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
