Simple interview question

Discussion in 'General Electronics Chat' started by WBahn, Jun 20, 2012.

  1. WBahn

    Thread Starter Moderator

    Mar 31, 2012
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    Not necessarily. I don't hold wrong answers against someone right away. Anyone can look at a circuit and see something that isn't there or make an invalid assumption that should have been obviously seen as incorrect. That's why I ask followup questions.

    And, after telling me this, I would ask you to explain what it means for a transistor to be in saturation and then whether or not the circuits were consistent with being there. I'd see how well you handled that and how much effort it took to get you to the conclusion that (a) definitely is not in saturation and, depending on the path you set out on, we would talk about the implications of assuming that (2) was in saturation.

    Keep in mind that it is an interactive interview, so I don't ask the next question until we have dealt the previous one (not necessarily to the point of having a correct answer, but at least to the point where I had a good feel how the person arrived at the answer they got). This would almost certainly change your answers to some of the rest of the questions. But if you say something like, "When Vin is 0V I expect the output in circuit (a) to be -10V, I would ask what the Vbe is and, upon saying that it was 0V, I would what mode of operation that placed the transistor in and, if you said cut-off, I would then ask about whether that was consistent with the transistor being in saturation.

    One thing I'm really looking for is self-consistency and the ability to recognize when things are not self-consistent. For instance, for circuit (a) you said that you expected Vout and the emitter voltage to both be -10V. Since these are the same node, those answers are self-consistent. But you also indicated that the base emitter voltage would be 0V. So I would ask how you arrived at that and, if necessary, ask explicitly what the base voltage was, what the emitter voltage was, and what the base-emitter voltage then was. If you just made a mental math error, I want to discover that, let you correct it, and move on.

    If I remember correctly, you are just starting an EE program (or am I thinking of someone else?). These are things that you might first see anywhere from a Circuits I course (a brief introduction near the end, probably) to an Electronics I course (very in depth). If you haven't gotten this far, then don't worry. If you have gotten this far, then worry -- and then go back and fill in the gaps.
     
  2. WBahn

    Thread Starter Moderator

    Mar 31, 2012
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    Yep. I also forget to point out that most engineers also needed to do the lab testing on the chips that came back from fab.

    This experience was before I first saw the MIT video, so the video didn't shock me as much as it would have a few years earlier, though I was dismayed that it was MIT.

    We do need to keep in mind that I only did the physical breadboard thing in one round of interviews (actually, one day of interviews), so the sample size is very small. It was also well over a decade ago. I think we interviewed four or five people that day. So words like "most" become a bit stronger sounding than they deserve. I know only one person wired it up with no problems - and proceeded to immediately let the magic smoke out of the transistor, from which they concluded that they must have done something wrong. Everyone else (i.e., one or two people) struggled with it and I had to point out mistakes before they got it right.

    I definitely agree, at least taken together with a bunch of other things. Engineering schools, as a rule, simply don't want to teach hands-on practical electronics. On the flip side, many students don't want to be bothered with it, either. I had one student say flat out, "Why should I have to waste my time in a lab course? When I'm engineer I'll have technicians to do this stuff for me."

    I don't know the best way to classify it. I don't think it is a trick question in the sense of relying on some obscure, subtle, hard to see element. I think it is a completely fair came question. The impetus for the question was that I was getting tired of candidates regurgitating memorized formulas and throwing them at problems. If they regurgitated the right formula, I had no idea if it was because they knew which formula was applicable or if they just got lucky. So I wanted a question that required them to think outside their Box of Formulas.
     
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
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    My college classes start in the fall. I'll be starting with basics for one year at the community college, and then next fall (2013) I'll actually get into some electronics courses at the university. Right now I'm only in summer school remedial algebra so I can be ready for regular college algebra in the fall. So, long ways away. I wouldn't even be applying for this job, but I've been hearing you talk about this interview question and couldn't resst the urge to take a shot at it.
     
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