Help explaining some practice test questions

Discussion in 'Homework Help' started by lokeycmos, Jun 9, 2013.

  1. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
    432
    7
    im studying for an electronics certification exam and I had a few problems I need help explaining. I have attached 4 screenshots of the questions I need an explanation for and how to slove them.hopefully explained in a way that's easy to remember. the questions are #46, #53,#73, and #90. the correct answers respectively are B,A,D, and D.
     
    • 46.jpg
      46.jpg
      File size:
      168.7 KB
      Views:
      38
    • 53.jpg
      53.jpg
      File size:
      160.4 KB
      Views:
      28
    • 73.jpg
      73.jpg
      File size:
      198.2 KB
      Views:
      24
  2. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
    432
    7
    Heres the fourth screenshot
     
    • 90.jpg
      90.jpg
      File size:
      243.1 KB
      Views:
      28
  3. WBahn

    Moderator

    Mar 31, 2012
    17,766
    4,801
    On #46, none of the answers are possible since, for instance, +3 is not a voltage, it is just a number. The people that wrote the exam clearly meant +3V, but that doesn't change the fact that they are clearly not qualified to pass any type of electronics certification exam, let alone write one. But the field is rife with such types so you just have to deal with it.

    Interpreting each number in the answers as a voltage, in volts, B is the only one that would have the transistor in the active region in the normal configuration. The conditions in A and C will put it in the active region, but where the collector and emitter are swapped. Swapping C and E leave you will an NPN transistor, just one with really poor characteristics.

    Answer B has a Vbe of 2V, which is definitely forward biased (excessively so). It's arguable whether this qualifies as "proper" bias, but this is the only answer that has the base-emitter forward biased at all.

    In #53, the exam writer's once again show that they live in an ivory tower and not the real world if they are going to give resistor values to four and five sig figs and expect them to stay that accurate when they have 75W being dissipated in them. But, again, you just have to deal with it.

    This is a very straightforward problem. You need to show your attempt to solve it and we will be happy to look and see where you are going wrong. The answer they give is the correct one (well, it should really be 75.76 ohms).

    For #73, we have to assume they are not really talking about a 'class 'C' collector', but rather meant to say, "In a class 'C' amplifier, the collector".

    What do you know about the conduction periods for class A, B, and C amplifiers?

    Again, the given answer is the best of those given.

    For #90, what is the "modulus" of a counter? How many states does a 5-bit binary counter have?


    You really need to show your attempts at any problem you post on AAC. We will not just provide solutions for you.

    Also, the fact you are specifically looking for things that you can memorize easily so solve these particular problems is a bit concerning. I want a human being that understands the concepts well enough to solve the problem, not a monkey that has memorized how to parrot one.
     
    screen1988 likes this.
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    I would prefer Q#46 D as the answer. It could possibly represent proper bias for class 'C' operation, with the transistor biased beyond cut-off. I find answer B less convincing (or not at all convincing) for the reason already given by WBahn.
     
  5. WBahn

    Moderator

    Mar 31, 2012
    17,766
    4,801
    Good point. Given the quality of the questions and answers, I doubt that the writer would be capable of being that subtle, though. Apparently they weren't, either, since they assert that B is the "right" answer. I hope the bulk of the exam isn't this poorly written.
     
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    The test shown is the ETA's Associate Test.

    I noticed question 50 asking for the current acrossed a specific resistor.

    You can redress your concerns by contacting the ETA via their website. I plan to review the whole test before commenting to the ETA.

    Attached is the full test ...
     
Loading...