View Full Version : how I flunked trig

Fred Hawkins
09-12-2007, 11:56 AM
by getting every cosine and sine problem completely wrong by misapplying sine solutions for cosine solutions. I was consistent too, so cosine for sines...

Which is a shaggy dog story way of introducing this latest reincarnation:

I have been mentally pushing electrons out of the + side of a battery (because it's got more of them. Therefore +). And of course, when the prop outputs bits high, my mental construct was squirting electrons willy-nilly out of all those pins.

Tonight I got curious about AND gates that weren't in ic chips but made out regular stuff. After a bit of internet here and there I found myself looking at noobie electricity page of a battery and resistor schematic. With current flow illustrated by a big red arrow. From ground through the resistor and into the + side of the battery. http://www.play-hookey.com/dc_theory/schematic_diagrams.html

But then I looked at wiki's electric current page: http://en.wikipedia.org/wiki/Electric_current·with the red arrow going from + to -.

So. My question to the prop community (and parallax in general): is there a duckies and bunnies rundown on how electricity moves around in a propeller chip and circuits? (A work alike will do. All I want is stand on firmus grundus again.)


09-12-2007, 12:24 PM
Fred, this is a pure convention! As electrons are negatively charged, they HAVE TO move from minus to plus, this is of importance if you need the electrons themselves as in CRTs (and other tubes) where you substantially EMIT the electrons from the cathode!

As it was felt a hundred years BEFORS the invention of the CRT, electric current has to "flow" from somewhere to somewhere, "they"decided that "plus" should be the source: But as always with 50:50 chances it came our wrong...

But note it was the time where most people thought heat was carried by "phlogiston" and an "atom" was a fancy concept of old Greeks..

There is other material moving according to electric fields besides electrons: Ions inside a battery or in other electrolytical substances. You can extend the concept of "moving" things even to model the behaviour inside semi-conductors, where the places move where an electron could be. These "holes" move from minus to plus, obviously, same as positively charged ions.

For the fundamental laws of electro-magnetism the "real" direction electrons move is of no further significance. As what transports the energy are not the electrons (in most cases) but the accompanying electro-magnetic fields...

Post Edited (deSilva) : 9/12/2007 5:29:42 AM GMT

Fred Hawkins
09-12-2007, 12:35 PM
(looking under that bush: no bunnies here. Nope, no duckies either.)

09-12-2007, 12:35 PM
The electrons are the things that actually carry the charge around the circuit, the protons pretty well being stuck where they are.

As we all know, electrons are negatively charged (protons being the positively charged particles). So, the waves of charge (as such) flow via the action of the electrons from the - to the + terminal. Because us humans are such optimists, we·reverse the sense of this "double-negative" (negatively charged particales flowing from the - terminal) to a positive charge from the + terminal.

Even though the energy waves are travelling at the healthy precentage of the speed of light, the electrons themselves move·quite slowly.·I don't quite remember the exact number, but I was surprised when I found out many years ago that most metals will glow red hot with an electron flow rate of·about 1mm per second.

You could probably have a stab at guessing how fast the electrons flow by doing a calculation of E=mc2
E - amount of energy in a battery (or any other source)
c - speed of light
m - total mass transfer
Then divide the total mass transfer by how long the circuit is powered by the battery.

Some of the above may be complete fiction - as it is all being recalled from distant memory (not quite 20 years).

09-12-2007, 12:52 PM
Yes. deSilva is absolutely right.

This "it has to be right - hasn't it?" attitude has caused a lot more confusion than clarity. It is good to know that what we call electrons have a (by convention, also) negative charge. And that current therefore actually moves in the "wrong" direction. But, what if electrons were defined to have positive charges? Then, it would all be OK again.

There are even some universities that think that everything shall be absolutely right. So, they teach electron flow instead of current flow. This has a lot of implications. One is that the well-known right-hand rule (showing direction of a magnetic field produced by current) has to be replaced with a "left-hand rule". Another is that generators consume electrical energy and motors generate it. And lots of other unnecessary complications. Plus the confusion it creates in students that have a hard time grasping fundamental physiscs in the first place.

