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Talk:Circuit Idea/Walking along the Resistive Film

A dedication to my students
''I dedicate this exciting story to my students from Faculty of Computer Systems, Technical University of Sofia, spring 2008, that have inspired me to carry out this incredible experiment on the laboratory and to tell about it on Circuit idea wikibook. Cyril''

I have been teaching analog circuitry for more than 24 years. During this period, my students and I have been carrying out many and many times this attractive computer-based experiment (it is my favorite experiment): visualizing the voltage distribution along a linear resistive film that is supplied by two voltage sources connected to the two sides of the resistor. For this purpose, we use all kinds of "resistors", some of them quite odd: resistive wires, pencil graphites, conductive foam and rubber, and of course, opened potentiometers and the good old rheostats. By sliding on the resistive surface and varying consecutively the two supply voltages, we "invent" various legendary resistive devices: movement sensors, voltage dividers, resistive summers, subtractors, Wheatstone bridge, op-amp inverting, non-inverting and differential amplifier, etc.

In addition, this marvelous experiment presents in an attractive non-traditional way the famous Ohm's law, virtual ground concept, negative resistance phenomenon, etc. to curious students. It even shows directly in a "geometrical" way classical relations between the electrical quantities (I = V/R, UOUT/VIN = -R2/R1, etc.) Furthermore, this experiment establishes a connection between the elementary passive resistive circuits (voltage divider, resistive summer, etc.) and the more sophisticated electronic op-amp circuits (non-inverting amplifier, inverting amplifier, etc.)

I have been having responsive, clever, curious and capable students that have been helping and inspiring me in my pursuit of revealing the truth about resistive circuits through these years. That is why, I have decided to place this experiment first on my site of circuit-fantasia.com and then on this wikibook.

Students

During this term I teach basic circuitry (both lectures and laboratory exercises) to 150 students from Faculty of Computer Systems, Technical University of Sofia. They are divided into five groups (64, 65, 66, 67, 68), each of them containing 30 students. Further, for the purposes of the laboratory exercises, these groups are divided into sub-groups of 15 students. Each laboratory cycle lasts two weeks: the first five sub-groups (64a, 65a, 66a, 67a, 68a) conduct laboratory exercises during every even week; the other five sub-groups (64b, 65b, 66b, 67b, 68b) conduct laboratory exercises during every odd week. My general idea is to carry out the same experiment in the laboratory consecutively with all the student groups during the present cycle (March 17 - 29, 2008).

Organization
Preparation. First, in the beginning of the week, I started this story on Circuit idea. For this purpose, I outlined briefly (about 25%) the future page: I traced out the contents by inserting the main subtitles; then, I placed semi-drawn pictures and a little explanatory text. By the way, it was very hard for me to refrain from making the whole page...

In the laboratory, I prepared all kinds of resistive elements (wires, pencil's graphites, conductive foam, etc.), power supplies, movements, VOM's, holders, etc. and arranged the laboratory equipment according to the future experiment's purposes.

I also prepared all kinds of recording equipment - a small solid state recorder (for quite a while I have recording my lessons, classes and laboratory exercises), camera and mobile phone. Maybe, next year I have to use a web camera:)?

I have also begun thinking who of famous web writers (mainly, university and college teachers) to invite to join this educational web initiative. For now, I have in mind Tony Kuphaldt (Lessons in electric circuits), Tom Hayes (Student manual for the art of electronics - great book!), William Beauty (Science hobbyist] - great site!)...

Announcement. Then, in the lecture hall, I announced my intention to conduct such a web experiment to students and showed them how can we carry out it. I told them what is the great Wiki idea and how they can join the wikibook Circuit Idea. I suggested to students to choose meaningful user names consisting of student name and group number (thus I can observe their web achievements and add more credits to the rating).

A chronology of the laboratory exercises
In this part of the talk page, my students and I describe step-by-step how the laboratory exercises have passed. The great mass of the written is extracted from the records but there is also some fragments that is written directly to this page in the laboratory during the excercises. Note that students make their reports in real time at the laboratory; I make also my "report" on the white board (ten times during the cycle!), snap it from time to time and write it on this page. Students and I make a lot of photos during the exercises; they show drafts on the whiteboard, screen shots, laboratory setups and, of course, the very students.

The idea is first to write up here chronologically what is done in the laboratory; then to systematize and polish these raw materials and place them in the main story. We will use here (and why not in the main page?) a quite informal style. I will mark student's insertions by italic to distinguish them from my teacher's text. Well, let's start!

Group 65a (Tuesday, March 18, 2008, 10.30 h)
The genuine Ohm's experiment

History. What did Ohm carry out in 1826? Do you know? Students: No... Please, let's someone write in the Google's window "Ohm's experiment" or "Ohm's law" to see what is written about the topic. Thank you ......... (insert your name here and make comments to obtain credits); please, make a folder in "Favorites" named "Ohm's law" and put there the most remarkable links.

Let's first consider his genuine experiment and then reproduce it here, in this laboratory, almost three centuries later. This is the first of all the ten exercises of this cycle; so, let's try to reproduce it in the most original form. So, what do we need to carry out it? Silence...

Building the laboratory setup. As far as I know, Ohm has discovered the local voltages along a copper wire that was supplied by a strong voltage source. So, we need a wire, a power supply, a voltmeter and an ammeter. But what kind of wire we need? Bare or insulated? Copper, silver, iron, or other? Student: Silver will work excellent...  We haven't a silver wire, let's try with a copper one:) Oh, it has welded!?! It is so well that the power supply has a current limitiing circuit (2.5 A)! That is why Ohm made a strong voltage source by applying the just invented by Seebek thermoelectric effect! Now, it is clear we need a resistive wire (nitinol, NiChrome, etc.); so, let's unwind a piece of wire (about 50 cm) from a heater. ...... (insert your name here), please, meausure its resistance. The resistance is 10 Ω, so we have 0.2Ω/cm.

Experiment 1. Now, fix the two ends of the wire in porcelain insulated terminals (holders) and apply a voltage (for instance, 10 V) first to the left end of the wire. What can we investigate now in this arrangement? What do we measure with the voltmeter? The usual viewpoint is to think of a resistor as a point, as a something that has not dimensions, as a two-terminal element that has only a property of resistance. But here we have the unique chance to peep inside the "resistor"! What will you "see" along the wire? What will the voltmeter show when we slide it from right to left? What are the local voltages along a resistor, if there is no current? Student 1: Zero... Student 2: 10 V... What is the voltage at the right? Zero... And what is it at the middle? Zero...

Well, let's try. Just touch the wire by the voltmeter probe and move it along the wire to measure all the voltage drops (for now, regarding to the ground)! If you are tired, stick a crocodile clips on the probe, "bite" the wire and move this "slider" along it! The result: everywhere local voltages are 10 V!

Experiment 2. Now, ground the right end of the wire. Oh! The wire is hot! Have I instructed you about all the dangers in the laboratory:)? Include this one: do not touch a hot wire! See the ammeter - it shows 1 A; so, the power is P = V.I = V2/R = I2.R = 10 W. By the way, are these calculations right (has the resistance a constant value)? We see, it is too hard for this thin wire to dissipate the power to the ehviroment and it is heating.

Now, move again the "crocodile slider" along the wire and measure the local voltage drops. As far as I know, Ohm did exactly the same. He moved the probe from one position to other, measured the corresponding potentials, made the difference between them and calculated the ratio (V2 - V1)/(L2 - L1) = (V2 - V1)/(r2 - r1) = dV/dR = I. Thus he has established that this ratio (it was the current I) is constant along the wire; so, Ohm has concluded that V/R = I.

We can see that moving the "crocodile slider" the voltage drops decrease gradully from 10 to 0 volts. What is the input and what is the output quantity here? Eureka! Using the "slider" movement as an input and measuring the voltage drop as an output we have "invented" the legendary (but misnamed) potentiometer, movement-to-voltage converter, sensor... Is it a linear converter? Why? A hint: the resistance is distributed linearly along the wire.

Experiment 3. But why do not we change the role of the quantites? With the same success we can stop the "crocodile slider" at the middle of the wire and then to vary the input voltage as an input and, as before, to measure the voltage drop (regarding to the ground) as an output. Eureka (again)! Now we have "invented" the legendary voltage divider (voltage-to-voltage converter)! What is the relation between the input and output voltage (the so-called "transfer ratio"? We can see directly that VOUT = VIN.L2/(L2 + L1).

Experiment 4. We are ready to do more sophisticated experiments... Are there more interesting points (different from the ubiquitous ground) to fix the negative voltage probe? Of course, we may touch any wire point! Well, let's begin with the middle point: "bite" it with the black (negative) negative "aligator" and slide the red (positive) "aligator" along the wire. Only, first change the unipolar voltmeter with a bipolar one. Why? What might we expect? The result is more than surprising: the output voltage varies from -5 V to +5 V! Eureka! We have obtained a bipolar movement-to-voltage sensor!

Experiment 5. What happens, if we move simultaneously both the voltmeter probes in the same direction? Students: The voltage will not change... Right! They name this "common mode input signal".

Experiment 6. And what happens, if we move simultaneously both the voltmeter probes in opposite direction? Students: The voltage will change... Right! It will even change more rapidly than above. They name this "differential input signal".

Experiment 7. Now stop both the "sliders" and wiggle the input voltage. This is a quite odd voltage divider with flying output. What is the relation between the input and output voltage (the transfer ratio? We can see directly that VOUT = VIN.(L2 - L1)/L.

We can measure the voltage drops along the resistive wire by using more unusual indicators, e.g. electric bulbs. What do you think, is there any problem to supply a bulb in this exotic way? If yes, when and why?

Applications. Where may we see this phenomenon in life? The answer is simple: everywhere where a current flow through bad conductors. In all these cases, a gradually decreasing voltage drop appears across the "conductor". A "car example": if you move the probe lamp along the heater of the rear window, you will see the voltage drop across the resistive wire.

Using the heritage of group 65a
Welcome to the laboratory. The picture on the whiteboard represents the laboratory setup that your colleagues from group 65a have used for reproducing the genuine Ohm's experiment. You can use the results of their laboratory experiment to introduce the next great idea named voltage diagram. It will help us to visualize the voltages that your colleagues have measured along the resistive film.

Introducing the idea of pressure diagram (an opened water circuit)

By the way, we can derive this idea from the well-known hydraulic analogy (plumbing) that we can see everywhere around us. For example, imagine a large vessel filled of water that supplies a long thin pipe; let's first the pipe to be tapped. The question is: "What is the pressure inside the pipe?" And more precisely speaking, "What are the local pressures along the pipe?"

