Unit Operations

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 http://scienceblogs.com/startswithabang/2012/10/10/hey-physics-astronomy-professors-this-is-not-okay/

The one lasting regret of my life is that I had to learn with great difficulty and unlearn and relearn what were called Units & Dimensions.

It all started when I was 5 and Father tried teaching me how to tell time on our grandfather-clock...the Galileo's original pendulum...hanging on our wall. It was a mystery to me since I learned counting up to 100 and I was told that the greatest invention of mankind and Indiankind is the invention of the zero and the decimal system. There was no reason why the day should be split into a dozen hours and so also the night. Why not 10? Or 100?

And that every hour is divided into all of 60 minutes and every minute into 60 seconds. I asked Father why and he kept quiet...maybe he banged me: "Don't ask...just listen!"

I came to know later on that the entire mischief stemmed from the Egyptians (or Greeks?) who fancied that it would be nice if the heavens could be split up into 12 zodiacal signs. If you had ever looked at these so-called signs like the Leo or the Virgo, not to speak of the huge Scorpio, you will see it is utter nonsense...they are all of different sizes and some of them don't resemble anything at all except for fevered imaginations...like say Cancer (I hope I don't get it soon). There could as well have been 50 zodiacal signs named 1, 2, 3...50. And the day could have been divided into a neat 100 hours and so on...no more dozens.

Talking of dozens there is this squeamish baker's dozen (13). When I went to Vizagh, I was duped by the fruit-sellers and flower-sellers into believing that 100 is a hundred. I came to know from cognoscenti later on that, in the Poorna Market, 100 means 115 and 120 if you can drive a hard bargain. 

And then came this mile. We had to mug up that a mile has 8 (?) furlongs and a furlong had 220 (!) yards, a yard has 3 (?) feet and each foot has 12 (again) inches. And I had to mug up things called acres, links and hectares for square things. 

I am told that the Americans in their pigheadeness still stick to miles. Otherwise they were so nice to divide their dollar into 100 cents. Unlike the Brits who stuck to pounds (sterling, not to be confused with avoirdupois) and all those shillings and pence which we had to mug up...also guinea (pig?), crown, farthing and what not. And ours was no better...we had a rupee that was divided into 16 (?) annas. Each anna had four chinna dabbulu. Each chinna dabbu had 3 (?) dammidis. There was a pedda dabbu which was neither here nor there...it had all of 4 dammidis.

I don't know how I survived manipulating all these queer figures...totally unnecessary. 

I then went to the University to do physics (unfortunately) and had to master what were called 1. the fps system, 2. the cgs system, 3. the MKS system and 4. the SI system. In addition, there were the engineering units like the BTU, pounds and poundals and slugs (serves them right). 

And in my third year we had the horrible subject called Electricity and Magnetism. Fortunately by then we could forget the fps business but had to learn two types of cgs (the esu and emu) and the conversion between them...involving only powers of 3 and 10...someone thought that the speed of light was 3 x (10 ^10) somethings.  

Incidentally, I just now typed (by mistake) in Google:

"Speed of light in seconds per cm"

And got this leading boxed-in figure:

the speed of light =

3.33564095 × 10^-11 seconds per centimeter

Just another instance of the IBM 1620 Law:

"Input bullshit...output bullshit"

Just when I was about to rejoice, they threw in the Gaussian, the Lorentzian and the Heaviside units (rationalized as well as non-rationalized).

And our books (British pigheadedness this time) had the first chapter on what was called the Units & Dimensions. All in all the British (unlike the Americans like Sears and Feynman) tried their best to make physics as repulsive as possible.

Fortunately by the time I went to IIT KGP to teach physics to unwilling students, things fell into place and we had but to mug up only the SI units, still a pain in the neck since they tried to name the units (as far as they could) in terms of the great physicists like Newton and Faraday...also less know chaps like Tesla and Weber...there must have been terrific fights. I would like to see a unit named 'Feynman' who single-handedly tried to make physics attractive to students. I propose to name the speed of light after Feynman and the gravitational constant after Einstein.

But I had to teach half a semester course on Dimensional Analysis to Engineering students. And I came to love the subject. I found good books by Bridgman and others. And it was a revelation. It had the Buckingham Pi Theorem. Earlier I thought it was a boring subject dealing with 3 dimensions...mass, length, time.

For the first time I learned the importance of dimensionless products like the Reynold's Number. And the subject was of great practical interest in modeling (ahem!). Let us say a civil engineer has to design a bridge over the Hooghly river. He can't do it on the real river...it would collapse and he has to do it all over again. So, he would make a miniature model of the damn thing in say araldite. To reduce the real bridge to the lab model, he has to know by how many factors each parameter like the height, the width, the number and size of the piers etc had to be reduced. And what properties like the density and the elasticity of araldite differ from the ultimate steel bridge. It is not easy. There are too many parameters and only 3 dimensions. So he has to use his horse sense to reduce them into dimensionless products. And test the thing using a tough subject called Photoelastcity that requires a knowledge of polarization of light.

And I learned a lot and it was fun to teach.

And then I made friends with a Chemical Engineer who was all the time talking of Unit Operations. I asked him what they were. And he reeled out:

1. Mass Transfer

2. Heat Transfer

3. Momentum Transfer.

I then told him that I read all of them in my Second Year B Sc (Hons) in the Kinetic Theory. They were called Diffusion, Conduction, and Viscosity and were dismissed in 6 pages.

He then took me to the Central Library and showed me three full racks of books on these three subjects in the Ch E Section!

