time for a laugh at the exam question - Page 1
Forum section: electronics / beginners

author: Simon
author_rank: Unknown
timestamp: October 20, 2021, 06:50:36 pm
content: d. A PV array needs to be fed into the grid. If 12 panels are to be used, using thespecification in Fig 2, draw and label the array arrangement to get 4 kW andspecify the voltage of the arraye. . Describe the power converter needed, include values where possiblef. What is the duty cycle for this converter? (DC/DC power converters were explained in the "notes")The panels shown are 300W, 305W and 310W of 32.4V.

author: TimFox
author_rank: Super Contributor
timestamp: October 20, 2021, 07:35:49 pm
content: It's a trick question to see if the student is confident enough to answer that the question, as posed, does not admit to a solution.Of course, insecure teachers hate to get that answer.

author: Simon
author_rank: Unknown
timestamp: October 20, 2021, 08:15:56 pm
content: no it's not a trick question, the tutor is that incompetent, as they say, those who can't - teach!

author: Simon
author_rank: Unknown
timestamp: October 20, 2021, 08:17:31 pm
content: I was failed at the question for not doing the diagram.... having explained it was a non question.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 20, 2021, 08:23:09 pm
content: It is not so difficult, just us an of the shelf converter with 110% efficiency.

author: Simon
author_rank: Unknown
timestamp: October 20, 2021, 08:50:59 pm
content: Quote from: Kleinstein on October 20, 2021, 08:23:09 pmOf course, given the absurdity of the question, the most logical response. unfortunately the tutors do not have a sense of humor....

author: Simon
author_rank: Unknown
timestamp: October 21, 2021, 07:27:10 am
content: I explained why a duty cycle could not be given, gave one anyway based on assumptions I warned were wrong. You see apparently a grid tie inverter is simply a DC/DC converter followed by a H-Bridge.....

author: Manul
author_rank: Super Contributor
timestamp: October 21, 2021, 10:59:12 am
content: Any lack of power can be fixed by simply adding letters PMPO. From that solar array 10kW - easy.

author: Simon
author_rank: Unknown
timestamp: October 21, 2021, 12:24:12 pm
content: Makes engineering sense.

author: BradC
author_rank: Super Contributor
timestamp: October 21, 2021, 12:30:12 pm
content: Quote from: Simon on October 21, 2021, 07:27:10 amYou'd better message that to treez, it'll save him months of questions.

author: CJay
author_rank: Super Contributor
timestamp: October 21, 2021, 12:40:13 pm
content: Quote from: BradC on October 21, 2021, 12:30:12 pm"Do you agree?"

author: CaptDon
author_rank: Super Contributor
timestamp: January 08, 2024, 03:39:32 am
content: I saw a simple but stupid question on a 'pre-hire' exam. "How high is a stack of washers if each washer is 5/16 inch thick" The obvious answer is 5/16" times X where X represents the number of washers in the stack. I was told that I was one of the few people who ever answered it correctly. Most just skipped it!!! You want an explaination of why there are so any train crashes on Norfolk Southern? One of the many exams you get during the 'gatekeeper' hiring process has far more questions than can be answered in the alotted time. They don't care how many you get wrong!!!! Only how many you get right!!!! The secret to the test is if you don't know the answer immediately skip it and go on. Answer as many as you can as fast as you can then go back and guess the rest!!!! Really!!! So, interpolating, if you don't know what the signal aspect means just run it and hit the next train head on as you'll probably get it right next time. These folks were the biggest bone heads I ever interviewed with, Well, except for maybe AirBorn in Lake City Pennsylvania. One of their interviewers was such an asshole I walked out of the interview but I did thank the interviewers who were serious and knowledgeable. It is a shame how one asswipe in management can make a work environment into a hell hole and kill employees spirits so they never rise to their real potential as a valued employee who contributes!! (P.S., Never tell Norfolk you worked for a short line railroad, that is an almost immediate "Skip this guy"!!! I know!!)

author: EEVblog
author_rank: Unknown
timestamp: January 08, 2024, 11:09:13 am
content: Quote from: Simon on October 20, 2021, 08:17:31 pmReminds me of when I failed a digital exam once because I used the IEEE logic symbols and the lecturer had no idea what they were and said I was wrong and just drawing jibberish.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 08, 2024, 02:45:00 pm
content: I'm sorry. I just don't get it.Can't you just move the Sun closer???

