OHM's Law Quiz

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Yako

Joined Nov 24, 2011
245
As I posted in the other thread, one solution is:
Rich (BB code):
It = 0.1 Amperes (declared)
Junction between R4 and R5 is now declared as node N1
Junction between R2 and R3 is now declared as node N2
Vt = 5 Volts          (known; given in problem statement)
Rt = Vt/It            (50 Ohms)
VN2N1 = 1.35          (V(N2)-V(N1), known; given as 1.35V in problem statement, given a name for calculation purposes.)
R3R4pct = VN2N1/Vt    (27%; calculate percent of total)
RR3R4 = Rt * R3R4pct  (R3+R4 = 13.5 total resistance)
R6 = RANDOM(Rt-RR3R4)         (R6 is a random number between 0 and 36.5 inclusive)
R5 = RANDOM(Rt-(RR3R4+R6))    (R5 is a random number between 0 and the sum of R6, R4, and R3)
R2 = RANDOM(Rt-(RR3R4+R5+R6)) (R2 is a random number between 0 and the sum of R6, R5, R4, and R3)
R1 = Rt - (R2+RR3R4+R5+R6)    (R1 is the remaining resistance, if any)
R4 = RANDOM(RR3R4)            (R4 is a random number between 0 and RR3R4)
R3 = RR3R4 - R4               (R3 is whatever's left of RR3R4 after R4)
Seems about right.

Any other solutions that we can think of guys?
 

Yako

Joined Nov 24, 2011
245
My solution:
Rich (BB code):
IT = 1mA
RT = V / IT
= 5 / 1 exp -03
= ~5K

R3 & R4 series combined = (VR3 / V) X RT
= (1.350 / 5) x 5000
= 1.35KΩ

R3 = 1KΩ
R4 = 350Ω

R1 & R2 series combined = RT - (R3 + R4) / 2
= 5000 - 1350
= 3650 / 2
= 1825Ω

R1 = (R1 & R2 series combined / 2)
= 1825 / 2
= 912.5Ω

R2 = (R1 & R2 series combined / 2)
= 1825Ω / 2
= 912.5Ω

Therefore ...

R5 & R6 series combined = RT - (R1 + R2 + R3 + R4) 
= 5000 - 3175
= 1825Ω

R5 = (R5 & R6 series combined / 2)
= 1825 / 2
= 912.5Ω

R6 = (R5 & R6 series combined / 2)
 = 1825 / 2
 = 912.5Ω
 
-----------------------
R1, R2, R5 & R6 = 912.5Ω 

R3 = 1K
R4 = 350Ω
 
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Yako

Joined Nov 24, 2011
245
Not so easy that one if you have to formulate it all.

I guess that the easiest approach is the first figure out what the (n) voltages for all of the other resistors should be from the given the 1.35V.

Mine & the SGT's solution is too complex.

Can someone suggest something simple?
 
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Wendy

Joined Mar 24, 2008
22,141
And it tends to be among the most high tech electronics you can image, from communications, encryption, to target acquisition and flight control. Pretty much the whole shmere.
 

Yako

Joined Nov 24, 2011
245
Both of my grandfathers were in WW2.

My father's father was in the Navy as a machine gunner.

They both lost the plot a bit when they came back from the war.

My father's father was in the madhouse for a while too.

Couldn't be easy putting bullets in people over politics.

I have all of their medals left to me.
 

thatoneguy

Joined Feb 19, 2009
6,359
Off the topic...
but

How much Navy requires concerning electronics?
Do you mean "Jobs Within the Navy that are related to electronics"?, There is an MOS list somewhere, but it is a huge list. Especially the newer ships that are crewed smaller, but have doubled their electronics capability to make up the difference.

