24-09-2008, 05:44 PM
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.