Kirchoff's Laws...

I myself came out of ten years in the real world before going back to school. Granted, not as an engineer, but IT is hardly low-skill. Also, seeing as I'm a physics major now, I've been focusing more on the theoretical. Don't forget that physics grew straight out of engineering and is now the backbone of it.

I've been questioning my decision to go for physics, because I want to build things, too. I just think my own ends will be met better by this course.

Besides, I have my own idea about the value of theory vs. practice, and how the "dead men" really knew what they knew.

Just keep in mind that my analog group partner(there's only 2 of us here) is a MS in Physics.  He is now an RF designer like me.

> SPICE and simulation tools(every day!)

Basic SPICE is Kirchoff. You define nodes and links, it sets up KVL and KCL equations, inserts the known values, and solves for the unknowns.

> The ability to sort through datasheet marketing BS(every day!)

In some rackets, that should be #1.

On another plane, you can pretend that anything invented after 1950 (or 1933, or 1910) is the same old stuff, nothing new.

Except maybe the price. Or lower losses.

Tubes make fine audio amps. Transistors do it cheaper and cooler. Tubes make fine 10MHz amplifiers. Transistors have smaller parasitics and go past 100MHz easily. An iPhone built with tubes might be bigger than Apple Headquarters; there IS "progress". Or at least change. But all incremential. XYZ Corp's new BS123 chip is not the Dawn Of A New Era.

> I think I used Diff eqs once too.

Not me!

I do sometimes list a bunch of values, then note the difference between each one, and look at that trend. As I understand the Differential Engine, it does the same thing, with a crank.

PRR said:

 
Consul is so new-to-this, he thinks a Professor can help him. Same Prof who already confused him.

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Svart said:

I had a couple professors that were really awesome but most were exactly as you describe.  Even the awesome profs were a little too academic to really get into the details that we need.

I have to admit that I learned more from the first year on the job working under a couple of very friendly and supporting senior engineers than I did in any combination of classes from any of the schools I went to.

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Two points caught my eye.

That is why I think a lot of university level text books which are written with only the academic language in mind suck. All the information is there except what you need to be able to get to the point. They miss to give you the "WHYs" and "BECAUSEs".

On real EEs, the trophy goes to a close relative. I was in my early twenties and at that time he was one of the few experts on HV transformers and transmission lines in Turkey, he probably still is. He used to sit down with a cup of tea, a pencil and a simple calculator, work through these complex mathematical models and produce results that we could understand. I think being able to acquire that level of skill has nothing to do with only studying EE or any other subject. Either you have it or not. And I don't.

Consul said:

The big trouble in the class, I think, is how to apply such basic ideas to circuit analysis and end up with useful information. Like I said, I'm getting it now, but some of the other students...

Also, that's describing the Junction Rule. The Loop Rule is the one causing the troubles.

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OK, I'm self taught so I had to figure out what you mean by "loop" rule, but I am guessing after some quick googling what I called the node rule, is Kirkoffs 1st current law, and your "loop" rule is his 2nd voltage or "mesh" law.. Simply put, the voltage around a loop must add up to zero.

No classic analogies come to mind so here's one I just made up that's only a little odd. Suppose instead of voltage we substitute altitude or height above sea level for Kirkoff's voltage. Instead of electronic networks let's think of the roads you travel back and forth to school. Say you ride your bicycle to a school every day that happens to be on top of a hill, 100 feet higher than your beach house. On different days you may take different roads with different slopes and even some that take you higher than 100', but every night you end up at home at sea level or zero altitude. No matter how many ups and downs you travelled in any day, it always adds up to zero altitude. 

The reason the altitude always adds up to zero it's because IT HAS TO! It's the same physical place so it can't be at two different altitudes at the same time. In Kirkoff's circuit loop, that one circuit node can't be at two different voltages at the same time so no matter how you travel around the loop all the ups and downs MUST add up to zero to get you back to the same voltage. This just is.

Perhaps it sounds clearer if we say the voltage around any loop "leaving from a single node, and returning to that same node" always adds up to zero. Of course I'm not so arrogant to rewrite Kirkoff.   

I hope this helps, or at least doesn't hurt...

JR

Well if your conception of space-time was like my mother's you might not be so sure.

When I visited her before she had been moved into managed care at her house in Paradise CA we ventured forth to the market.  When returning I was about to retrace the path, and she said Oh no honey---go this way---it's shorter.

I said Well why didn't we come this way then to begin with?  This was a mistake.

After much arguing she finally said Well I just like to go this way.  Of course I said Well if you had said that to begin with it would have been fine---but saying one path is shorter in one direction and another path is shorter in the other, absent other not-as-the-crow-flies considerations (of which in this case there were none), didn't make sense.

As I say, a mistake.

Yes, but in the spirit of Kirkoff, upon returning home, the net distance travelled "away from" and "back toward" home would equal zero. If we make distance from home the analog for voltage potential this is another Kirkoff loop analog.

JR 

bcarso said:

Well if your conception of space-time was like my mother's you might not be so sure.

When I visited her before she had been moved into managed care at her house in Paradise CA we ventured forth to the market.  When returning I was about to retrace the path, and she said Oh no honey---go this way---it's shorter.

I said Well why didn't we come this way then to begin with?  This was a mistake.

After much arguing she finally said Well I just like to go this way.  Of course I said Well if you had said that to begin with it would have been fine---but saying one path is shorter in one direction and another path is shorter in the other, absent other not-as-the-crow-flies considerations (of which in this case there were none), didn't make sense.

As I say, a mistake.

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So, you walked the Carso valley, did you?

Again, I understand perfectly the concept of the Loop Rule (although your walking path from/to home is actually quite a good analogy). The key is in knowing how to use the concepts to set up systems of equations.

When you encounter a component, is it uphill or downhill? By how much?
Is there another pedestrian there and is he heading in the same or opposite direction as you?

Sure, it's a simple concept, but we humans can make it complicated really quick. Don't worry, though. I have it down pretty good by now.

> When you encounter a component, is it uphill or downhill?

In general, you may not know.

BUT you -pick- a direction. Simple loops like mom's market route, you might decide to always go clockwise. If Mom starts in the other direction, then all vectors are negative, but still sum to zero when the car is back in the garage it started from.

As I say, I cheat. My mind falls in ruts which may look counterclockwise, but I know what sign the result should be, so I'm not lost. Until I hit a contradiction, and have to proof each node. I think the least-stressed process for arbitrary multiple loops is to handle each one clockwise, alone, and then combine the equations (with signs).

Not you, but your classmates, may also not have internalized the notions of voltage and current. Took me years. Will be decades before I would use Kirchoff in public. I don't see how they can take an iPod-raised youth-of-today and make an EE in 5 years. They have to dig Kirchoff the first year, to get through a century of electrical history in a few more years, but it is really too fast.