Since Navy was brought up, and I know we all like cool videos of helocopters... http://www.youtube.com/watch?v=bC2XIGMI2kM&feature=player_embedded (Rough Sea Helicopter Landing)

Those are quite capable boats.
 

strantor

Joined Oct 3, 2010
5,253
Off the topic...
but

How much Navy requires concerning electronics?
The navy has really cut back on the electronics training. I never saw the NEETS modules until after I got out of school and someone on the sub gave them to me. When I was in, my chief (was in the navy for 20 years before I joined) said that when he went through training, they actually trained him in electronics. He would always complain about that, that the navy wasn't training their guys and now the burden was on him to train. I made it my whole way through the navy without knowing what an opamp is. All the troubleshooting was board-level only. We would swap boards out of racks (everything has an identical backup system) until the problem moved, and when it moved, we knew the board was bad, and we would have a new board expedited to replace spares; We had duplicates of all the boards on the sub. but we never troubleshoot the boards to component level. there were no components onboard to replace them with, or test equipment to troubleshoot with; well, there was an oscilloscope that nobody knew how to use, and a simpson analog meter. The only time they came out of the cabinets was for annual PMs on them.
The training I got (joined in '04) for electronics was 3-5 weeks of sitting in front of a PC, clicking "next". The PC had some kind of "prototype" board attached to it that you would snap sample cards into. the computer would send signals to the card and you had to use a multimeter to take measurements and enter into the PC to see if you measured right. if you had a question, there was an "overseer" (not instructor) who also didn't know anything about electronics who could "help". So, about 4 weeks of measuring resistor voltage drops and then 4 weeks of "tactical Network Computer Operator" class - basically a condensed A+ cert class also taught by PC. then the rest of my 1.5 years of Navy school was focused on operations - tracking targets with the fire control system - and that they actually taught well.
In retrospect, I guess they knew exactly what they needed to teach me, because we never wound up stranded with a bum system and I was pretty good at tracking targets. They probably pay more attention to the electronics training for guys who work in the repair shops, and the surface fleet electronics techs. On surface ships, they have clear cut operators and maintainers. on subs, you have to be both, so jack of two trades, master of neither.
 

SgtWookie

Joined Jul 17, 2007
22,210
The navy has really cut back on the electronics training. I never saw the NEETS modules until after I got out of school and someone on the sub gave them to me. When I was in, my chief (was in the navy for 20 years before I joined) said that when he went through training, they actually trained him in electronics.
I joined ten years before your chief did, and went through A-schools at NAS Memphis, in Millington, TN. At that point in time, most Navy/Marine aviation-related A-schools were located at both NAS Memphis and NAS Pensacola, FL (consolidated at NAS Pensacola in the 90's).

He would always complain about that, that the Navy wasn't training their guys and now the burden was on him to train. I made it my whole way through the Navy without knowing what an opamp is. All the troubleshooting was board-level only.
You were OMA level (organizational maintenance activity); one usually didn't get to open the black boxes until IMA level (intermediate maintenance activity). It was a bit different working on Vietnam-era stuff.

The radar/missile fire control systems in the F-4J's I worked on used LOTS of discrete components; it was developed in the late 1950's - early 1960's, and IC's didn't really off the ground until the early 1970's. Instead of ICs, the Westinghouse radar I worked on had custom-made small epoxy boxes (maybe 1/2" to 2" in L/W/H) that had discreet components in them, then soldered on a board.

The system had a BIT box (built-in-test), but it was very primitive by today's standards; there was a 35mm program tape inside the box that displayed text as far as which test was being performed, and a whole bunch of dots that were either open or filled in. Light sensors would detect if the dots were filled in or not, and relays were closed or opened to set up the test. If a test failed, the program tape would stop and a "FAIL" light would illuminate. Then you had the joy of tracking down where the real problem was. The BIT box took quite a while to run through all the tests. In a later, digital version of the radar, the BIT ran through far faster; it was controlled by a microprocessor instead of a 35mm tape.