We can get to know, if we drill small holes at equal intervals along the pipe (if we want to be more precise, we might stick vertically thin glass pipes acting as local manometers). The result is expectable for us: all the water levels (accordingly, all the local pressures along the pipe) are equal. This picture shows the pressure distribution along the pipe; we can name it "pressure diagram".

The pressure diagram of a closed water circuit

Now open the pipe; the water will begin flowing. What are the local pressures along the pipe now? At the left end the pressure is maximum; at the right end it is minimum. Our intuition suggests that the local pressures will decrease gradually from left to the right.

Really, the levels of the water bars (accordingly, the local pressures along the pipe) decrease gradually from left to the right. The envelope of the pressure diagram is a triangle.

Conveying the idea of pressure diagram to voltage one
Let's now apply this powerful idea to draw the analogous electrical voltage diagrams. The idea is obvious: if we think of voltage as a kind of pressure, we may present the local voltages by local voltage bars in exactly the same way as we have presented the local pressures along a pipe by a local water bars! As above, the lengths of the voltage bars are proportional to the magnitudes of the local voltages regarding to ground (we might set the zero voltage level at the height of the resistor and then to draw the positive voltage bars above and the negative voltage bars below the resistor's level). The set of these voltage bars forms the whole voltage diagram. We can use the envelope of the voltage diagram instead the very set of voltage bars, in order to simplify the image.

Making a computer draw a "living" voltage diagram on the screen
Basic idea. But it is too hard and boring for us, human beings, to draw all the voltage diagrams when the circuit attributes (voltages and resistances) vary. Because these diagrams have to be not static, dead pictures; they have to be "living" diagrams (animations) that change accordingly to the circuit state. So, wee need a computer that "watches" closely what we do with the circuit under test and builds the according "living" voltage diagram on the screen. Then, let's build such a computer-based system and leave it to do this donkey work:). Then we will only look at the picture on the screen and think about the circuit phenomena behind it!

Components. First at all, we need some computer. It may be humble enough, if only it has some graphical possibilities (for example, the computer that is used in this laboratory to build Microlab system in 1986 is a version of the famous Apple II). Then we have only to connect to the PC buses a few analog-to-digital converters (ADC's) acting as analog inputs and a few analog-to-digital converters (ADC's) acting as analog inputs and our computer-based system Microlab is ready!

Power supply. Note that the analog-digital periphery "sucks" energy directly from the poor computer:); so, it acts not only as a computer but it supplies the periphery too. Then can we supply the very resistive object as well? Can we use the very DAC's to supply the resistor under test? This will allow the computer to control the obect! Only, the DAC's can give maximum 10 mA by their op-amp outputs. So, we can't supply the low-resistive (10 Ω) wire of group 65a!

Resistor. Do you remember the linear 4.7 kΩ varying resistor from the previous laboratory exercise? As far as I can remember, we carried out a "reverse engineering" then taking it to pieces:) What do we do now? Suggest a solution!  A student: Yes, I do... Obviously the colleague suggests to supply such a resistor by the DAC's 10 mA outputs without any problem (calculate the maximum current). Thus we can use it instead the low-resistive wire. Then we supplied only the one of the resistor's terminals. Now, let's complicate the arrangement and make it more confusing:) by supplying both the ends (we suspect it might be very interesting). Well, connect AO1 (DAC1) to the right and AO2 (DAC2) to the left end of the resistor.

Voltmeters. What do you think, wheather to connect the two old-fashioned but attractive bipolar voltmeters V1 and V2 to observe the input voltages? Or to rely only on the abstract digital VOM's and the digital meausurements on the screen? I see, you like the good old meters maybe because they are something "live", moving, geometrical, spatial, real... People trust such genuine things... But is there any problem as these "antiques" have 20 kΩ internal resistance)?

Ground. Now, let's say also some words about ground. But what is ground? We can find a possible answer in the Wikipedia article about virtual ground. Shortly, ground is a reference point, regarding to which we measure voltages. The PC power supply that we use is the so called "split supply". It consists of two 12 V supplies connected in series (- + >>> - +). The middle point serves as ground in this arrangement. The DAC's grounds are connected internally to this ground. We have also to connect the black test ends of our voltmeters to this ground.

Software. More than twenty years ago, I prepared a program that can visualize the voltage diagram on the screen as a "living" animation. For this purpose, the program make computer "interest" in the local voltages in three key points - the left end point, the slider intermideate point and the right end point. Let's then satisfy its curiosity:) by connecting, for a start, the DAC1's output to the ADC1's input and the DAC2's output to the ADC2's input.

Group 67a (Tuesday, March 18, 2008, 16.45 h)
The theme of the practical lesson is: Walking along the resistive film The first thing we did on this practical lesson was to reproduce Ohm's experiment, because Ohm's law is the base of the electronics we study. The idea of our practical and theoretical lessons in our course of electronics is to invent everything, every single element (even the resistor). So we started imagining how Ohm did his famous experiment and found the fundamental relationship between the current, voltage and resistance. He did his experiment in the beginning of the 19th century. This means only thing he could use as a power supply was the forerunner of the electrical battery, created by Alessandro Volta. Unfortunately this experiment failed, because Ohm used a wire with very low resistance so the power source was loaded. For reproducing Ohm's experiment we used a resistive wire. In the lab we used a power supply (maximum current 2.5A, maximum voltage 10V), voltmeter and ammeter. So we started the experiments.

Experiment N1:  The scheme we were examining is shown on fig.4 in the main module. We move the voltmeter in this way: one of its ends is connected with the ground and the other is walking on the resistive film by a crocodile clip as a slider. Apparently the measured voltage is 10V no matter where the crocodile clip is along the resistive film.

Experiment N2: The scheme we were examining is shown on fig.5 in the main module. Now we have a change in the measurement of the voltmeter. We can see change is linear.

So now is appropriate to make the hydraulic analog: the tapped pipe and the opened pipe. The illustrations are shown at the main module.

We slide the crocodile clip along the resistive film. This is equal to using a potentiometer. The potentiometer is practically a movement-to-voltage converter. According to the fact that the resistance is distributed linearly along the wire, we can conclude that this converter is linear. So there was a new idea: why don't we stop moving the crocodile slider, leaving it in a certain point on the resistive wire and start changing the input voltage?

Experiment N3: We have 2 voltage sources. One of them (the left one) varies and the other is constant. We see the results on the screen of the computer. You can see the illustration attached it the subtopic in the main module: V1 varies: a left-controlled voltage-to-voltage converter.

$$\ Vout = \frac{r2}{r1+r2}.Vin1 $$

Experiment N4: Now the right one varies and the left one is constant. We see the results on the screen of the computer. You can see the illustration attached it the subtopic in the main module: V2 varies: a right-controlled voltage-to-voltage converter.

$$\ Vout = \frac{r1}{r1+r2}.Vin2 $$

Experiment N5: Now both of the voltage sources vary. We see the results on the screen of the computer. You can see the illustration attached in the subtopic in the main module: Both V1 and V2 vary: a resistive summer.

$$\ Vout = \ \frac{r2}{r1+r2}.Vin1\ + \frac{r1}{r1+r2}.Vin2 $$

As we can see this is a summer with coefficients:

$$\ a = \frac{r2}{r1+r2} $$

$$\ b = \frac{r1}{r1+r2} $$ Since now we have seen the results only when the input voltages are positive. Now we change the polarity.

'''We can see that there is one point we can see on the screen on the computer with zero-potential. This is the famous virtual ground. This point moves on the horizontal axis. So there was a new question – can we make this moving point a fixed one? The answer is yes. There is one element that controls its output in according with the input voltage. This is the operational amplifier. This element keeps the virtual ground at point A. See the illustration: a passive resistive subtractor and of course the negative feedback game.''' Vsj 67gr (I have also placed a copy of this "web laboratory report" on my user page).

 * Virginia, what can I say after reading your excellent material? It is just wonderful! Thank you. I am so glad since my teacher's dreams about joining my students to this exciting wikibooks project are finally realized. Now, you might copy portions of this text that differ from the already written text to the main module. Please, do it until the end of the week; your colleagues from groupe 67a and I might help you. I wish you success. Circuit-fantasist (talk) 09:31, 27 March 2008 (UTC)

Group 64a (Thursday, March 20, 2008, 13.45 h)

Group 68a (Thursday, March 20, 2008, 16.45 h)

Group 64b (Thursday, March 27, 2008, 13.45 h)
Before the exercise our group is very excited to reproduce Ohm's experiments from the past.

Group 68b (Thursday, March 27, 2008, 16.45 h)
In the beginning, we had an "accident" with a $3 Chinese multimeter (VOM) - when we plugged its black test lead into the jack it just went down and disappeared. Then we decided to take advantage of this opportunity and began applying a kind of reverse engineering to it:) Tell here what you have seen inside the multimeter...

More discussions

 * I speak fluent German and I started looking for original works of Georg Simon Ohm -- he lived and worked in the cities where I used to live or stay. Anyway, I was trying to feel the climate where Georg Ohm worked and discovered what now seems obvious to us. Here is his main work - Die galvanische Kette] (in German). I am in the process of reading and don't want to rush thru this fine piece of art. Ohm was a very fascinating person - first, he was a striving bachelor. Suddenly, Ohm got a hold of Volta cell (really, that was a hydrogen cell, right) and established an Ohm's Law by his name with the help of a burner (some question why wasn't he using a Bunsen burner?). However, there was a something called now a Baghdad Battery http://en.wikipedia.org/wiki/Baghdad_Battery My question is: was Georg Ohm the first to notice and/or put it in writing? Ohm's law, I remember, one of my better teachers used to say that Ohms Law can explain almost everything in electronics, regretfully "I have to teach you the other stuff, too'. He was right, look at Richardson Law, how similar it is to Ohm's law or take magnetics...strictly ohm's law... MikeZ (talk) 14:36, 24 March 2008 (UTC)

 * MikeZ, thank you for the link pointing to the remarkable Ohm's work. As I can see, you speak German very well; so, can you read Ohm's publication and tell us (my students and me) what Ohm's laboratory equipment was? What was his voltmeter, ammeter, power supply, etc.? Were they really an electroscope, a magnet needle and a thermocouple? I second your teacher who used to say that Ohms Law can explain almost everything in electronics. I also try to explain almost everything in electronics by using only Ohm's and Kirchoff's laws; my students will say, if I have managed to make it:) Circuit-fantasist (talk) 17:47, 24 March 2008 (UTC)

 * I skimmed quickly thru the book of Ohm -- rather boring treatise. It appears to me that he made every effort to make the simple matters as complex as possible - his revenge on his peers who underappreciated him. It is pretty much mathematical analysis of differential debate of electrostatics around the wire. The whole 280 pages would bore anybody to death. I suspect that this is an afterthought after he came up with his famous equation. As you know most of the works from that time are boring and hard to follow - I guess they didn't have any TV yet so they spent their time writing books.

