I don't think the interviewer wants math equations. He wants to see 3 output lines of that cap charging. This will show him if you understand circuit configurations. The character of those 3 lines will tell him.

Good points. This is making me confused. Can you explain it to me? But how I show the curve to him. Like below.


I am not sure how capacitors work correctly. Please help me.

 

You need to know about current being faster than voltage, voltage being faster than current. What is a coil and what is a capacitor.

In capacitor, voltage faster than current; for inductor, current faster than voltage. Please explain it to me.

 

First of all is it off-phase with 180 degrees or 90?

Is it DC or AC?

The capacitor has infinite resistance by DC current and 0 resistance by AC current, so the voltage is first with a DC circuit. The DC current is blocked.

The coil has infinite resistance by AC current and the current is first, it has 0 resistance by DC current, meaning it blocks the AC current and let's through the DC, so the current is first.

 

I am not sure how capacitors work correctly. Please help me.

Quit wasting your time looking for jobs in electronics, unless and until you have a solid grasp of these basic principles. There are plenty of students in line in front of you that DO have that basic knowledge. I'm not trying to discourage you, only to suggest that your timing is off.

 

Quit wasting your time looking for jobs in electronics, unless and until you have a solid grasp of these basic principles. There are plenty of students in line in front of you that DO have that basic knowledge. I'm not trying to discourage you, only to suggest that your timing is off.

That is the purpose I come to the forum. I try to get the basic even i can solve those math problem.

 

I have done same kinda project last month.

can I read your it?

 

First of all is it off-phase with 180 degrees or 90?

Is it DC or AC?

The capacitor has infinite resistance by DC current and 0 resistance by AC current, so the voltage is first with a DC circuit. The DC current is blocked.

The coil has infinite resistance by AC current and the current is first, it has 0 resistance by DC current, meaning it blocks the AC current and let's through the DC, so the current is first.

Thank you for your explaination.
Input is step function. Here are there circuits. Find out it output.


if you traced back, I have solved the two order differential equation for C and L circuits. I know high frequency signal can go through capacitor, dc can't. High frequency current can't go through an inductor. I just want to know what real happens when charger capacitor and inductor. I don't want to just mathmatically solved the problem, I want to know the detail in phyiscs.
Based on v = L di/dt and i = C dv/dt, we know that current and voltage are 90 degree shift.
In this way, I can anwer this interview questions.

 

You might know the math equations.......but if you had a bread board and a scope.....you might be quite surprised. When some people see the waveform of problem #2......they wonder how this could be.

Your prospective employer is a smart man.

Turn circuit #2 on and watch peak voltage across cap. When you see the waveform.....you will be distracted....but check out the peak. Compare it to the peak voltage on circuit #1.

Once you understand #2......and review circuit Q......you'll figure out #3.

 

You might know the math equations.......but if you had a bread board and a scope.....you might be quite surprised. When some people see the waveform of problem #2......they wonder how this could be.

Your prospective employer is a smart man.

Turn circuit #2 on and watch peak voltage across cap. When you see the waveform.....you will be distracted....but check out the peak. Compare it to the peak voltage on circuit #1.

Once you understand #2......and review circuit Q......you'll figure out #3.

I do not believe his prospective employer is a smart man.

Most likely they will ask him to draw the current and voltage wave forms for all circuits, ask him why its so and then ask him to write the formulas.

 

I ask these types of questions when I interview new grads or interns. I am not looking for right answers. I usually just ask these questions to see what the reaction is. If they start sweating like they just saw a ghost, it raises a red flag. I ask this to see what the problem solving skills are like. So, if you nail this question in under 30 seconds, that is great. Unfortunately, that means I have time for even tougher questions.

 

Thank you for your explaination.
Input is step function. Here are there circuits. Find out it output.
View attachment 153017

if you traced back, I have solved the two order differential equation for C and L circuits. I know high frequency signal can go through capacitor, dc can't. High frequency current can't go through an inductor. I just want to know what real happens when charger capacitor and inductor. I don't want to just mathmatically solved the problem, I want to know the detail in phyiscs.
Based on v = L di/dt and i = C dv/dt, we know that current and voltage are 90 degree shift.
In this way, I can anwer this interview questions.

Hello there,

From your previous posts i can see that you are not ready for questions like this, or should i say circuits like this. I hate to say it but this is really really basic stuff, so if you dont know how to figure out what the waveshapes should be before you actually analyze them, then you must analyze them and then you can start to make general statements about how they work. The key here though is you must analyze them at least once or you'll never know how they work. It also takes a little in depth analysis and overview to realize that they each have certain important features that are not shared between the three.
For example circuit #2 creates a sine wave oscillator simply because there are no losses, and because the inductor is on top there will be a DC offset as well. The most important point though is that it has no losses so the circuit will oscillate. This is different than circuit #3 which has a resistor which causes some losses, and there are three distinctly different types of responses for that circuit.
To understand those kinds of concepts you have to analyze the circuits and perhaps read about them on the web.
You can of course ask here as you did and if this is not homework we can give you answers and ways to analyze these as well as almost any other circuit you will encounter.

