Interview Questions—memorable times on both sides


As I travel this week for TI’s university recruiting I think back on some memorable interviews—ones on both sides of the table. One still haunts me. I was seeking my first industry job, one that I desperately wanted but was not offered. I’ve long wondered whether the way I handled a particular technical question made a difference. I’ll get to that question in a moment.

Through the years I’ve seen various articles on interview questions for engineers. Some are tricky puzzles, guaranteed to torment. Others are checks on basic skills. Working through the questions can be a good tune-up for the interviewer, too. A recent blog on EDN’s site had an interesting interview question for op amp devotees. Check it out.

I’ve had some spirited discussions on interviewing philosophy through the years. One of my most respected and highly technical colleagues insists that a successful candidate must be able to answer specific questions on the internal workings of op amps. I’ve used a similar approach in the past but I’ve turned a different direction. I now prefer to find an area that the candidate thinks s/he knows best, then judge the depth and maturity of that knowledge with some questioning. My assumption is that, given exposure to our products and technical issues, they would soon develop a similar depth of understanding. We develop interviewing approaches that suit our personal style and sense of what works.

I often ask a candidate whether they repair things—a car, bike, computer, motorcycle, sewing machine… whatever. Having the confidence to say, “I can figure this out” is something fundamental in a real engineer. Repairing things says that they practice being an engineer in everyday life. A good sign.

An exhilarating feeling comes when I am able to teach a candidate something s/he doesn’t know—something that’s a bit surprising and gives new insight. At the moment the light bulb comes on (if it does), there is a strong connection between us. To me it says, “This person gets it and can grow.” To the candidate it says, “I’m going to learn at this place!” I’ve had engineers replay that moment to me much later in their career. An old mentor called that feeling a “psychic paycheck”—(thanks, Denny).

Our university staffing organization is super-organized this year, rolling out an interviewing method that will unify our approach across the company. Seems to make sense and we’ll see how it works. Still the technical portion of the interview is left to us, the technical wonks. That leaves plenty of latitude to argue about the best approach and come up with our own questions.

Okay, I promised to tell you the interview question that has dogged me for 41+ years:  You have a 1V AC source driving a 1Ω resistor in series with a 1Ω reactance capacitor. What is the AC voltage across the capacitor?

No, not 0.5V. I didn’t fall for that trap. But, eager to show that I was not intimidated by some basic phasor math, I calculated the amplitude and phase of the capacitor’s voltage and explained the result. After some reflection, I thought I could have answered very quickly in a way that would have demonstrated recognition and understanding. Can you guess how I thought I should have answered?

I bet you’ve had interesting interviewing experiences, perhaps on both sides of the table. Maybe you’re willing to share your favorite interview question, experience or philosophy in comments below.

Thanks for reading.

Bruce        thesignal@list.ti.com

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  • Those of us that are audio geeks would recognize right off that V = .707VAC, since the -3dB point of a single pole RC filter is where the resistance and capacitive reactance are equal in magnitude.  You can answer the question by observation without recourse to any calculations at all.

    I remember interviewing at Tektronix just after college, and one of my interviewers asked me how to design a low-pass filter circuit with a -3d/octave slope rate.  Fortunately, I was familiar with converting white noise to pink noise, so i was able to give a sensible answer.  I've never forgotten that interview question,

  • Hi Bruce,

    Thanks for an interesting topic.

    I was responsible for hiring people in one company from the technical side until I stopped it. What happened? I realized that the result was 50/50. After a few years of thinking I found the reason. The passion and motivation are the main questions. I would tell you a story. Many years ago a young fellow came to an interview. He did not know anything!

    I offered him a very low position. I thought he would decline it, but he accepted it. After 10 years he was still young and he was a great engineer. I had never met before and after such a great and talented young engineer.

  • I would offer the position to the applicant who asked "Is this a typo?  Because capacitive reactance should be non-positive."

    For the record, if I had happened to remember that about capacitive reactance, I probably would have assumed that I was misremembering or had missed something.  At least back when I was interviewing.

  • Good question, but what is the phase shift? If you did not know the voltage, how could you tell when you where at .707Vac by phase shift?

  • A really interesting story. And I agree with Myron. The capability to understand is IMHO much more important than the capability to store knowledge. Any book can store knowledge but it won't make a good eingineer. And for any calculations, well, there's software for almost each problem - if you can properly model it.

    During my university times (which stretched long enough - as a student) I too often discovered that you only get the best ratings when you simple memorize what the professor has said. It was unimportant whether you really understood. Not knowing the right 'buzzwords' was putting you into the lower ranks. It was so frustrating that I often considered prematurely ending my studies. Luckily I'm not the type who easily gives up - I usually finish what I started.

    This continued when looking for a job. The jobs I got where those where my future employers already knew what I can do. And all have been very happy with what they got. But I never got a job when I was asked in the interview about what I know.

    However, often (not always) are people doing the interviews who by themselves do not know much about the operating field of the future employee. So they ask predefined quesitons and compare the answers. What else could they do?

    A typical failure was someone we hired for our next software version. We looked for someone who can program UI in JavaScript/Dojo. The 'winner' was indeed capable of doing the first steps for the new software. However, new versions of IE did require changes to the Dojo lib. And this guy was unable to figure out what to change where. The new situation was outside of his knowledge. At the end he left us and we lost the time we invested into the whole project. The prject was dumped and restarted using Flash. And the same thing happened again. When the existing knowledge wasn't enough, the project stalled. At the end, I was assigned to the software team and I had to learn Flex from scratch, expanding the range of my duties from hardware and firmware development to Flex client debugging and improvement. Everyone is happy now - except me :)

  • I have but one question for prospective engineers or technicians:  What is the base - emitter junction voltage of a transistor?

    Many engineers could not answer that question.  Only people who know working electronics know that answer.

    Larry Beaty

  • Larry: it depends on the transistor material (plain silicon?), temperature, base current and even collector/emitter voltage. The often cited 0.7V are only true in few situations.