 * I went thru his other works and I noticed there was something that he wrote about Becquerel, like he was explaining that Becquerel did not do everything the way Oms thought he should have. I started digging and found that:  That is interesting because as you remember Seebeck won a dispute with Ohm later about sound theories. I can imagine Seebeck was not happy that it was Ohm who got the credit for teh 'Ohm's Law'. Also, that article mentions where Ohm got his source of electricity: from Seebeck and I thought he got it from Volta. I have a small refrigerator in my car that I use to keep the food on the way from the store to home. It uses a thermoelectric effect, pretty basic stuff. The switch determines if I want to keep the food warm or cold.

 * (page 155) is a fascinating account on she state of German Physics in the 1820s. Also page 156 confirms my impressions about Ohm's writing. Leitung der Elektricitaet mentions Becquerel working on conductivity of metals.

 * This story tells about Ohm's experiment. The apparatus used by Ohm was as follows. Current flowing through the metal bar in the center cylinder deflects a magnetized needle suspended above it. The deflection angle is proportional to the current. The source of electric potential is a thermocouple (discovered by Seebeck in 1821). The ends of the thermocouple are heated by steam and cooled by ice-water in the small containers on the tripods. The use of a thermocouple made the measurement possible; other sources of potential available in the 1820's were too unreliable." Remember, in those days they did not have $3 multimeters (good to 20A DC) and they did not have batteries. Wire insulation was silk and had to be made by the experimenter. For them concept of current and voltage was abstract, almost revealed by God himself. Not long before they stopped drowning women suspected of witchcraft (there are still in Germany gallows by the roadside left from those days and they look very functional too ;) So in those dark ages, physicists attempted to explain why there were obvious discrepancies between different wires, what was electric current and how it was related to electrostatics. Which way does the current flow anyway? The answer depends on the educational background of the person: academia has one answere and Navy technicians are of different opinion ;)

 * Nothing is cast in stone and much depends on the ability of the school which allows (tollerates) new ways of teaching and explaing. You Cyril are one of the very few teachers who dare to attempt the new. MikeZ (talk) 07:26, 25 March 2008 (UTC)


text:
Circuit Idea/Walking along the Resistive Film

<<< contents - page stage >>>

"Inventing" Various Resistive Circuits by Means of Voltage Diagram

(Reproducing the Famous Ohm's Experiment Nowadays)

Circuit idea: Peep inside a voltage-supplied linear resistor and show the voltage distribution along the resistive film.

"Invented" devices: movement-to-voltage converter, voltage divider, resistive summer and subtractor, inverting amplifier.

Discovered concepts: voltage drop, common mode and differential input, split supplying, superposition, virtual ground, negative feedback.

The beginning: Ohm's experiment
History. Almost three centuries ago, Ohm implemented his famous experiment. In those Dark Ages, physicists attempted to explain why there were obvious discrepancies between different wires, what was electric current and how it was related to electrostatics; for them concept of current and voltage was abstract, almost revealed by God himself. As they say, he stretched a piece of copper wire with length L and resistance R; then, he applied a voltage difference across the wire. As Ohm did his experiment in the beginning of the 19th century, only thing he could use as a power supply was the forerunner of the electrical battery, created by Alessandro Volta. Unfortunately, this experiment failed because Ohm used a wire with very low resistance so the power source was loaded and the ordinary galvanic battery did not work properly. Thus, Ohm decided to make a good voltage source using thermoelectric effect just invented by Seebek. So, the source of a voltage difference was a thermocouple; other electric sources available in the 1820's were too unreliable. Ohm dipped the one end of the thermocouple into boiling water and the other one - into a melting ice put in the small containers on the tripods. Then, using an electroscope (remember, in those days they did not have $3 multimeters:), a magnetized needle and maybe plenty of imagination, Ohm began studying the voltage distribution along the "resistor".

Reproducing Ohm's law. It is very interesting, exciting and important to reproduce Ohm's experiment in the laboratory, because Ohm's law is the base of electronic circuits that EE students study. It would be a great idea, if during the practical exercises and theoretical lessons in electronics courses students and teachers, all together, reinvent everything, every single element (even the resistor). So we started imagining how Ohm did his famous experiment and found the fundamental relationship between the current, voltage and resistance. In this way, reproducing now the famous Ohm's experiment by using present-day measuring devices and no less imagination, we can "invent" various valuable resistive passive circuits.

Building the laboratory setup. In order to carry out Ohm's genuine experiment, we need a resistive wire, conductors, a power supply, a voltmeter and an ammeter. 50 cm piece of wire from a heater having a total resistance of 10 Ω acts as a resistive wire. Insulated copper wires act as condutors. A varying power supply can produce up to 40 V/2.5 A. We will use two kinds of voltmeters and ammeters - old-fashioned movement ones and VOM digital ones.

A tapped pipe (there is no flow)

Let's begin with considering a well-known hydraulic analogy (plumbing) - that we can see everywhere around us. For example, imagine a large vessel filled of water that supplies a long thin pipe; let's first the pipe to be tapped (Fig. 1). The question is: "What is the pressure inside the pipe?" And more precisely speaking, "What are the local pressures along the pipe?" There are not so many people that will answer rightly these simple questions.

We can get to know, if we drill small holes at equal intervals along the pipe (if we want to be more precise, we might stick vertically thin glass pipes acting as local manometers). The result is expectable for us: all the water levels (accordingly, all the local pressures along the pipe) are equal. This picture shows the pressure distribution along the pipe; we can name it "pressure diagram".

An opened pipe (there is flow)

Now open the pipe (Fig. 2); the water will begin flowing. This is a well-known situation from our routine where someone opens a faucet somewhere in the end of the plumbing. At the left end the water pressure is maximum; at the right end it is minimum. But what are the local pressures along the pipe now? Our intuition suggests that the local pressures will decrease gradually from left to the right.

Really, the levels of the water bars (accordingly, the local pressures along the pipe) decrease gradually from left to the right. The envelope of the pressure diagram is a triangle.

An opened circuit (there is no current)
Let's now transfer these notions to our electrical domain, in order to see if the voltages along a resistive wire are distributed in the same way. That means to reproduce the genuine Ohm's experiment under the conditions of today.

Now, fix the two ends of the wire in porcelain insulated terminals (holders) and apply a voltage (for instance, 10 V) first to the left end of the wire (Fig. 3). What can we investigate now in this arrangement? What do we measure with the voltmeter? The usual viewpoint is to think of a resistor as a point, as a something that has not dimensions, as a two-terminal element that has only a property of resistance. But here we have the unique chance to peep inside the "resistor"! What will you "see" along the wire? What will the voltmeter show when we slide it from right to left? What are the local voltages along a resistor, if there is no current - zero, 10 V or something else?

Well, let's try. First, connect the black test end of the voltmeter to the ground. Then touch the resistive wire by the red voltmeter probe and move it along the wire to measure all the voltage drops (for now, regarding to the ground)! If you are tired, stick a crocodile clips on the probe, "bite" the wire and move this "slider" along it! Maybe, exactly in this way, once upon a time, someone invented the true potentiometer... No matter, the result is amazing: everywhere local voltages are 10 V no matter where the crocodile clip is along the resistive film! Obviously, the electrical phenomenon is the same as the hydraulic one that we observed above: the local voltages meausered along the resistive wire connected in an open circuit are the same and equal to the input voltage. But why?

Remember what a resistor does - it "resists". What does it resist? It resists, obstructs, disturbs current by dissipating power. But no current flows in an open circuit. So, there is nothing to resist; the resistor is not a resistor when there is no current. The resistor is a resistor when there is something to resist!

We can apply the idea of a pressure diagram to present in a similar way the voltage distribution along the resistive wire. We can think of voltage as a kind of pressure; so, we may present the local voltages by local voltage bars in exactly the same way as we presented the local pressures by local water bars (Fig. 4)! As above, the lengths of the voltage bars are proportional to the magnitudes of the local voltages regarding to ground (we might set the zero voltage level at the height of the resistor and then to draw the positive voltage bars above and the negative voltage bars below the resistor's level). The set of these voltage bars forms the whole voltage diagram. In future, we will frequently use the envelope of the voltage diagram instead the set of voltage bars to simplify the image.

"Inventing" various resistive devices
Movement-to-voltage converter. Now, ground the right end of the wire. Only, be careful; the wire is hot! See the ammeter - it shows 1 A; so, the power is P = V.I = V2/R = I2.R = 10 W. By the way, are these calculations right (has the resistance a constant value)? We see, it is too hard for this thin wire to dissipate the power to the environment and it is heating.

Now, move again the "crocodile slider" along the wire and measure the local voltage drops; Ohm did exactly the same. He moved the probe from one position to other, measured the corresponding potentials, made the difference between them and calculated the ratio (V2 - V1)/(L2 - L1) = (V2 - V1)/(r2 - r1) = dV/dR = I. Thus he has established that this ratio (it was the current I) is constant along the wire; so, Ohm has concluded that V/R = I.

We can see that moving the "crocodile slider" the voltage drops decrease gradually from 10 to 0 volts; accordingly, the bars of our voltage diagram will also decrease their length gradually (Fig. 5). We can draw such a picture for every real conductor with some resistance that convey big current to a powerful load.

What is the input and what is the output quantity here? Eureka! Using the "slider" movement as an input and measuring the voltage drop as an output we have "invented" the legendary (but misnamed) potentiometer, movement-to-voltage converter, sensor... What is the relation between the output and input quantities? Is the sensor that we have "invented" a linear movement-to-voltage converter? If yes, why? A hint: the resistance is distributed linearly along the wire. Well, according to the fact that the resistance is distributed linearly along the wire, we can conclude that this converter is linear.

Where might we see such sensors? Of course, the most popular application is the fuel tank level sensor where a float moves such a resistive sensor. Only, if you open a fuel tank one day (be careful, it is dangerous!), you will find out that it is non-linear. Can you tell why?