So. Stick to the convention. It makes life a lot easier. But, of course, YOU know about the real truth.

BTW: An example of how easily one can get confused by the ambiguity can be seen in deSilvas' post where it, too hastily perhaps, is said that "These "holes" move from minus to plus, obviously, same as positively charged ions". Which, as we all (including the esteemed poster) know, isn't true. But shall we really care?


09-12-2007, 02:19 PM
I think of electron flow like a vacum cleaner , one side has more suction.


Fix it if ain't broke·
D Rat

Dave Ratcliff· N6YEE

09-12-2007, 02:34 PM

I heard some many years ago that phogiston was what was lost from a substance or body when it was burnt. Not that was the carrier of heat, but as it was at the University, you know you not always hears everything.... Those where dark times (darker than nowadays), I mean the ones at the Uni !.

Is just a simple matter of convention. Like when you solve circuits with several paths, the current flows through the resistors... it really does not matter in which way if you just make it consistent. Electricity is full of conventions, without those there is not reference point, and one has to start over. Like what happened in those dark times. One man "discovered" something that maybe someone else discovered already, but lack of standards and communication did not prevent double work... Nowadays we are (it seems) at the other end point, too much information clouds (sometimes) valid data http://forums.parallax.com/images/smilies/smile.gif, and pride and self interest make the rest :-(.

History of science is quite interesting, especially because it is all interconnected, chemistry and physics and electricity (as if they were not today!).

Have fun


edit: syntax corrected

Graham Stabler
09-12-2007, 04:06 PM
Fred, unless you are designing semiconductors then forget about electrons and just think about potential difference and conventional current. The +5v is at higher potential (like higher pressure) than 0v so flow goes from 5v to 0v much like a balloon has high potential inside it an when you make a hole the air goes from inside to out or a ball at the top of a hill has high potential and will roll down if given the chance!

The concept of holes as far as I know applies to semiconductors only not metals, metals have an electron cloud and its more a case of sticking an electron in one end and one falling out of the other end, a bit like a row of train carriages or a newtons pendulum. This is why the speed that the electrons move at is very slow compared with the speed of the signals, its a bit like communicating with a long stick, you can prod a person at the other end of the room very slowly but the effect is instant.


Fred Hawkins
09-12-2007, 05:10 PM
Thanks Graham,
I was worried about magic smoke and would be dead pins provoked by sundry recent threads. And to have my ignorance so quickly revealed as that diagram did, FUD raised its ugly head.


Graham Stabler
09-12-2007, 05:21 PM
I wouldn't feel too bad, for that site to show current flowing from negative to positive without an explanation was just wrong. One real problem when it comes to learning is that a lot of the people trying to teach the subject don't really understand it properly themselves.

I had that with mathematics too, we would be taught the basic example for a technique and then given exercises to do, this would program our neural nets so we generally got the answers right but without any real understanding. When I came to revise I looked in a book and found some very simple rules that allowed me to deal with all the unusual examples with ease. Often what is actually simple is made complicated by explanations that don't really hold much water.

It was probably your intelligence and a wish to understand rather than just accept that lead to your troubles with trig.


09-12-2007, 05:55 PM
Fred Hawkins said...
...is there a duckies and bunnies rundown on how electricity moves around in ... circuits?

Maybe there is. Recently, the book There Are No Electrons: Electronics for Earthlings by Kenn Amdahl was strongly recommended to me. I just acquired it, and look forward to an enjoyable read.

Its opening paragraph?

There are No Electrons said...
Some people honestly believe they understand electricity, just as alchemists once thought they understood how to transform lead into gold. Don't despise or ridicule these poor souls. They should be tolerated and gently educated until they are ready to rejoin society.


Chad George
09-12-2007, 06:44 PM
In the Navy's Electronics Technician 'A' School (at least the Nuclear Power side I can't vouch for the other schools) The text books/curriculum explained it that they just labeled electrons wrong they should have been the positively charged particle and protons negatively charged. Because the conventional definition of charge (current) flow already said that something was flowing from positive to negative. When they figured out what the charges were, they labeled them before they knew which was moving. (seems to me like somebody jumped the gun)

The result is now that dc current is conventionally "thought" to flow from positive terminal to negative terminal. It's just that this "current" isn't actually the flow of electrons.
At this point almost the entire class is totally confused. So the correct mental picture is the flow of "holes" or where the electrons aren't. This flow is from positive to negative. Hole flow is what we think of as current flow.