We would swap boards out of racks (everything has an identical backup system) until the problem moved, and when it moved, we knew the board was bad...
Ye Olde 'shotgun' method. ;)

... and we would have a new board expedited to replace spares; We had duplicates of all the boards on the sub.
The only time we had duplicates of all the radar package boards at the squadron area is if we had one aircraft that was "hard down" for something, a "hangar queen". It wound up having a zillion MAFs (did you still have the form 666?) cut against all of the stuff we'd cannibalized from it.

... but we never troubleshoot the boards to component level. there were no components onboard to replace them with, or test equipment to troubleshoot with; well, there was an oscilloscope that nobody knew how to use, and a simpson analog meter. The only time they came out of the cabinets was for annual PMs on them.
It was very different with the old radars we worked on. We may not have opened up the boxes, but we had to know how they worked inside in order to effectively troubleshoot them. "Shotgunning" would often introduce more problems than it fixed with those analog systems.

The training I got (joined in '04) for electronics was 3-5 weeks of sitting in front of a PC, clicking "next".
For some reason, I found that quite funny.

The PC had some kind of "prototype" board attached to it that you would snap sample cards into. the computer would send signals to the card and you had to use a multimeter to take measurements and enter into the PC to see if you measured right. if you had a question, there was an "overseer" (not instructor) who also didn't know anything about electronics who could "help". So, about 4 weeks of measuring resistor voltage drops and then 4 weeks of "tactical Network Computer Operator" class - basically a condensed A+ cert class also taught by PC.
When I went through, it was using all printed materials, and the course was also self-paced. There was a senior NCO available (usually a CPO) if you got "stuck" on something - and they usually knew what they were talking about. You would go through a module, taking quizzes along the way and turning them in. If you were not progressing quickly enough, you would get a visit by above mentioned senior NCO to find out WTF was your malfunction.

When I started the course, I was issued a slide rule. They were very handy to have if you had an itch in the middle of your back. Besides that, I never really "got" how to work them, and when I had the opportunity to buy a used Texas Instruments calculator for $75, I jumped at it. This little electronic marvel had a square root key and a raise-to-power key, and it saved my boot kiester. $75 was a lot of money in those days for a Marine private (E-1) who's monthly pay came to $220. I sold it to someone for $60 before I left Memphis.

I had a hard time with trigonometry. I was stalled on the module for a week before I got "the visit". I finally "got it" after more struggling. Math is not my forte'.

then the rest of my 1.5 years of Navy school was focused on operations - tracking targets with the fire control system - and that they actually taught well.
AFTA (Advanced First Term Avionics) was taught in a classroom, and it was hands-on with actual radar systems in test racks. They weren't the real things we were going to be working on eventually, but they were functional (except the waveguide was rigged to a dummy load and could not be switched to the antenna). We'd spend maybe 3 hours in lecture, an hour in practical, break for chow, and go back for another 4 hours lecture.

That was a really good course; it was over six months long. I had the original texts from the course until I downloaded the PDF's from the Davidson U link - no point in carting those around anymore.

In retrospect, I guess they knew exactly what they needed to teach me, because we never wound up stranded with a bum system and I was pretty good at tracking targets. They probably pay more attention to the electronics training for guys who work in the repair shops, and the surface fleet electronics techs. On surface ships, they have clear cut operators and maintainers. on subs, you have to be both, so jack of two trades, master of neither.
The Navy had to figure out how to train people effectively a long time ago. They know they only have most of their manpower for a few years; in order to remain an effective fighting force, they have to get people trained and into their jobs quickly. It costs a lot of money to train people, and while they're in training, they aren't available for anything else.
 
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Yako

Joined Nov 24, 2011
245
My grandfathers would never really talk to me about the war. My mother's father went a bit bananas if you talked to him about politics.
 

Adjuster

Joined Dec 26, 2010
2,148
I have no Military connections, but de-skilling maintenance, moving from component-level fault finding to replacing modules or whole pieces of equipment is also widespread in civilian life. Of course, here we do not normally expect the sort of tolerance to unavailability of replacements that may be appropriate to fighting a war.