Bipolar movement-to-voltage converter. We are ready to do more sophisticated experiments... Are there more interesting points (different from the ubiquitous ground) to fix the negative voltage probe? Of course, we may touch any wire point! A typical arrangement is to assign the positive rail (+10 V here) as a ground. But maybe the most interesting point acting as a ground is the middle point; so, "bite" it with the black (negative) "aligator". Then slide the red (positive) "aligator" along the wire to the left and to the right of the black one (Fig. 6). Only, first change the unipolar voltmeter with a bipolar one. Why? What might we expect? The result is more than surprising: the output voltage varies from -5 V to +5 V! Eureka! We have obtained a bipolar movement-to-voltage sensor! Of course, another application is a bipolar varying voltage source.

Common mode signal. Let's continue experimenting... What happens, if we move simultaneously both the voltmeter probes in the same direction? The voltage does not change. Why? They name this input "common mode input signal".

Differential input signal. And what happens, if we move simultaneously both the voltmeter probes in opposite direction? The voltage changes even more rapidly than above. Why? They name this "differential input signal".

Measuring the voltage drop by odd indicators
We can measure the voltage drops along the resistive wire by using more unusual indicators, e.g. electric bulbs (Fig. 7), motors, LEDs, etc. What do you think, is there any problem to supply a bulb in this exotic way (Fig. 8)? If yes, when and why?

Do you know that travel hair-dryer and toasters exploit the same powerful idea to supply with low voltage their internal circuits (motors, timers, etc.)? Then let's supply in a similar way a small DC motor (Fig. 9). As we can see, the motor changes its speed proportionally to the distance between the two crocodile clips. Also, if we swap the two crocodile clips, the motor changes the direction of rotation (Fig. 10).

Investigating exotic "resistors"
Pencil graphite. If we are inventive enough, we might investigate various unusual resistive materials to observe the voltage distribution along them. For example, we may supply various loads (including LEDs) by the partial voltage drop across ordinary pencil graphite (Fig. 11); it seems this is a very popular experiment on the web.

Conductive foam. Another non-traditional but very attractive experiment is to investigate the voltage distribution through a conductive foam (Fig. 12). Only, it requires using a perfect voltmeter (why?) But what is the voltage distribution here - line or surface?

Graphite trace. Finally, we can go too far in our sophisticated experiments, if we draw a resistive path on a paper by a soft pencil (the softer the lead is, the bigger the conduction will be) and then slide the voltmeter probe along the "resistor". But don't you think we can even measure the voltage distribution along our human bodies:)? Of course, we need a very, very perfect (high resistive) voltmeters for all these exotic experiments....

How to visualize the voltage diagram on the screen
Basic idea. But it is too hard and boring for us, human beings, to draw all the voltage diagrams when the circuit attributes (voltages and resistances) vary. Because these diagrams have to be not static, dead pictures; they have to be "living" diagrams (animations) that change accordingly to the circuit state. So, we need a computer that "watches" closely what we do with the circuit under test and builds the according "living" voltage diagram on the screen. Then, let's build such a computer-based system and leave it to do this donkey work:). Then we will only look at the picture on the screen and think about the circuit phenomena behind it!

Components. First at all, we need some computer. It may be humble enough, if only it has some graphical possibilities (for example, the computer that is used in this laboratory to build Microlab system in 1986 is a version of the famous Apple II). Then we have only to connect to the PC buses a few analog-to-digital converters (ADC's) acting as analog inputs and a few digital-to-analog converters (DAC's) acting as analog outputs and our computer-based system Microlab is ready (see Fig. 13)!

Power supply. Note that the analog-digital periphery (Fig. 14) "sucks" energy directly from the poor computer:); so, it acts not only as a computer but it supplies the periphery too. Then can we supply the very resistive object as well? Can we use the very DAC's to supply the resistor under test? This will allow the computer to control the object! Only, the DAC's can give maximum 10 mA by their op-amp outputs. So, we can't supply the low-resistive (10 Ω) wire!

Resistor. We can use a linear high-resistive (e.g., 4.7 kΩ) varying resistor instead the low-resistive wire. Then we may supply the resistor by the DAC's 10 mA outputs without any problem (calculate the maximum current). In order to complicate the arrangement, we may supply both the ends of the resistor. So, connect AO1 (DAC1) to the right and AO2 (DAC2) to the left end of the resistor.

Voltmeters. What do you think, whether to connect the two old-fashioned but attractive bipolar voltmeters V1 and V2 to observe the input voltages? Or to rely only on the abstract digital VOM's and the digital measurements on the screen? But the good old meters are "living", moving, geometrical, spatial and real; that is why people trust them. Note they are also bipolar with zero in the middle. But is there any problem as they have 20 kΩ internal resistance)? A hint: the two DACs behave as perfect voltage sources having almost zero output resistance.

Ground. Now, let's say also some words about ground. But what is ground? We can find a possible answer in the Wikipedia article about virtual ground. Shortly, ground is a reference point, regarding to which we measure voltages. Any point inside a compound voltage source can act as a real ground (Fig. 15). The PC power supply that we use is the so called "split supply". It consists of two 12 V supplies connected in series (- + >>> - +). The middle point serves as ground in this arrangement. The DAC's grounds are connected internally to this ground. We have also to connect the black test ends of our voltmeters to this ground.

Software. Now let's start a program that can visualize the voltage diagram on the screen as a "living" animation. For this purpose, the program make computer "interest" in the local voltages in three key points - the left resistor's end point, the slider intermediate point and the right end point. Let's then satisfy its curiosity:) by connecting, for a start, the DAC1's output to the ADC1's input and the DAC2's output to the ADC2's input; then, connect the ADC3's input to the slider. We can control the output voltages of the two DACs by the keyboard arrows; thus the two DACs act actually as programmable voltage sources. The computer measures continuously the three voltages (VIN1, VIN2 and VIN3) and draws three voltage bars whose length is proportional to the voltage magnitudes. Finally, it connects them with a line representing the envelope of the voltage diagram.

For more reality, we might first dismount the varying resistor (the "potentiometer") and touch the measuring probe directly to the resistive film. Now we are ready to continue these amazing experiments. We will use the well-known technique for "inventing" various devices: vary only one quantity at time while keeping the other quantities constant. Let's begin!

Varying V1: a left-controlled voltage-to-voltage converter
Above we were keeping the two voltages constant while varying (moving) the slider position; thus we have "invented" a movement-to-voltage converter. But why do not we change the role of the quantities?

With the same success we can stop the "crocodile slider" somewhere (e.g., at the middle of the wire) and then to vary the input voltage as an input and, as before, to measure the voltage drop (regarding to the ground) as an output. So, the arrangement is as follows: we have two voltage sources; one of them (now, the left one) varies and the other is constant. The result on the screen of the computer (Fig. 16) is amazing - the left end of the voltage diagram rises and drops and all the points along the diagram do the same but with decreasing magnitude (figuratively speaking, we can think of voltage diagram as a second-class Archimedes's lever). We can see directly Ohm's law on this geometrical interpretation:

$$ I_{OUT} = \frac{V_{IN1}}{r1+r2} = \frac{V_{IN1}}{R}$$

Thus, we have "invented" the simplest voltage-to-current converter. But what is more important we have "invented" the legendary voltage divider (voltage-to-voltage converter or "potentiometer") that is controlled here by the left hand side! What is the relation between the input and output voltage (the so-called "transfer ratio"? We can derive it directly from the geometrical interpretation (two nested similar triangles) "living" on the screen - VOUT = VIN1.L2/(L1 + L2). As the resistance r is proportional to the length L (the resistor is linear) we can arrive at a conclusion:

If V1 varies, the resistor acts as a left-controlled voltage-to-voltage converter having a transfer ratio $$\ Vout = \frac{r2}{r1+r2}.Vin1 $$

Varying V2: a right-controlled voltage-to-voltage converter
Above we were "wiggling" the left end of the resistor (the voltage diagram) while keeping the right end fixed at the zero ground level. But why do not swap the roles by "moving" the right end and keeping the left one fixed at zero level? Let's try!

The result on the screen (Fig. 17) is not less amazing than above - now, the right end of the voltage diagram wiggles and all the points along the diagram wiggle too with decreasing magnitude proportional to the distance. Again, we can think of voltage diagram as a second-class Archimedes's lever that we turn from the right.

Thus we have obtained another voltage divider (voltage-to-voltage converter or "potentiometer") that is controlled here by the right hand side. What is the relation between the input and output voltage? The geometrical interpretation (two nested similar triangles) "living" on the screen will help us again - VOUT = VIN2.L1/(L1 + L2). So, the conclusion is similar to the previous one:

If V2 varies, the resistor acts as a right-controlled voltage-to-voltage converter having a transfer ratio

$$\ Vout = \frac{r1}{r1+r2}.Vin2 $$

Varying both V1 and V2: a resistive summer
In the previous experiments, when we were varying some of the input voltages, we were keeping the other voltage equal to zero. But what happens, if we keep the other voltage equal to some (e.g. positive) voltage? And what is more, what happens if we vary the two voltages simultaneously? Let's first suppose they are of the same polarity.

The result on the screen (Fig. 18) is even more amazing than previous ones - by varying the two volages we rise and drop the voltage diagram by the left and both the right. The local voltages along the voltage diagram decrease their magnitude gradually from the lower to the higher voltage source. Now, we can think of voltage diagram as a two-side second-class Archimedes's lever that we turn from the left and from the right simultaneously.

What kind of device have we "invented" now? What is the relation between the input voltages VIN1, VIN2, the slider's position L1/(L1 + L2) and the output voltage VOUT? The attractive geometrical interpretation (a trapezium) "living" on the screen (Fig. 18) will help us again. As you can see, the two parallel sides of the trapezium represent the two input voltages; the internal segments represent the output voltage. You probably can solve this popular geometrical school problem (a tip: draw an auxiliary diagonal) - VOUT = VIN1.L2/(L1 + L2) + VIN2.L1/(L1 + L2). So, the conclusion is similar to the previous one:

If both the input voltages vary, the resistor acts as a passive resistive summer having a transfer ratio

$$\ Vout = \ \frac{r2}{r1+r2}.Vin1\ + \frac{r1}{r1+r2}.Vin2 $$

But this is not a humble summer; as we can see, this is a summer with weighting coefficients:

$$\ a = \frac{r2}{r1+r2} $$ and $$\ b = \frac{r1}{r1+r2} $$

A passive resistive subtractor
We have finally reached the most interesting part of our story... In the previous experiment, we were applying two voltages with the same polarity. But why do not reverse the polarity of one of the input sources? Let's try!