Of course after explaining this they told us that "hole flow" theory makes too many aspiring ET's to fail out of the program so the Navy still uses the normal (wrong) convention of electrons flowing in current. So we were informed that everything we learned would be a farce before they taught it. But they made us learn it anyway.

09-12-2007, 09:24 PM
Take care: electrons do not only flow from minus to plus, but also from plus to minus. To circuit has always to be closed, inside the current source, the electrons flow in the same direction (they do not turn around) but now from plus to minus. As long, as you don't charge your accumulator. And in normal electrical conductors, electrons don't "flow", but "trift". Their velocity is rather low, compared to their thermal vibration speed.

Fred Hawkins
09-12-2007, 09:38 PM
I am reconsidering going back to the Tennessee* Speed Hammer School of Electronics. Which says, if it doesn't work right no matter how much you tune it, give it a wack. The integrated circuit extension course says, if it gets hot you're doing it wrong and if it smokes you've really done it wrong. Collorary: if it's neither hot nor smoking maybe you forgot a wire, so see if it works anyway.

*my first instructor (Army's HF Xmtr Repair 32C) was from that state, this is most of his wisdom that I retain.

09-12-2007, 11:51 PM
(a) rjo_ gave this entertaining link some weeks ago
web.mit.edu/smcs/8.02/lecture9-220k.ram (http://web.mit.edu/smcs/8.02/lecture9-220k.ram)
Prof. Levien explains Ohm's law

(b) Of course do electrons stop and return http://forums.parallax.com/images/smilies/smile.gif Think of loading and unloading a capacitor, or of AC in the first place.

(c) And electrons are NOT a myth. Everyone having used a tube - and I think there are many of us! - has to believe in them http://forums.parallax.com/images/smilies/smile.gif I think much if today's confusion cames from the fact that radio tubes are no longer taught at universities.

09-13-2007, 01:40 AM
Years ago (many) in a basic electronics course I took while in the Navy, the instructor made reference to "fluidics" as an alternative to electrical and electronic circuits that could provide the same kind of control without the use of electricity. He went on to describe the "analogs" of discrete electronic components and circuits in fluidics. It turns out that the same relationships that follow Ohms Law in electrical circuits, also apply to "plumbing" if you use pressure as an analog for voltage and volume (of flow) as an analog for current and "pipe" diameter as an analog for resistance (it helped me to understand series and parallel resistive networks and RC circuits, finally). Plumbers and electricians have a lot in common when designing systems.

For some reason, visualizing a hydraulic pump as an analog for a battery and then following from there to components and circuits (resistors, capacitors, inductors, fluid amps, fluid logic gates, etc.) just made it easier for me to understand what was happening in a circuit.

Even today, I fall back to "plumbing" analogs when I'm having trouble understanding what's happening in a particular circuit and how I need to modify it for my purposes.

I hope this helps,·· Steve

Post Edited (Duffer) : 9/12/2007 9:53:44 PM GMT

Fred Hawkins
09-13-2007, 12:43 PM
deSilva said...
(c) And electrons are NOT a myth. Everyone having used a tube - and I think there are many of us! - has to believe in them http://forums.parallax.com/images/smilies/smile.gif I think much if today's confusion cames from the fact that radio tubes are no longer taught at universities.
Maybe. But teaching them would create different confusions. For instance, in the jargon of tube users, you heat up a cathode to send electrons to the plate (anode).·And so, in·tube diagrams an anode looks like a plate seen on edge. http://www.allaboutcircuits.com/vol_3/chpt_13/3.html

Fast forward to now, same terminology: cathode/anode, different item: the·LED (and diodes of all types)·and its diagram. Which is the anode? If you're a tube guy, you get it wrong until you get mad enough to remember that these modern guys are idiots. (And they got it backwards).· http://en.wikipedia.org/wiki/Image:LED_symbol.svg

On the other hand, maybe these guys only got the names wrong (but see red note*). Take a look at this picture that brings Duffer's fluidics to life: http://en.wikipedia.org/wiki/Image:Diode_analogie_hydrodynamique_passante.gif (http://en.wikipedia.org/wiki/Image:Diode_analogie_hydrodynamique_passante.gif)· The current flow is just like what a tube diagram (and its user) expects. (I like this gif a lot; it even provides for breakdown current in a physical sense.)