Somehow it stuck. 

Nowadays every morning I recall the 3 Unit Operations I have to perform grudgingly. They are called:

1. Shit

2. Shave

3. Shampoo.

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Multiple Choice - My Foot!

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 http://www.savagechickens.com/2009/04/multiple-choice.html 

Somehow I never liked 'multiple choice' questions like the above in which more than one answer is correct. The reason is not that physics is an exact science...rather that it is an approximate science. Since all the things we 'ignore' can't be specified in a question, the 'right' answer often boils down to semantics. 

Take this simple problem of projectiles: A cricket ball is bowled at such and such a speed at such and such a height at such and such an angle and you have to find where it hits the ground. The right answer in the 'model sheet' is, say, 20 yards. In truth it can be anywhere between 10 and 20 if you take the air friction, wind speed, spin of the earth, size of the ball, seam, swing...etc etc.

I was admitted to our High School in the lowest form, the 1st, in 1951. Our Board didn't recognize the marks awarded by our local elementary schools and so all of us, young and old, had to appear in an Entrance Exam and pass it. The question paper only had some questions in Telugu and a few on arithmetic (only addition and subtraction). 

I passed, somehow.

Two years later, Father (the HM) suggested to our math teacher to give some choice in his question paper at the entry level. And there was this Sivaram, the youngest son of our Telugu Pundit. Father showed me his answer script with bouts and bursts of laughter, saying he didn't know how to pass this kid...which he should...otherwise the Telugu Pundit would fail me in my next exam.

There was this question: "Answer any problem you like" with four choices. And all the choices had wicked subtractions involving 'borrow and carry' or whatever. So this whizkid gave this answer: (9999-8888=1111). Which was perfectly right but was not one of the choices given. I then carefully read the question paper, which was perhaps set in a hurry, and pointed out that the paper-setter forgot to mention: "among the following" after "any problem you like". Father heaved a sigh of relief and gave the kid full marks and he was in.

It was only in our 5th form that a newfangled thing called the 'bit paper' was invented in our science exam. This had a pull-out sheet of 40 marks that had 20 objective questions, each with only one correct answer to be checked among the 4: "A, B, C, or D". And our teachers loved it. Because, they could outsource the lousy job of evaluating the bit papers to their wives, aunts, and widowed mom-in-laws...it needed no knowledge of science. 

A couple of years later, they introduced what was called 'negative marking'...+2 for the right answer and -1 for the wrong; and the household ladies refused to do the job of evaluating the screwed up bit paper...it got too complicated for them.

We had no objective questions at our University. They were all essay questions. But there was ample choice: "Answer any 5 out of the following 8 questions. All questions carry equal marks". This was great for us. We could skip reading Geometrical Optics in the Optics paper, Sound in "Mechanics, Heat and Sound" and the treacherous Inorganic Chemistry in Chemistry.

When I went as a teacher of Physics to IIT KGP, I followed our  University system of asking students to answer any 5 out of 8. Several teachers did the same but a few inserted the caveat: "Answers to a question should all be at the same place. And questions should be attempted serially" (inter alia).

The problem was that some students would attempt more than 5 questions and at random places...half here, one-fourth on page 6 etc. And the teacher would have to collect all of the bits and pieces and decide which answer had to be discarded...some said, the last question attempted, while others said the one with the lowest mark...it was hell all in all.

And then there was this instance when I was the Chief Invigilator in a big hall. And one of the question papers (not mine) was on an elective in physics. And it was a 3-hour exam. But all the dozen or so students submitted their answer scripts a minute after the mandatory half-hour and ran away...they said the paper was too easy. The invigilators from other departments were laughing at physics about it.

So, to avoid all these troubles, I invented my own gimmick. Suppose the paper was out of 100 for 3 hours. I would give a dozen questions showing marks against each question. If you add up all the marks, it would come to 150 say. And the instruction to the student ran:

"Answer as many questions as you can, in any order you like. The cut-off mark is 100"

So if anyone got say 130, his extra 30 would just be discarded in the bin. And since the students at IIT KGP were greedy, they would attempt all questions which would pin them down for all of 3 hours.

But in the First Year Jumbo class I gave them an incentive in the midsem exam. The paper was out of 35. And the cut-off was at 30. I announced beforehand that I would read out in the vast class room the names of the few students who get more than 30. The extra marks wouldn't get added up anywhere, but the reading out of the names of the 'geniuses' was fun and they looked forward to it. 

Once I did this bit of horsing around, best described by one of the toppers in ECE of the 2002 class:

"...Once in class, when someone asked you about grades, you had said something to the effect that "those scoring over 25 will qualify for an Ex, and if you score over 30, then I will recommend to the dean that your branch be changed to Physics". In the pin drop silence that suddenly enveloped the class, you laughed and said "Don't worry. I know Physics is for people who don't score top marks in their exams", or something to that effect. There was palpable relief in the room, along with loud laughter.."

...Aniket Aga

But indeed there was this kid from the 2004 Jumbo class. He got all the 35 out of 30 and there was tremendous clapping when I read out his name. He topped in the endsem too. At the end of the semester, he approached me and said he would love to change over from ECE to Physics! And, as usual, I dissuaded him...and left KGP soon after in 2005.

I came to know recently that he did cross over to physics after his B. Tech, in spite of me. And he is now in the Physics Department of the University of Wisconsin-Madison:

http://scholar.google.co.in/citations?user=2aPCX48AAAAJ&hl=en

His name is Sourabh Maiti...
 


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