The result on the screen (Fig. 19) is more than surprising and amazing - a point A with zero voltage VA = 0 (regarding to the ground) has appeared somewhere on the resistive film! Note this mystic point is not connected to the real (true, genuine) ground but yet it behaves as such a ground! It is a kind of artificial, virtual ground... Usually, they introduce this concept when explain op-amp circuits. But we can see this is not a unique property of op-amp circuits; it is a property of this simple resistive circuit containing only two resistors. From this viewpoint Ohm could observe virtual ground phenomenon still in 1826, if only he had introduced a second voltage source!

Again, the attractive geometrical interpretation (two similar but now opposite triangles) "living" on the screen will help us to formulate the requirements of existing a virtual ground in a given point. Obviously, the two input voltages VIN1 and VIN2 have to have opposite polarities and they have to bear the same proportion as between the respective resistances r1 and r2 (R1 and R2, if they represent separate resistors): $$ \frac{V_{IN2}}{V_{IN1}} = -\frac{r_2}{r_1} $$

If you like analogies, you might think of this arrangement as an electrical "tug of war", where two voltage sources "fight" each other - VIN1 "pulls" the point A up while VIN2 "pulls" it down. The pull-up resistor r1 and the pull-down resistor r2 serve here as electrical "ropes".

A negative feedback game
What happens, if we begin varying the input voltage VIN1 or VIN2 or both the voltages (keeping VIN1 = -VIN2)? See, the virtual ground point moves left and right! Can we stop it somewhere on the resistive film? If we manage to stop it, we will be able to create famous circuits with negative feedback... Let's try!

Don't you think instead to carry out boring experiments we may play a funny game to imitate a negative feedback system? If you agree with this suggestion, let's cast roles:) One of us ("actor" 1) might act as (be, control) the main independent input voltage source VIN1. The other "actor" 2 might represent the second dependent voltage source VIN2; he/she has to keep the virtual ground immovable. For this purpose, he/she has only to look at the virtual ground point (a zero indicator might help to measure its voltage) and to change VIN2 so that to keep the virtual ground voltage always equal to zero.

The result on the screen (Fig. 20) is just wonderful! The actor 1 (VIN1) tries to move the virtual ground point but the actor 2 (VIN2) returns it to the old position. The voltage diagram rotates around the fixed virtual ground point and VIN2 is always proportional to VIN1; the second voltage follows with opposite polarity the first one: $$ V_{IN2} = -\frac{r_2}{r_1}V_{IN1} $$.

What a great idea! Actually, we may think of the input voltage VIN2 as an output one and we may use it really as an output voltage! This arrangement represents the simplest inverting system with negative feedback.

An op-amp inverting amplifier
As we can see, the actor 2 is bored with this "donkey work" - to observe the virtual ground and to vary VIN2:) Can something else do it? An op-amp seems to be a good choice (Fig. 21). It has a perfect electrical sense; so, it does not need a zero indicator to monitor the virtual ground voltage. Similarly, if actor 1 is got bored too, we can make the computer to produce a periodical voltage at DAC1's output. Well, we can see the op-amp keeps up the same proportion between the quantities as above: $$ V_{OA} = -\frac{R_2}{R_1}V_{IN} $$; thus, we have "invented" the famous op-amp inverting amplifier! Now, we can do a few experiments by changing the slider's position: at the middle point, to the left and to the right of the middle point. How does an op-amp react to this "intervention"? What happens with the voltage diagram? Can we use all these situations to build electronic circuits?

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Prealgebra for Two-Year Colleges/Appendix (procedures)

This appendix contains brief explanations of how to perform arithmetic procedures. We assume that the student has already seen these explanations before and just wants a reminder.

 * To the student
 * Manual of Style

Operations on whole numbers

 * 1) /Adding whole numbers with carrying/
 * 2) /Subtracting whole numbers with borrowing/
 * 3) /Multiplication table/
 * 4) /Multiplying whole numbers with carrying/
 * 5) /Dividing whole numbers by long division/

Operations on integers

 * 1) /Adding integers/
 * 2) /Subtracting integers/
 * 3) /Multiplying integers/
 * 4) /Dividing integers/

Converting between different forms of a number

 * 1) /Reading Decimal Numbers/
 * 2) /Rounding/
 * 3) /Finding equivalent fractions/
 * 4) /Reducing fractions/
 * 5) /Converting improper fractions to mixed numbers/
 * 6) /Converting mixed numbers to improper fractions/
 * 7) /Converting fractions to decimals/
 * 8) /Converting decimals to fractions/
 * 9) /Converting fractions to percents/
 * 10) /Converting percents to fractions/
 * 11) /Converting decimals to percents/
 * 12) /Converting percents to decimals/
 * 13) /Graphing fractions, decimals, and percents on a number line/
 * 14) /Drawing fractions, decimals, and percents as an area/

Operations on fractions

 * 1) /Adding fractions/
 * 2) /Subtracting fractions/
 * 3) /Multiplying fractions/
 * 4) /Dividing fractions/

Operations on mixed numbers

 * 1) /Adding mixed numbers/
 * 2) /Subtracting mixed numbers/
 * 3) /Multiplying mixed numbers/
 * 4) /Dividing mixed numbers/

Operations on decimals

 * 1) /Adding decimals/
 * 2) /Subtracting decimals/
 * 3) /Multiplying decimals/
 * 4) /Dividing decimals/

Vocabulary

 * /Lowest common multiple/ or lowest common denominator
 * /Greatest common factor/
 * /Numerator/
 * /Denominator/
 * /Absolute value/
 * /Exponents/
 * /Roots/


text:
User talk:63.117.55.131

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text:
Prealgebra for Two-Year Colleges/Appendix (procedures)/Multiplication table

 * 1) What pattern do you notice if you fold the table across the diagonal?

 * The numbers are the same on either side of the diagonal; the table is symmetrical.

 * 1) Explain this pattern mathematically.

 * We get the same answer when we change the order of the factors. For example, 8*5 = 5*8. This is called the commutative rule of multiplication.

 * 1) Write this rule in symbolic notation.

 * x*y = y*x

 * 1) What happens when you go across the 4’s row?

 * We are counting up by fours. We add four each time.

 * 1) What happens when you go down the 7’s column?

 * We are counting up by sevens. We add seven each time.

 * 1) Anything times 1 is...

 * ...the same thing.

 * 1) Write this rule in symbolic notation.

 * x*1 = x

 * 1) Anything times 0 is...

 * ...zero.

 * 1) Write this rule in symbolic notation.

 * x*0 = 0


text:
Talk:Myers-Briggs Type Indicator/Criticisms

the skepdic.com analysis is rife with errors and bias, and is not a valid criticism of the MBTI


text:
Cookbook:Turkish Coffee

| Beverages | Cuisine of Turkey

(Turkish coffee: Türk Kahvesi) also known as (Armenian coffee) and (Greek Coffee) are ways of preparing coffee, the best Turkish coffee is made from freshly roasted beans ground just before brewing. A dark roast is preferable but even a medium roast coffee will yield a strong aroma and flavour. The grinding is done either by pounding in a mortar (the original method) or using a mill (the more usual method today), and the end result is a fine coffee powder. Beans for Turkish coffee are ground even finer than the grind used in pump-driven espresso makers; therefore, Turkish coffee should be powdery. It is the finest grind of coffee used in any style of coffee making.

For best results, the water must be cold. The amount of water necessary can be measured using the cups. The coffee and the sugar are usually added to water, rather than being put into the pot first. For each cup, between one and two heaped teaspoons of coffee are used. In Turkey, four degrees of sweetness are used. The Turkish terms and approximate amounts are as follows: sade (plain; no sugar), az şekerli (little sugar; half a levelled teaspoon of sugar), orta şekerli (medium sugar; one levelled teaspoon), and çok şekerli (a lot of sugar; one and a half or two levelled teaspoons). The coffee and the desired amount of sugar are stirred until all coffee sinks and the sugar is dissolved. Following this, the spoon is removed and the pot is put on the fire. No stirring is done beyond this point, as it would dissolve the foam. Just as the coffee begins boiling, the pot is removed from the fire and the coffee is poured into the cups.

In Egypt, answering that you'd like it "sade" (ساده plain; no sugar, a loanword from Turkish/Persian) is completely fine, as it is interesting to also note that "sade" is the only kind of coffee allowed for mourning people who abstain from "pleasurable" sweetness).

A well-prepared Turkish coffee has a thick foam at the top (köpük in Turkish), is homogeneous, and does not contain noticeable particles in the foam or the liquid. This can be achieved only if cold water and a low heat are used. Starting with warm water or a strong heat does not leave enough time for either the coffee to sink or the foam to form. It is possible to wait an additional twenty seconds past boiling, which makes a homogeneous and delicious coffee, but the foam is completely lost. To overcome this, foam can be removed and put into cups earlier and the rest can be left to boil. In this case special attention must be paid to transfer only the foam and not the suspended particles.

There are other schools of preparing Turkish coffee that vary from the above. One such method involves starting with hot water alone, then adding and dissolving the sugar. The product is in essence a sugar syrup with a higher boiling point than water. The coffee and cardamom are added, and the mixture is stirred. It is then brought to a boil and just before serving is removed from the heat for a few seconds and returned to it, being brought to a brief boil a second time. This double (and sometimes triple) boiling is an essential part of the process, both ceremonially and — as connoisseurs claim — for the palate.

A common variation in the Arab world is allowing the brew to boil, the pot removed from the heat source just before it boils over, allowing it to settle, and then repeating the process two or three times. This results in even stronger and more concentrated coffee.

title: Cookbook:Turkish Coffee


text:
Prealgebra for Two-Year Colleges/Appendix (procedures)/Finding equivalent fractions

Equivalent fractions represent the same number, although they are written differently. For example,
 * $$\frac{1}{2}$$ and $$\frac{2}{4}$$

represent the same amount.