In terms of our own satisfaction, we may feel that this trend away from "Sherlock Holmes" troubleshooting is a bad thing. It may also have bad effects on the consumption of materials. Nevertheless, it is hard to see how this change could have been be avoided, given the evolution of equipment towards greater integration and complexity, and the changing costs of manufacture and repair. Perhaps in a more difficult economic climate there may be a move back towards more repair; time will tell.

I can well understand the sort of frustration felt by an operator who has some real interest in the electronics, but finds him or her self asked to handle equipment as black boxes, with little information about what goes on inside them. There are however reasons that may justify this. One of these is the principle that "a little knowledge is a dangerous thing". Many troubleshooting situations employ a hierarchy of personnel to deal with problems at different levels. This may not be as well defined as say in the Navy, but nevertheless there are boundaries. A well-meaning lower level operator who tries to go beyond their remit in this may do more harm than good.

At one time I worked on troubleshooting in a factory. The line test operators and their supervisors could cope with certain foreseen problems, but beyond that fault reports would be originated and engineers detailed to investigate them. One of the engineers' pet hates were the "helpful" operators who tended to record more or less of a diagnosis of the problem, often based on misunderstandings of how the product actually worked, instead of simply stating what had been observed. This was addressed by very explicit instructions to operators on how to write things up, but it remained a perennial problem, tending to crop up from time to time when new personnel were recruited.

One result of this sort of situation may be a preference for employing staff who do not possess any knowledge beyond what is actually required of them, and actively discouraging them from learning any more. I doubt if this is really a good approach, particularly as it may not help motivation.

In the end, the real difficulty may lie in getting people to have a realistic idea of how much they actually know, rather than exactly what level that might be. I really have no clue as to how that may be arranged: it is only necessary to read some of the enquiries that come to this forum to see that, to coin a phrase, "There are known knowns; there are things we know we know. We also know there are known unknowns..."
 

SgtWookie

Joined Jul 17, 2007
22,210
Sounds like you had a wonderful time Sgt.
It took some getting used to ... but things improved enormously after I joined an all-volunteer Marine Drum & Bugle Corps we had on base there. It wasn't long afterwards that all the D&BC participants were moved into the newest accommodations on base; we even had a beer machine in the barracks on the 1st floor (stateside Marine barracks simply didn't have beer machines, but this was a Navy base, and the 1st floor was Sailors).

Band members had a fantastic time. We'd play a gig somewhere, and afterwards go on liberty in our Dress Blues. We escorted the ladies for the Miss Arkansas contest (they don't let Marines do that anymore; it stopped in 1993 - too many parents were mortified that their darling daughters turned up pregnant :eek:) We were flown in USMCR (reservist) CH-53 helicopters from Memphis to Philadelphia to play at the dedication of the Bicentennial Building.

We really had a blast. When we had a long weekend, we'd pool our resources and take off cross-country to someplace we hadn't been. Lots of adventures and hilarity ensued.
 

SgtWookie

Joined Jul 17, 2007
22,210
My grandfathers would never really talk to me about the war. My mother's father went a bit bananas if you talked to him about politics.
Veterans who served in ground combat very seldom share what they experienced with anyone other than Veterans who went through similar experiences. They usually speak in hushed tones, away from the others - and if a non-ground-combat Veteran approaches, they will change the subject, or simply remain silent until they are again alone.

I did not experience combat, and I am frankly quite glad that I did not have to endure that kind of traumatic experience. The "Great Asian Vacation" was still going on when I enlisted, but was over with by the time I finished with my schools.

I don't ask Veterans who have seen combat to share their experiences; it is very poor form to do so. All you can do is make the Veteran feel at home and appreciated. If they feel comfortable enough to share (which is still highly unlikely), they will - but it must be left up to them.
 

Yako

Joined Nov 24, 2011
245
They must have gone through hell. My mother's father gave up drinking when my grandmother had her first heart attack. All he would really ever tell me is that war is a terrible thing.

Served in WW2. Drunk most of his life. Heavy smoker. Almost saw his 80th birthday.
 
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