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2006 question 3 - faulty IRJ
#1
Does anyone know how to do question 3 from the 2006 paper? Or even where to find the information about how to do it? I've got part way through it if anyone wants to compare results, but I've hit a bit of a wall. A colleague and fellow candidate mentioned Kirchoff's laws & simultaneous equations which took me back to my uni days and I could feel my blood pressure rising. Sad
Is there a simple answer to this or do I really need to dig out my textbooks?
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#2
BedfordBoy Wrote:Does anyone know how to do question 3 from the 2006 paper? Or even where to find the information about how to do it? I've got part way through it if anyone wants to compare results, but I've hit a bit of a wall. A colleague and fellow candidate mentioned Kirchoff's laws & simultaneous equations which took me back to my uni days and I could feel my blood pressure rising. Sad
Is there a simple answer to this or do I really need to dig out my textbooks?

In my day Ohm's law Kirchoff's law and algebraic equations were school physics, but yes, these are what you want to use.

Here is an attempt from a student last year


Attached Files
.jpg   2006 mod5 q3-1.jpg (Size: 96.04 KB / Downloads: 328)
.jpg   2006 mod5 q3-2.jpg (Size: 80.3 KB / Downloads: 254)
.jpg   2006 mod5 q3-3.jpg (Size: 79.5 KB / Downloads: 234)
PJW
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#3
PJW Wrote:In my day Ohm's law Kirchoff's law and algebraic equations were school physics, but yes, these are what you want to use.

Thanks, this solution is a lot simpler than I was making it. The crucial step I was missing was calculating the voltage drop across the feed resistor and hence the supply current. As for high school physics, I'm sure you're right but I'm afraid I have even less chance of remembering that than I do university physics. I seem to recall dropping a cricket ball and a marble off a balcony...
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#4
BedfordBoy Wrote:
PJW Wrote:In my day Ohm's law Kirchoff's law and algebraic equations were school physics, but yes, these are what you want to use.

Thanks, this solution is a lot simpler than I was making it. The crucial step I was missing was calculating the voltage drop across the feed resistor and hence the supply current. As for high school physics, I'm sure you're right but I'm afraid I have even less chance of remembering that than I do university physics. I seem to recall dropping a cricket ball and a marble off a balcony...

I have not had sight of the question, but from the format of Peter's student's answer, I am guessing it is almost the same as 1999 Question 1. I had prepared this analysis sometime ago but had not got round to drawing the digarams to go with it, so sorry that they are hand drawn, but I though that was better than nothing!

I am intrigued by peoples fear of Kirchov and the like. They are the tools which make all things possible. We had a module in our first year at uni entitled Engineering Systems Theory which, looking back, is the set of lectures that I draw most heavily on. Much of the semiconductor equipment and microprocessors we learnt about are obsolete now, but the tools that we equipped ourselves with on circuit and systems analysis (although abstract at the time) are still valid whether it be a track circuit or a transistor!

I note that you got stuck because you had not thought about the volt drop across the feed reisistor. If you try to put whatever information you are given into an equivalent circuit (as the wording of the question sometimes requires of you) then all of the elements are more likely to jump out at you!

The attachment here is not intended as a model answer, rather an example of how two different analysis models can be applied to the problem.

Perhaps you'll be brave enough to post your worked answer so that others can compare their approach (and answer).

Peter


Attached Files
.doc   1999_5_1.doc (Size: 219 KB / Downloads: 211)
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#5
Peter Wrote:I have not had sight of the question, but from the format of Peter's student's answer, I am guessing it is almost the same as 1999 Question 1.

I've just been revisiting track circuit calcs and thought I'd have a go at the example from 1999. I made a mistake in that I considered the point at which the current through the resistor falls below the pick-up rather than the drop away current as the failure point. Realistically, I think this is when the tracks would fail, (i.e. they won't pick after the passage of a train), however I note that the question does actually say "with no trains in the area". I guess it just shows again how important it is to read the question properly.

I'll get to the point now - does anyone have a feeling for how many marks would be lost for a mistake like that if the rest of the working was ok?

I've attached my attempt in case anyone is interested, just excuse the handwriting and keep in mind that the answer is WRONG.
Thanks.


Attached Files
.pdf   1999_q1_wrong.pdf (Size: 34.64 KB / Downloads: 157)
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#6
No real idea how many would be lost but if you were in the vicinity of a grade boundary Distinction / Credit or Credit / Pass it would probably knock you down to the lower one. Perhaps it might lose you some 5 marks; however had you put that one liner at the end that you had realised your mistake then reckon would only have lost a couple.
PJW
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#7
FYI


Attached Files
.pdf   2006Module5Exam_paper.pdf (Size: 80.2 KB / Downloads: 24)
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