You can find and equivalent fraction by multiplying the numerator and denominator by the same number. For example,
 * $$\frac{1}{2} = \frac{1 {\color{Red} \times 2}}{2 {\color{Red} \times 2}} = \frac{2}{4}$$

and
 * $$\frac{1}{2} = \frac{1 {\color{Red} \times 3}}{2 {\color{Red} \times 3}} = \frac{3}{6}$$

and
 * $$\frac{1}{2} = \frac{1 {\color{Red} \times 4}}{2 {\color{Red} \times 4}} = \frac{4}{8}.$$

When you are adding fractions or subtracting fractions, you will want to find an equivalent fraction with a certain denominator. For example,
 * $$\frac{3}{5} = \frac{\color{Blue}\mathrm{?}}{45}$$

In this case, you can see that you need to multiply the numerator and denominator by 9, because 45 divided by 5 is 9. So
 * $$\frac{3}{5} = \frac{3{\color{Red}\times9}}{5{\color{Red}\times9}} = \frac{\color{Blue}27}{45}.$$

You are also allowed to divide the numerator and denominator by the same number. We usually call this reducing fractions.


text:
Wikijunior talk:Introduction to Mathematics

"This book is designed to teach you, in less than a year, all of the mathematics you need to go to college." Isn't that a rather lofty goal for a single book? I think whatever plans there are for this need to be seriously rethought. – Mike.lifeguard  | talk 20:00, 17 March 2008 (UTC)
 * I was about to write the same thing. Kayau (talk | email | contribs) 12:13, 26 September 2010 (UTC)

Splitting Page
I split the page into chapters because if the goal is to teach everything you need to know about math it's probably going to be too long for one page. Xxagile (talk) 02:20, 19 September 2008 (UTC)

Merge Wikijunior:More on Mathematicswith this page
See my rationale at Wikijunior talk:More on Mathematics. Liam987 (t) 16:24, 27 March 2015 (UTC)


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Come introduce yourself at the new users page. If you have any questions, you can ask there or contact me personally.--Webaware talk 23:07, 17 March 2008 (UTC)

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text:
Outdoor Education

Table of contents
Feel free to add extra chapters (or headings within chapters) which you would like to read or contribute to. All ideas are welcome, although they will get restructured as the book develops:

 * 1) Definition and scope
 * 2) History
 * 3) Around the world
 * 4) /Environment/
 * 5) /Experiential learning/
 * 6) /Groups and leadership/
 * 7) /Facilitation techniques/
 * 8) /Risk and safety/

How to help

 * Create a user account (top right).
 * Be bold  and start fleshing out possible content on the book's main page, or create sub-pages for specific content.
 * Add any discussion, ideas, questions, etc. to the book's discussion page (by editing it - top middle)
 * If you want to learn wiki then try help.
 * If you are teaching an outdoor education unit to trainees, this book could really do with some student-authored content being posted here! Contact Jtneill if you want a hand to set up such a learning/assessment exercise.

Subpages

 * Contributors
 * Proposal
 * Wishlist

title: Outdoor Education


text: User:Kiyura~enwikibooks

title: User:Kiyura~enwikibooks


text:
Prealgebra for Two-Year Colleges/Workbook AIE/Measuring distances

Measuring Distances

Materials Needed: Ruler marked in inches and cm, string, scissors to cut the string

Why
When you are given a map, blueprint, or diagram, you often need to measure with a ruler to get the information you need to solve the problem.

Learning Objectives

 * 1) Use a ruler to measure perimeters (whole numbers of inches and cm).
 * 2) Use a string and a ruler to measure paths that are not straight (whole numbers of inches).

Warm-up

 * 1. Explain how to calculate the perimeter of an object.

 * Add up the lengths of all the sides.

 * 2. Which of the following objects can be used to help you measure perimeter? How?

 * Measuring cup
 * Graph paper
 * Ruler
 * 3”×5” index card
 * String
 * Sand

Activity

 * 1. Without measuring, decide which of the following shapes has the larger perimeter. Explain your reasoning.

 * [[File:Rectangle white.png]] [[File:Right polygon.png]]

 * 2. Use a ruler to measure the perimeter of the rectangle in inches.

 * 3. Use a ruler to measure the perimeter of the “H” figure in centimeters.

 * 4. Use a ruler to measure the perimeter of the triangle in inches.

 * 5. Use a piece of string and a ruler to measure the perimeter of the oval in inches.

 * 6. Use a piece of string and a ruler to measure the length of the curved path in inches.

 * 7. Use a piece of string and a ruler to measure the shortest path on the map along the highways from the bull’s eye in Antioch to the bull’s eye in Oakland in inches.

 * 4 inches, to the nearest whole inch

 * 8. If each inch on the map represents 10 miles in real life, then how far is it between the spots represented by the bull’s eyes?

 * 40 miles


text:
Prealgebra for Two-Year Colleges/Workbook AIE/Length, area, and volume

Length, Weight, and Volume

Materials Needed: Textbook

Why
Real-world problems almost always contain units. Some of the most common units in the U.S. are English units of length, weight, and volume.

Learning Objectives

 * 1) Explain the difference between length, weight, and volume, and identify appropriate English units for each.
 * 2) Know the conversion factors for common English units of length, weight, and volume.
 * 3) Give examples of situations in which a given operation (+, –, , ) is appropriate.

Warm-up
You should have the following facts memorized. Complete the table. Length	: ___12__ in = 1 ft ___3__ ft = 1 yd ___5280__ ft = 1 mi		Weight	: ___16__ oz = 1 lb ___2000__ lbs = 1 ton	Time: ___60__ sec = 1 min ___60__ min = 1 hr ___24__ hr = 1 day ___30__ dys = 1 mon ___12__ mon = 1 yr ___52__ wks = 1 yr ___365__ dys = 1 yr		Volume/Capacity	: ___8__ fl oz = 1 cup ___2__ cups = 1 pt ___2__ pt = 1 qt ___4__ qt = 1 gal

Activity
1)	Does the situation describe a length, weight, or volume? Write L, W, or V. a)	Filling you car with gasV		b)	Going on a dietW			c)	Measuring cough syrupV d)	Figuring postageW		e)	Driving to CincinnatiL		f)	Building a fenceL	2)	Write an appropriate English unit for measuring each of the following: a)	The distance from San Francisco to Washington, D.C. miles b)	The weight of an aircraft carrier tons c)	The size of a soda bottle quart d)	The size of a sheet of paper inches e)	The amount of flour in a loaf of bread cup f)	The amount of Cheerios in a box oz 3)	Because of construction CalTrans needs to install 100 yds of concrete barriers along the edge of Highway 4. Each barrier is 1 yd 2 ft long. How many barriers are needed? 100 yds = 300 ft; 1 yd 2 ft = 5 ft 100/5 = 20 barriers

4)	Write a realistic problem situation for 2 tons 850 lbs – 1 ton 1430 lbs. Solve the problem you wrote. A fully-loaded pickup truck weighs 2 tons 850 lbs. If the emptied truck weighs 1 ton 1420 lbs (a fact I found in the owner’s manual), then how much does the cargo weigh? 2 tons 850 lbs – 1 ton 1430 lbs = 1420 lbs

5)	Write a realistic problem situation for 1 cup 4 fl oz  13. Solve the problem you wrote. I have 13 friends coming over on a hot day. I want to make enough lemonade to be able to serve each of them 1 cup 4 fl oz. How much lemonade do I need to make? 1 cup 8 fl oz  13 = 13 cups 52 fl oz = 19 cups 4 fl oz

6)	Write a realistic problem situation for 3 lbs 12 oz  12. Solve the problem you wrote. At Costco, a box of 12 cans of cat food weighs 3 lbs 12 oz. How much does each can weigh? 3 lbs 12 oz  12 = 5 oz

7)	Write a realistic problem situation for 24 ft 9 in + 18 ft 6 in + 24 ft 9 in + 18 ft 6 in. Solve the problem you wrote. I have a garden that is 24 ft 9 in long and 18 ft 6 in wide. What length of fencing material should I buy if I want the fence to go all the way around the garden? 24 ft 9 in + 18 ft 6 in + 24 ft 9 in + 18 ft 6 in = 84 ft 30 in = 86 ft 6 in


text: User talk:220.225.32.91

title: User talk:220.225.32.91


text:
User talk:Mav~enwikibooks

Hello I am new reader of world history. i wanted to know if any body knows about any comprehensive book about world history. Some one has proposed me the BOOK HUMAN HERITAGE Teacher version, i found it quite interesting but still i want comments and views of other readers. If some one can forward the e - version of the world history, it will be a favour. regards[[Media:Example.ogg]]

Your account will be renamed
Hello,

The developer team at Wikimedia is making some changes to how accounts work, as part of our on-going efforts to provide new and better tools for our users like cross-wiki notifications. These changes will mean you have the same account name everywhere. This will let us give you new features that will help you edit and discuss better, and allow more flexible user permissions for tools. One of the side-effects of this is that user accounts will now have to be unique across all 900 Wikimedia wikis. See the announcement for more information.

Unfortunately, your account clashes with another account also called Mav. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name Mav~enwikibooks that only you will have. If you like it, you don't have to do anything. If you do not like it, you can pick out a different name.

Your account will still work as before, and you will be credited for all your edits made so far, but you will have to use the new account name when you log in.

Sorry for the inconvenience.

Yours, Keegan Peterzell Community Liaison, Wikimedia Foundation 23:26, 17 March 2015 (UTC)

Renamed
 This account has been renamed as part of single-user login finalisation. If you own this account you can |log in using your previous username and password for more information. If you do not like this account's new name, you can choose your own using this form after logging in: . -- Keegan (WMF) (talk) 05:14, 19 April 2015 (UTC)

title: User talk:Mav~enwikibooks


text:
User:Jtneill

James Neill is a lecturer in psychology at the University of Canberra.

I'm contributing to

 * Motivation and emotion
 * Outdoor Education
 * Research Methods
 * Introduction to Psychology <-> Psychology
 * Social Psychology
 * Statistics

I'm reading

 * Exercise as it relates to Disease
 * Contemporary Educational Psychology
 * Foundations of Education and Instructional Assessment
 * Adventist Youth Honors Answer Book
 * First Aid
 * FOSS A General Introduction
 * Handbook of Management Scales
 * Learning Theories
 * MediaWiki Administrator's Handbook
 * Principles of Sociology
 * Social and Cultural Foundations of American Education
 * US History
 * Naming policy

I'm learning about

 * Help:Revision review
 * Development stages
 * Manual of Style
 * User:Whiteknight/New Book Guide
 * Media

People helping me to learn about wikibooks

 * Mike.lifeguard

Good design

 * Manual of Style
 * Naming policy
 * French/Grammar/Tenses

title: User:Jtneill


text:
AQA Information and Communication Technology/ICT5/Human-Computer Interaction

Human-Computer interaction is concerned with the design, evaluation and implementation of interactive computer systems, using Human-Computer interfaces in the safest and most healthy way.