*Mixed metaphor warning!!· That thought is misleading (or just wrong). The LED anode, like the tube anode, is on the plus side of the circuit.
The solid state diagram is more interested in having an arrow head than a picture of a tube.

So now I·don't know what to do. I've·tube cathodes spewing electrons at plates with a higher potential (Graham, that's from my 1970's training, so we agree sort of)·and current flowing from B+ to ground (and through an·LED's anode to its cathode. Even writing the last bothers me.)·Teaching tube theory might not be such a good thing.

But like the fat lady sings, there's no fighting city hall --·diagrams·are all·convention and agreed upon understanding. The simplest thing to do is to toss out the old and relearn new.·Eventually the geezers die off and so·does the confusion.

Post Edited (Fred Hawkins) : 9/13/2007 7:32:56 AM GMT

09-13-2007, 01:12 PM
"Toss out the old"


It is not something you can just "toss out". It is like going from driving on the right hand side to driving on the left hand side.

First: All must agree to do the same thing at exactly one and the same time. Will that be possible?

Second: Lots of roads, entrances, parking places, traffic signs, maps, GPS programs and most of the infrastructure has to be changed. It is "easy" along roads - but how do we handle books and internet sites? Throw out old books? All at once?

Third: You need to agree on it within a whole nation. Would that be possible, given the discussion in this small and quite homogenous group?

Fourth: There are quite a few laws and rules to be changed. Electricity influences many disciplines. It isn't only electric laws that have to be changed.

Fifth: Do not allow anyone to "fall back" into old behaviour. Also a problematic theme. See how the Brits still use pints and feet.

I do not even think it is wrong using the convention we use for current direction today. It is just a convention. Like some countries driving to the left and some driving to the right. As long as you accept the rules, you are fine.

BTW: We did exactly that (changed from left to right hand side driving) back in 1967. But we did it because most of the rest of the world had the "right" convention - not because it was right to do so.


Fred Hawkins
09-13-2007, 02:44 PM
Aha! moment. Or to quote someone smarter than me: Eureka!

Check this out: http://www.rare-earth-magnets.com/magnet_university/conventional_vs_electron_flow.htm

09-13-2007, 02:54 PM
In my country we drive on the right, but trains still go on the left... remainders from a period where they belonged to the British. Marmalade still comes in 1 pound flasks, but labeled as 454 g (I know 1 pound is 453.59 g). Screws, nails, pipes and wood are all in imperial units... besides the metric system is the official one and the one everyone knows, they copied the DIN but did not change everything. (Our television system is also a hybrid PAL/NTSC: PAL-NC). I think there are a couple more oddities, but I don't remember...

Tracy Allen
09-13-2007, 03:14 PM
Fred, at the risk of adding more confusion, take a step into abstraction. Electrical networks are made up of real batteries and real resistors and propellers etc., but the analysis of networks takes a step back. You can call the circuit elements duckies and bunnies if you want. It could really help to do think like that, because it takes away the preconceptions about which way physically current should be flowing.