author: BradC
author_rank: Super Contributor
timestamp: January 08, 2024, 03:09:58 pm
content: Quote from: Wallace Gasiewicz on January 08, 2024, 02:45:00 pmSure, if you want to do it the easy way....

author: Simon
author_rank: Unknown
timestamp: January 08, 2024, 03:11:12 pm
content: Quote from: EEVblog on January 08, 2024, 11:09:13 amWhen I lived in Italy and went to school I got a question "wrong" because although answered in the perfect English of a native speaker the question was out of date and my correct answer was wrong. The electronics teacher did comment that the English teacher was a bit of a pain with this as she would ask him for help when in fact teaching electronics was not her job, it was to teach English.

author: Whales
author_rank: Super Contributor
timestamp: January 08, 2024, 03:37:18 pm
content: 300Wrms or 300Wp-p?

author: Simon
author_rank: Unknown
timestamp: January 08, 2024, 03:40:56 pm
content: No, if I remember correctly it was about the security of mobile phones versus landline phones, that anyone with a scanner could listen into mobile communication. By the time I was at school all mobile telephone comms were encrypted and more secure than the wired phone. Considering you would have "phone engineers" making calls on peoples lines from the box in the street and for this reason my grandparents had a device that monitored the line for use. So based on my English teachers outdated material I got 9 out of 10 right.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 09, 2024, 02:29:55 pm
content: Kinda in the same vein....In 1970 in our University Physics lab we had the acceleration ( gravity) experiment, lots of data points on a falling ball, as I rememberSo I decided to learn Fortran and computerize the results, including the graphs. Two sets of punch cards, one set for the program the other set for the data.We handed in the results on the big computer paper and received only a 9 out of 10 because we had not done our own work.HA!!

author: BillyO
author_rank: Super Contributor
timestamp: January 09, 2024, 04:18:33 pm
content: Just in interest's sake, what did the tutor tell you was the correct answer?

author: Siwastaja
author_rank: Super Contributor
timestamp: January 09, 2024, 05:13:59 pm
content: Note that you don't need magical over-100% efficiency to get 4kW out of 12*310Wp panels. This is just a nominal rating (specified in some conditions e.g. 1000W/m^2 irradiance at 25degC temperature or something); this is what you get in "usual" sunny conditions, with clean panels, aligned in an optimum way. All you need to exceed this power is extraordinarily good insolation. One condition where real PV panels significantly exceed their nominal ratings is overcast day which maximized stray light, plus a hole in clouds from where the panels get full unobstructed direct light.

author: Simon
author_rank: Unknown
timestamp: January 09, 2024, 09:45:13 pm
content: you expect someone that thinks my home can be heated in 45s with a 35kW boiler to understand all that about the clouds and solar panels?

author: Siwastaja
author_rank: Super Contributor
timestamp: January 10, 2024, 05:15:25 pm
content: Quote from: Simon on January 09, 2024, 09:45:13 pmIt is your job to completely and utterly overwhelm their poor mind with accurate information and correct calculations and then demand full score, and, if necessary, escalate the case to the higher-ups.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 10, 2024, 05:24:43 pm
content: Quote from: Simon on October 20, 2021, 08:17:31 pmI would've drawn 13 panels @ 310W.If my answer was marked incorrect, at least I'd have some substance to debate.It's impossible to debate/discuss a "non question" response.

author: Simon
author_rank: Unknown
timestamp: January 10, 2024, 07:16:26 pm
content: As I said these people have been the epitome of "those who can't, teach", they are so incapable that that they can't argue with you so will just stick to their guns. Happily my course is now over, I have submitted my project. Granted it went on for about 9 months, but I had 3 different tutors and frankly I'm pretty sure that the one who marked it was a forth.They have resorted to using Indian tutors but then as a distance course I suspect that most of the students are based in India anyway.The maths tutor's english was so bad that they had to get a task force of tutors to sort her material out, it read all over as non native english speaking writing and was damn right unprofessional.Such is the state of education in the UK, it's absolutely atrocious. I can almost agree with the snobbery and class attitude over where your degree came from but then I don't understand why there is not consistency other than this is now a privatized industry.

author: Simon
author_rank: Unknown
timestamp: January 11, 2024, 09:10:27 am
content: Quote from: Siwastaja on January 10, 2024, 05:15:25 pmMaybe one day I will have the time to go through the material in a video and upload it to youtube.