Ergonomics
Ergonomics are the designs and functionality of the environment. Applying this would be a study of the environment to see how improvement can be made more comfortable for the users.

Measures to improve the ergonomics include

 * Improved lighting
 * Furniture better suited

Why is this important?

 * Could improve productivity
 * Prevent RSI (Repetitive Strain Injury).
 * With adjustable chairs and furniture in the right positions, could be prevented.
 * Energy Efficiency
 * Improve Job satisfaction (motivates)

Psychological Factors
The understanding of how users receive, process and store information.

Information can be received by 4 main ways:
 * Vision (seeing)
 * Distinguishing colours can effect how a person reacts to a situation (Red means Warning or Danger). This shouldn't be relied on because of colour blindness.
 * Hearing
 * Most commonly sounds are used in warning messages - the Dong in Windows. This is standard and therefore the user knows straight away that it is a warning.
 * Touch
 * Human nature wants something to ensure a button has been pressed - buttons allow that pressure to be enforced.
 * Movement
 * The movement of small objects is understandably difficult.


text:
AQA Business Studies

Marketing

 * /Elasticity of Demand/
 * /Marketing Mix/

Finance

 * /Uses and Limitations of Accounts/
 * /Ratio Analysis/
 * /Revenue and Capital Expenditure/
 * /Budgeting/
 * /Cash Flow Management/

Ownership and Objectives

 * /Changes in Ownership/

External Influences

 * /Economic Growth/
 * /Social Responsibilities/

title: AQA Business Studies


text:
Talk:How to Drive in California, USA/Four-way stops

Well isn't this spiffy. Someone has renamed the chapters and has done away with the link at the bottom that wouild allow the reader to progress through the book (the main thing I am after after they decide to read this guide)

What the Hell?

Beamer--Beamer (talk) 11:56, 18 March 2008 (UTC)

So all the work I did on this page in the history is now gone?

Excellent.--Beamer (talk) 12:03, 18 March 2008 (UTC)

You know what this place ought to be called is feel free to come here and write a fing book, but be prepared to have it twisted and stomped on so you have no say in how it progresses. I really feel right now like dropping the whole damn thing. Thanks ever so much.--Beamer (talk) 12:03, 18 March 2008 (UTC)


text: User talk:84.9.60.26

title: User talk:84.9.60.26


text:
QEMU/Monitor

When QEMU is running, it provides a monitor console for interacting with QEMU. Through various commands, the monitor allows you to inspect the running guest OS, change removable media and USB devices, take screenshots and audio grabs, and control various aspects of the virtual machine.

The monitor is accessed from within QEMU by holding down the Ctrl and Alt keys (or whatever the "mouse grab" keystrokes are), and pressing. Once in the monitor,  switches back to the guest OS. Typing  or   in the monitor brings up a list of all commands. Alternatively the monitor can be redirected to using the  command line option. Using  will send the monitor to the standard output, this is most useful when using qemu on the command line.

help
With no arguments, the help command lists all commands available. For more detail about another command, type help command, e.g. (qemu) help info On a small screen / VM window, the list of commands will scroll off the screen too quickly to let you read them. To scroll back and forth so that you can read the whole list, hold down the control key and press Page Up and Page Down.
 * help [command] or ? [command]

info
Show information on some aspect of the guest OS. Available options are:
 * info option
 * block – block devices such as hard drives, floppy drives, cdrom
 * blockstats – read and write statistics on block devices
 * capture – active capturing (audio grabs)
 * history – console command history
 * <tt>irq</tt> – statistics on interrupts (if compiled into QEMU)
 * <tt>jit</tt> – statistics on QEMU's Just In Time compiler
 * <tt>kqemu</tt> – whether the kqemu kernel module is being utilised
 * <tt>mem</tt> – list the active virtual memory mappings
 * <tt>mice</tt> – mouse on the guest that is receiving events
 * <tt>network</tt> – network devices and VLANs
 * <tt>pci</tt> – PCI devices being emulated
 * <tt>pcmcia</tt> – PCMCIA card devices
 * <tt>pic</tt> – state of i8259 (PIC)
 * <tt>profile</tt> – info on the internal profiler, if compiled into QEMU
 * <tt>registers</tt> – the CPU registers
 * <tt>snapshots</tt> – list the VM snapshots
 * <tt>tlb</tt> – list the TLB (Translation Lookaside Buffer), i.e. mappings between physical memory and virtual memory
 * <tt>usb</tt> – USB devices on the virtual USB hub
 * <tt>usbhost</tt> – USB devices on the host OS
 * <tt>version</tt> – QEMU version number
 * <tt>vnc</tt> – VNC information

change
The  command allows you to change removable media (like CD-ROMs), change the display options for a VNC, and change the password used on a VNC.
 * <tt>change device setting</tt>

When you need to change the disc in a CD or DVD drive, or switch between different .iso files, find the name of the CD or DVD drive using  and use   to make the change. (qemu) info block ide0-hd0: type=hd removable=0 file=/path/to/winxp.img ide0-hd1: type=hd removable=0 file=/path/to/pagefile.raw ide1-hd1: type=hd removable=0 file=/path/to/testing_data.img ide1-cd0: type=cdrom removable=1 locked=0 file=/dev/sr0 ro=1 drv=host_device floppy0: type=floppy removable=1 locked=0 [not inserted] sd0: type=floppy removable=1 locked=0 [not inserted] (qemu) change ide1-cd0 /path/to/my.iso (qemu) change ide1-cd0 /dev/sr0 host_device

eject
Use the  command to release the device or file connected to the removable media device specified. The  parameter can be used to force it if it initially refuses!
 * <tt>eject [-f] device</tt>

block_resize
Notify QEMU that a block device has been resized. $ info block drive-virtio-disk3 (#block790): /guest/mud_vdd (raw) $ block_resize drive-virtio-disk3  16G

usb_add
Add a host file as USB flash device ( you need to create in advance the host file: dd if=/dev/zero of=/tmp/disk.usb bs=1024k count=32 )

usb_add disk:/tmp/disk.usb

usb_del
use info usb to get the usb device list (qemu) info usb Device 0.1, Speed 480 Mb/s, Product XXXXXX Device 0.2, Speed 12 Mb/s, Product XXXXX

(qemu) usb_del 0.2 This deletes the device

mouse_move
Sends Mouse Movevment events to guest. mouse_move dx dy [dz] -- send mouse move events. Example: [qemu]mouse_move -20 20

sendkey keys
You can emulate keyboard events through sendkey command. The syntax is: sendkey keys. To get a list of keys, type <tt>sendkey [tab]</tt>. Examples:
 * <tt>sendkey a</tt>
 * <tt>sendkey shift-a</tt>
 * <tt>sendkey ctrl-u</tt>
 * <tt>sendkey ctrl-alt-f1</tt>

As of QEMU 0.12.5 there are:

screendump
Capture a screendump and save into a PPM image file.
 * <tt>screendump filename</tt>

wavcapture
Capture the sound of the vm and save it into a specified .wav file.
 * <tt>wavcapture filename</tt>

stopcapture
Stop recording the wavcapture. Index of the first wavcapture is 0.
 * <tt>stopcapture index</tt>

commit
When running QEMU with the  option, commit changes to the device, or all devices.
 * <tt>commit device</tt> or <tt>commit all</tt>

quit
Quit QEMU immediately.
 * <tt>quit</tt> or <tt>q</tt>

savevm
Save the virtual machine as the tag 'name'. Not all filesystems support this. raw does not, but qcow2 does.
 * <tt>savevm</tt> name

loadvm
Load the virtual machine tagged 'name'. This can also be done on the command line: <tt>-loadvm</tt> name
 * <tt>loadvm</tt> name

With the <tt>info snapshots</tt> command, you can request a list of available machines.

delvm
Remove the virtual machine tagged 'name'.

stop
Suspend execution of VM

cont
Reverse a previous stop command - resume execution of VM.

system_reset
This has an effect similar to the physical reset button on a PC. Warning: Filesystems may be left in an unclean state.

system_powerdown
This has an effect similar to the physical power button on a modern PC. The VM will get an ACPI shutdown request and usually shutdown cleanly.

log

 * <tt>log option</tt>

logfile
Write logs to specified file instead of the default path,.
 * <tt>logfile filename</tt>

gdbserver
Starts a remote debugger session for the GNU debugger (gdb). To connect to it from the host machine, run the following commands: shell$ gdb qemuKernelFile (gdb) target remote localhost:1234

x
x /format address

Displays memory at the specified virtual address using the specified format.

Refer to the xp section for details on format and address.

xp
xp /format address

Displays memory at the specified physical address using the specified format.

format: Used to specify the output format the displayed memory. The format is broken down as ''/[count][data_format][size]
 * count: number of item to display (base 10)
 * data_format: 'x' for hex, 'd' for decimal, 'u' for unsigned decimal, 'o' for octal, 'c' for char and 'i' for (disassembled) processor instructions
 * size: 'b' for 8 bits, 'h' for 16 bits, 'w' for 32 bits or 'g' for 64 bits. On x86 'h' and 'w' can select instruction disassembly code formats.

address:
 * Direct address, for example: 0x20000
 * Register, for example: $eip

Example - Display 3 instructions on an x86 processor starting at the current instruction: (qemu) xp /3i $eip

Example - Display the last 20 words on the stack for an x86 processor: (qemu) xp /20wx $esp

print
Print (or p), evaluates and prints the expression given to it. The result will be printed in hexadecimal, but decimal can also be used in the expression. If the result overflows it will wrap around. To use a the value in a CPU register use $. The name of the register should be lower case. You can see registers with the info registers command.

Example of qemu simulating an i386. (qemu) print 16 0x10 (qemu) print 16 + 0x10 0x20 (qemu) print $eax 0xc02e4000 (qemu) print $eax + 2 0xc02e4002 (qemu) print ($eax + 2) * 2 0x805c8004 (qemu) print 0x80000000 * 2 0

More information on the architecture specific register names can be found from the below qemu source file

http://git.qemu.org/?p=qemu.git;a=blob;f=monitor.c;h=1266ba06fb032cb0e7c9dbaa1b6d22cd9047c6b4;hb=HEAD#l3044

sum
Usage: sum Computes the checksum of the specified memory region

memsave
Usage: memsave

Links
Monitor in QEMU documentation: https://www.qemu.org/docs/master/system/monitor.html

title: QEMU/Monitor


text: User talk:64.53.34.60

title: User talk:64.53.34.60


text:
United Nations History/League Attacked

Overview
The League lacked its own armed force and so depended on the Great Powers to enforce its resolutions, keep to economic sanctions which the League ordered, or provide an army, when needed, for the League to use. However, they were often reluctant to do so. Benito Mussolini stated that "The League is very well when sparrows shout, but no good at all when eagles fall out."

