about the circuit. One asked what the Eth was and the other asked what the Zth was. And that was it. It did imply that the circuit was to be used to plot the effect of frequency on the 50 ohm load. So I could graph it using different values of frequency. Seems a bit BS though. The writers of the lesson material ramble a lot, and it's difficult to find answers in the lesson. I can say I haven't used any of this crap since I learned it years ago. I'm a non-degreed Engineer that does System Testing. I don't design. I'm retired now and just trying to get a degree to say I did it.

 

How do you figure that Zth is something in parallel with 60 Ω?

In making that claim, you are claiming that the presence of that 20 Ω resistance significantly influences the circuit as seen by that load. Does that make sense to all of your years of experience as a non-degreed engineer?

You don't need a frequency to find Eth or Zth, they will simple be frequency dependent. Which makes it pretty easy to turn around and plot them as a function of frequency, doesn't it.

What was the form of the answers given in the multiple choice options? If they weren't parameterize in frequency, then the next thing to check is whether only one of the answers offered was possible at any frequency. What's the smallest that Zth can be? What's the largest? Same for Eth.

 

How do you figure that Zth is something in parallel with 60 Ω?

In making that claim, you are claiming that the presence of that 20 Ω resistance significantly influences the circuit as seen by that load. Does that make sense to all of your years of experience as a non-degreed engineer?

You don't need a frequency to find Eth or Zth, they will simple be frequency dependent. Which makes it pretty easy to turn around and plot them as a function of frequency, doesn't it.

What was the form of the answers given in the multiple choice options? If they weren't parameterize in frequency, then the next thing to check is whether only one of the answers offered was possible at any frequency. What's the smallest that Zth can be? What's the largest? Same for Eth.

 

You haven't said anything in post #5.

Were the multiple choice answers purely numerical? You could always show XL as XL = j ω L, and work the problem with that symbolic value. Doing that would show that you know how to work the problem.

 

Ohms for Zth and Volts for Eth. So you are saying: Ignore the 20 Ohms

You haven't said anything in post #5.

Were the multiple choice answers purely numerical? You could always show XL as XL = j ω L, and work the problem with that symbolic value. Doing that would show that you know how to work the problem.

Yes all scalars and I may use jwL
experience as a non-degreed engineer is at the systems level. I don't design. I troubleshoot systems to the next replaceable unit. I don't troubleshoot to the component level.

 

You ignore the 20 ohms because it's in parallel with a voltage source. The internal impedance of a voltage source is zero (a short, in other words). A short in parallel with 20 ohms is just zero ohms; the 20 ohms is of no effect because it's shorted out.

 

Or another way to rationalize why you can ignore the 20 Ω resistor is because, since it is connected directly across an ideal voltage source, the voltage across it is a fixed constant and, therefore, so is the current. No matter what happens elsewhere in the circuit, this isn't going to change and, because it isn't going to change, it can't have any influence on the rest of the circuit (unless there is some element, such as a current controlled source, that is dependent on the current in that resistor or perhaps the magnetic field near it or something similar, which is not the case here).

 

Ohms for Zth and Volts for Eth. So you are saying: Ignore the 20 Ohms

Yes all scalars and I may use jwL
experience as a non-degreed engineer is at the systems level. I don't design. I troubleshoot systems to the next replaceable unit. I don't troubleshoot to the component level.

What were the answer options for the questions?

Not trying to be critical here, but did want to make a point for your consideration. You were complaining how you never used this stuff in so many years of working as a non-degreed engineer and, consequently, seem to view all of this as useless crap. But you've also acknowledged that you've never done design work. But that's a BIG part of what engineers are expected to be able to do. So perhaps it isn't useless crap, but rather valuable skills and knowledge that you haven't needed to use up to this point because you haven't really been acting as a full-up engineer, degreed or not. Now is your opportunity to learn those skills that will enable you to do design.

I'm really just suggesting that you might try to step back from some preconceptions about what is and what is not useful to an engineer and focus on learning the concepts and gaining the skills that are part of your degree program. I think you will not only learn them much better if you do, but that you will also enjoy doing so much more.