Network-speak deals with loops and nodes and Kirchoff's laws: Imagine that you have a ducky and a bunny connected in a circuit. Each has two terminals, and the two heads are connected and the two, uhhh, tails, are connected. For network analysis, you start by assigning reference directions. You mark a + on the two heads and a - on the two tails, and on each one you draw an arrow from the + to the -, head to tail. Those are called "associated reference directions". It is an indication of where we will put the red and black probes of the voltmeter if we measure the voltage across the bunny or across the ducky. And if we measure the current, which way the current probe will go into the circuit in each case. It has nothing to do with the way current will actually end up flowing in the circuit. In fact, my two arrows are pointing in opposite directions in the bunny and in the ducky, so when I make the measurement with a current meter, I will find that one current will read the negative of the other. If I substitute a battery for the bunny, and put it in one way, my voltmeter will read positive, and if I put it in the other way, the voltmeter will read negative, with respect to the associated reference directions that I assigned. The assignment is arbitrary. I could have put the - on the head of the bunny and the + on its tail. And reverse the voltmeter leads. The main point is that everything comes out consistent in the end. That has to do of course with writing down the equations that govern the circuit using Kirkoff's laws. If I reverse the reference directions on the bunny, that will all come out in the wash in writing down the equations. But that is probably coming too close to cosines and sines! The real advantage of this abstraction is when the network becomes very complicated and has lots of bunnies and duckies and multileg hefelumps connected this way and that. The same procedure is followed to assign associated reference directions, and that is the starting point for circuit analysis. Kirkoff's laws dictatethe sum of voltages around loops (zero) and the sum of currents into a node (zero).

Each bunny and ducky and hefelump will have a "consititutive relation" which is just a fancy term for things like Ohms law for a resistor or I=C dV/dt for a capacitor, or the IV curve of a diode, and it is those constitutive relations that get plugged into the terms that come from the Kirkoff network anaylsis. The physical mechanism of current flow and voltage plays very little role in this, although that can be very important in understanding the constitutive relation of individual devices.

Tracy Allen
www.emesystems.com (http://www.emesystems.com)

Graham Stabler
09-13-2007, 03:18 PM
Fred, there is nothing really to get so excited about, essentially current travels from + to negative and that's all you ever need to know unless you are dealing with electrons themselves and all you need to know then is that they travel from - to +. The beginning of the video that DeSilva posted is pretty good because he says "positive charge travels from + to - and we say that the current travels from + to -, negative charge travels from - to + but we still say that current travels from + to -" so even though nothing actually moves from + to - in a metallic conductor there is still that effect because of the movement of negative charge.

Anyway I'm flogging the proverbial dead horse because you have found an explanation that suits you, now do we move on to trig? :)


09-13-2007, 04:19 PM
Yes. we could discuss the wisdom of using degrees, grads or rads... http://forums.parallax.com/images/smilies/smile.gif

And then discuss if "sinus" (sine for English readers) really looks like a bay. And some other terminology themes. Probably to find out that we use words and definitions without thinking too much about their real meaning. Which I think is quite acceptable.


Fred Hawkins
09-13-2007, 05:25 PM
Free book, all in pdf's by the same guy who wrote up the bit on 'conventional vs electron flow' linked above. Inoculated with the same virus as many here, it seems. Recommended.


Tracy, let's leave the duckies and bunnies stay on the cover and use crayons for the harder parts. Kulphadt's book does get into network theory by the way. Kirchoff gets heavy mention too.

Graham, I have spent the past 40 years avoiding that conversation. Successfully except when I tried to do matrix math for 3d imaging. Like songs I guess, of which I know none because I can't carry a tune in bucket. Or remember the words any further than the time that they happen. I can, however, if placed anywhere on the Delaware River north of Port Jervis, tell you exactly what turns and rapids are upstream and downstream. As you can imagine, I avoid karaoke bars.

Skogsgurra, that said, I do like rads a lot. I once wrote a submarine game in less than 100 program steps for my TI-55 calculator using polar notation for positioning the ship and sub. If you got sunk the program divided by 0 to get a flashing 9's end. Distance and angles are enough for lots of stuff and forego x,y,z. Rads aren't far from polar coordinates.

Post Edited (Fred Hawkins) : 9/13/2007 1:22:04 PM GMT

David Cary
09-25-2007, 07:56 PM
Fred Hawkins said...
I have been mentally pushing electrons ...

William Beaty has been collecting a huge list of misconceptions.

"Red and green "electricity" (http://amasci.com/redgreen.html)
by William J. Beaty 1994

"Which way does the "electricity" really flow?" (http://amasci.com/amateur/elecdir.html)
by William Beaty 1996

"Ben Franklin should have said electrons are positive? Wrong." (http://amasci.com/miscon/eleca.html#frkel)
by William Beaty

I hope you find these as informative and entertaining as I have.