Article X of the League of Nations (1919)
"The Members of the League undertake to respect and preserve as against external aggression the territorial integrity and existing political independence of all Members of the League. In case of any such aggression or in case of any threat or danger of such aggression the Council shall advise upon the means by which this obligation shall be fulfilled."

Because of these provisions, the United States Senate decided to not ratify the League's Charter.

Anit-Moderni
The League was attacked as being a conspiracy to bring in the One World Government, the Anti-Christ (the supposed "King of the Jews", and set up world wide Judaism. It was also claimed to be Masonic and Nihilistic.

Chaco War
The League failed to prevent the Chaco War between Bolivia and Paraguay in 1932 over the arid Gran Chaco region of South America. Although the region was sparsely populated, it gave control of the Paraguay River which would have given one of the two landlocked countries access to the Atlantic Ocean, and there was also speculation, later proved incorrect, that the Chaco would be a rich source of petroleum. Border skirmishes throughout the late 1920s culminated in an all-out war in 1932, when the Bolivian army, following the orders of President Daniel Salamanca Urey, attacked a Paraguayan garrison at Vanguardia. Paraguay appealed to the League of Nations, but the League did not take action when the Pan-American conference offered to mediate instead.

The war was a disaster for both sides, causing 100,000 casualties and bringing both countries to the brink of economic disaster. By the time a ceasefire was negotiated on 12 June 1935, Paraguay had seized control over most of the region. This was recognized in a 1938 truce by which Paraguay was awarded three-quarters of the Chaco Boreal.

title: United Nations History/League Attacked


text:
United Nations History/U Thant

Who was he?
U Thant was a Burmese diplomat and the third Secretary-General of the United Nations, from 1961 to 1971. He was chosen for the post when his predecessor Dag Hammarskjöld was killed in a plane crash in September 1961.

"U" is an honorific in Burmese, roughly equal to "Mister." "Thant" was his only name. In Burmese he was known as Pantanaw U Thant, a reference to his home town of Pantanaw.

Secretary General
Thant began serving as Acting Secretary-General from November 3, 1961, when he was unanimously appointed by the General Assembly, on the recommendation of the Security Council, to fill the unexpired term of Dag Hammarskjöld. He was then unanimously appointed Secretary-General by the General Assembly on November 30, 1962 for a term of office ending on November 3, 1966. During this first term he was widely credited for his role in defusing the Cuban Missile Crisis and for ending the civil war in the Congo.

U Thant was re-appointed for a second term as Secretary-General of the United Nations by the General Assembly on December 2, 1966 on the unanimous recommendation of the Security Council. His term of office continued until December 31, 1971, when he retired. During his time in office, he oversaw the entry into the UN of dozens of new Asian and African states and was a firm opponent of apartheid in South Africa. He also established many of the UN's development and environmental agencies, funds and programmes, including the UN Development Programme (UNDP), the UN University, UNCTAD, UNITAR and the UN Environmental Programme.

Mediation
He had also led many successful though now largely forgotten mediation efforts, for example in Yemen in 1962 and Bahrain in 1968. In each case, war would have provoked a wider regional conflict, and it was Thant's quiet mediation which prevented war.

Opposition to Vietnam
He is also famous for opposing the United States for its Vietnam War.

title: United Nations History/U Thant


text:
United Nations History/Kurt Waldheim

Who was he?
Kurt Josef Waldheim (21 December 1918 – 14 June 2007) was an Austrian diplomat and politician. Waldheim was Secretary-General of the United Nations from 1972 to 1981, and President of Austria from 1986 to 1992. While running for President in Austria in 1985, his service as a Wehrmacht intelligence officer during World War II raised international controversy.

Service in World War II
In early 1941 Waldheim was drafted into the Wehrmacht and sent to the Eastern Front where he served as a squad leader. In December 1941 he was wounded but returned to service later on. His further service in the Wehrmacht from 1942 to 1945 (at age 24 to 27) was subject of the international dispute regarding his person in 1985 and 1986. In 1985, in his autobiography, he stated that he was discharged from further service at the front and for the rest of the war years finished his law degree at the University of Vienna and married in 1944. Later documents and witnesses would come to light revealing that Waldheim’s military service continued until 1945, while it is correct that he graduated from the University of Vienna in 1945 receiving a law degree and that he married in 1944.

As Secretary General
After being defeated in his home country's presidential election, he was elected to succeed U Thant as United Nations Secretary-General the same year. As Secretary-General, Waldheim opened and addressed a number of major international conferences convened under United Nations auspices. These included the third session of the United Nations Conference on Trade and Development (Santiago, April 1972), the United Nations Conference on the Human Environment (Stockholm, June 1972), the Third United Nations Conference on the Law of the Seas (Caracas, June 1974), the World Population Conference (Bucharest, August 1974) and the World Food Conference (Rome, November 1974). However, his diplomatic efforts particularly in the Middle East were over shadowed by the diplomacy of then US Secretary of State, Henry Kissinger. In a 1976 security council debate he described the Israeli rescue of hijacked airline passengers at Entebbe, Uganda as "a serious violation of the national sovereignty of a United Nations member state."

Waldheim was re-elected in 1976 despite some opposition. Waldheim and then-U.S. President Jimmy Carter both prepared written statements for inclusion on the Voyager Golden Records, now in deep space. In 1980 Waldheim flew to Iran in an attempt to negotiate the release of the American hostages held in Tehran, but Ayatollah Khomeini refused to see him. While in Tehran, it was announced that an attempt on Waldheim's life had been foiled. Near the end of his tenure as Secretary-General, Waldheim and Paul McCartney also organized a series of concerts for the People of Kampuchea to help Cambodia recover from the damage done by Pol Pot.

When Waldheim sought a third Secretary-General term, the People's Republic of China used their veto powers to block this development. He was succeeded by Javier Pérez de Cuéllar of Peru.

Ostrovsky claims
In 1994 the former Mossad officer Victor Ostrovsky claimed in his book The Other Side of Deception that Mossad doctored the file of the then UN Secretary General to implicate him in Nazi crimes. These allegedly false documents were subsequently "discovered" by Benjamin Netanyahu in the UN file, and triggered the "Waldheim Affair". Ostrovsky says the reason was Waldheim's criticism of Israeli action in Lebanon. Controversy surrounds Ostrovsky and his writings and the veracity of his writings is widely disputed, with some intelligence experts arguing The Other Side of Deception should be viewed as a novel rather than a work of non-fiction.

title: United Nations History/Kurt Waldheim


text:
United Nations History/Javier Pérez de Cuéllar

Who Was he?
Javier Michael Pérez de Cuéllar Mahan (born January 19, 1920, in Lima) is a Peruvian diplomat who served as the fifth Secretary-General of the United Nations from January 1, 1982 to December 31, 1991. He studied in Colegio San Agustín of Lima, and then at Pontificia Universidad Católica del Perú. In 1995, he ran unsuccessfully against Alberto Fujimori for President of Peru. He was President of the Council of Ministers, as well as Minister of Foreign Affairs from November 2000 until July 2001, during the turbulent period following Fujimori's resignation over corruption charges. In September 2004, he stepped down from his position as Peru's Ambassador to France, where he formerly resided. With the death of Kurt Waldheim in June 2007, he became the oldest former Secretary General of the United Nations.

Doctorate Degrees
Mr. Perez de Cuellar received doctorate degrees honoris causa from the following universities: the University of Nice; the Jagiellonian University at Cracow; Charles University at Prague; the University of Sofia; the University of San Marcos at Lima; the Free University at Brussels; Carleton University at Ottawa, Canada; the University of Paris (Sorbonne); the University of Visva-Bharati in West Bengal, India; the University of Michigan; the University of Osnabruck in the Federal Republic of Germany; the Coimbra University at Coimbra, Portugal; the Mongolian State University at Ulan Bator; the Humboldt University of Berlin; the Moscow State University; the University of Malta in Valleta; the Leyden University in the Netherlands; La Salle University in Philadelphia; Tufts University in Medford, Massachusetts; the Johns Hopkins University in Baltimore, Maryland; and Cambridge University in the United Kingdom.

Diplomatic Career
Pérez de Cuéllar joined the Ministry of Foreign Affairs in 1940 and the diplomatic service in 1944, serving subsequently as Secretary at Peru's embassies in France, where he met and married his first wife, the former Yvette Roberts; the United Kingdom, Bolivia, and Brazil. He later served as ambassador to Switzerland, the Soviet Union, (concurrently in Poland), and Venezuela. From his first marriage, Mr. Perez de Cuellar has a son, (Francisco, b. Paris), and a daughter, Agueda Cristina (b. London).

He was a junior member of the Peruvian delegation to the General Assembly at its first session - held in London in 1946-, and a member of the delegations to the 25th through 30th sessions of the Assembly. In 1971, he was appointed permanent representative of Peru to the United Nations, and he led his country's delegation to all sessions of the Assembly from then until 1975.

In 1973 and 1974, he represented his country in the Security Council, serving as its President at the time of the events in Cyprus in July 1974. On 18 September 1975, he was appointed Special Representative of the Secretary-General in Cyprus – a post he held until December 1977-, when he rejoined the Peruvian Foreign Service. During his time in Cyprus, Mr. Perez de Cuellar married his current wife, the former Marcela Temple Seminario, with whom he has no children.

As Secretary General
On December 31, 1981, Pérez de Cuéllar succeeded Kurt Waldheim as Secretary-General and was re-elected for a second term in October 1986. During his two terms, he led mediations between Britain and Argentina in the aftermath of the Falklands War and promoted the efforts of the Contadora Group to bring peace and stability to Central America. He also interceded in the negotiations for the independence of Namibia, the conflict in Western Sahara between Morocco and the Polisario Front, and the Cyprus issue. Shortly before the end of his second term, he was unofficially requested by members of the Security Council to reconsider his earlier decision not to run for a third term, albeit shortened to two years, as a search for his successor had not, as of then, yielded a consensus candidate. Mr. Pérez de Cuéllar graciously[citation needed] declined the offer once a candidate was found, in late December 1991, his second term as Secretary-General concluding, as scheduled, on December 31, 1991.