It takes time to get the kind of overall understanding of circuits like this but it all starts with analysis and probably most important a good book that goes though these kinds of circuits in detail. The most important theoretical concepts are often not apparent so you have to read up on how they work, or people here can help you.

I would start by reading up on them, but also with nodal analysis and see what happens when you vary the different components. For the last circuit though you probably have to be taught the different types of responses that are possible as sometimes it is very difficult to pull out the most important aspects of a circuit without being actually told outright.

Once you learn general circuit analysis you will find that you have to ask less and less questions, although like i said sometimes you have to be told or read about it in a good book.

 

I hate to say it but this is really really basic stuff...

I’m glad you did say it. He needs to hear it from more than one of us. I remember seeing those basic circuits in both physics and diffy Q, and I wasn’t a major in either of those. In the lattter they were given as more or less simple applications and we spent very little time on them. After all, they have solutions, unlike most of diffy Q.

 

Hello there,

From your previous posts i can see that you are not ready for questions like this, or should i say circuits like this. I hate to say it but this is really really basic stuff, so if you dont know how to figure out what the waveshapes should be before you actually analyze them, then you must analyze them and then you can start to make general statements about how they work. The key here though is you must analyze them at least once or you'll never know how they work. It also takes a little in depth analysis and overview to realize that they each have certain important features that are not shared between the three.
For example circuit #2 creates a sine wave oscillator simply because there are no losses, and because the inductor is on top there will be a DC offset as well. The most important point though is that it has no losses so the circuit will oscillate. This is different than circuit #3 which has a resistor which causes some losses, and there are three distinctly different types of responses for that circuit.
To understand those kinds of concepts you have to analyze the circuits and perhaps read about them on the web.
You can of course ask here as you did and if this is not homework we can give you answers and ways to analyze these as well as almost any other circuit you will encounter.

It takes time to get the kind of overall understanding of circuits like this but it all starts with analysis and probably most important a good book that goes though these kinds of circuits in detail. The most important theoretical concepts are often not apparent so you have to read up on how they work, or people here can help you.

I would start by reading up on them, but also with nodal analysis and see what happens when you vary the different components. For the last circuit though you probably have to be taught the different types of responses that are possible as sometimes it is very difficult to pull out the most important aspects of a circuit without being actually told outright.

Once you learn general circuit analysis you will find that you have to ask less and less questions, although like i said sometimes you have to be told or read about it in a good book.

Thank you for your help. This is not homework, just interview questions. I ansnwered them and told them about the first circut expenenial wave, which is charge circuit, the second one is oscillator circuit and the third one is die out circuit. But i don't get offer. That is why I came here to ask questions. Can you tell me what circuit books I can read?
Thanks

 

Before you embark on a degree program for Electrical Engineering, which may be what the interviewer was looking for, you should invest some effort in learning what a career in that field is like, and whether that or some other field is a good match for you. You have a big investment to make, in money and time, to get the right education for the career of your choice. Choose wisely.

 

Thank you for your help. This is not homework, just interview questions. I ansnwered them and told them about the first circut expenenial wave, which is charge circuit, the second one is oscillator circuit and the third one is die out circuit. But i don't get offer. That is why I came here to ask questions. Can you tell me what circuit books I can read?
Thanks

Hello again,

Well it kind of depends on what math you have had in the past, but if you have had Calculus then a good one is Engineering Circuit Analysis by William H. Hayt, but i am sure there are others.
If you did not have calculus yet, you might still gain insight from that kind of book but calculus is really good for this subject area.
That book may be expensive for a recent edition, but you might find an older edition that would be cheaper or even a used version. The newer versions will probably come with a CD disk too though with various helps on it.

I am sure there are other books too that are similar. At Amazon you can often find book listings that allow you to look inside the book, and so you can look at the table of contents to see if it holds what you are looking for.

The material is usually about a general analysis method or methods, and also about RC circuits, RL circuits, and RLC circuits and that's where you get the important ideas from for these kinds of circuits.
Once you get a general analysis method down you can also do you own experiments by looking at the simple circuits and trying to think about what happens when you change element values.
Also, dont be afraid to use a simulator like the free LT Spice simulator. You can connect components and start getting interesting results right away. It's very very well worth learning that software. Just dont let it be the only way you analyze circuits

 

Good points. This is making me confused. Can you explain it to me? But how I show the curve to him. Like below.
View attachment 152946

I am not sure how capacitors work correctly. Please help me.

If this were what you were to draw for me and I were interviewing you, I would wish you luck and move on to the next candidate.

While there is quite a bit of flexibility in what might be reasonable answers, I would generally be looking for an awareness of certain concepts such as time constants, first and second order response, under damped, critically damped, and over damped responses. I'd also hope to see an awareness of transient verses steady state response. On a plot I would expect to see labeled axes with a reasonable indication of scale relative to the parameters in the problem.