Electronics > Beginners
KVL and KCL Equations
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RoGeorge:
The circuit and the values are obviously made for mental calculations.

No need for KVL, programs or computers:  There are 2 resistors in parallel, then connected with a 3rd one in series.

R|| = 20 || 80 = 20*80/(20+80) = 1600/100 = 16  \$\Omega\$
R total = 16 + 4 = 20  \$\Omega\$
I source = 200/20 = 10 A

Ia is 4 times bigger than Ib, and together are 10 A, so

Ia = 8A
Ib = 2A
Vo = 2*80 = 160V
GerryR:
Yeah, back in my fossil days, they would say that the solution(s) were "intuitively obvious," and then after two or three pages of calculations later, maybe it was somewhat obvious. ::)  In this case, I agree with RoGeorge that the values were made for quick mental calculations and to give the student some training in recognizing different component combinations to simplify analysis.
rstofer:
I agree, the point is building the equations.  There are at least 3 ways of writing the mesh equations (and I don't think there are more) and just 1 way to write the node equation.  In school, we seemed to focus on KVL but in many cases KCL is easier and may involve fewer equations.

The numbers were neat but the magnitudes were gross.  We simply don't work in Amps and Ohms, it's more likely mA and kOhms.  Volts aren't in hundreds, they're down around 5 or 3.3.  It doesn't matter, it's the process of writing the equations that matters.

I can hardly wait for the AC circuits!

"Intuitively obvious to the most casual observer!"
Tom45:
My college years far predates Matlab or equivalent. So I've never had any experience with what seems to be a common tool now.

However ECAP is very familiar to me. In 1966 I ported ECAP from IBM 1620 FORTRAN II to CDC 3300 FORTRAN IV. Source was 4 boxes of punched cards. Once ported, I wrote an introductory user manual for it. Needless to say, I remember nothing about the details of using it. But I do remember many of the general features such as sensitivity analysis. 4 boxes of punched cards was somewhat less than 8000 lines of source code. Amazing what ECAP could do in what today would be a tiny program.

I later ported MIMIC, an analog computer emulation that ran on digital computers. I don't remember the source computer, but the target was again the CDC 3300. The last job of that trilogy was to port CIRCUS, a more advanced program that ran on an IBM 7094. It used quite a bit of 7094 assembly language which made the task a lot harder. I never finished it as I was reassigned to something else. I doubt anyone else ever attempted to finish it either.
rstofer:
I'm a little behind you, I started college (again) in 1969.  I was playing with the IBM1130 by 1970 and I well remember carrying a box of cards from my office to the computer lab about 1/4 mile away.  Did it all the time.  Came in on weekends to work on homework.  I spent so much time there the manager was beginning to think he should just hire me.

I also had the source to ECAP and I think I still do.  It's been a couple of years but I think I have it running on my FPGA version of the 1130.  I also have CSMP, the Continuous Systems Modelling Program.

I also had some restricted access to the CDC 6400 but the cost per minute was so high I didn't use it much.

The IBM1130 was my first computer and is still my favorite.  It was amazing what you could do 8k words of core when you go clever with overlays.

I graduated in '73 and did grad school in '75-'76, right at the very beginning of the microcomputer era.  It's been an amazing ride!
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