Mustard Seeds

This is a simple packet of mustard seeds. Do you notice that some of the seeds are clinging the side of the packet? Simply open and pour a packet of Mustard seeds and then you will see this happening.

Why are these seeds hanging around!? What stops them from falling to the bottom like the rest of the seeds? What gives them repulsive force to oppose the force of gravity?
It doesn't happen like this, for example, for a salt or a sugar packet.

In case of mustard seeds, what is happening is, the seeds are getting charged up, and the charge stays on them for a while, after which they become neutral. The charging is due to stripping off of an electron or two from the lattice of the mustard seed.

Can you estimate how much is the force generated because of charges separated in the case of mustard seeds shown in packet?

Assume that two seeds are 1 cm apart, and 1 seed's force on the other is balancing its weight.

mg=k(q^2)/(r^2)

m= mass = density * volume = 0.426902 gm/cm^3 * volume from this link.

g= 980 cm/s^2

k= 1 in case of CGS units

q= charge to be found out

r=1cm

Rad= radius or mustard seed = 1 mm say = 0.1 cm

hence q^2= density*volume*g* r^2

hence q= sqrt(0.426902 * (4/3)*3.14 * 10^(-3) * 980 * 1^2)

= 1.132346 statCoulomb

and using 1 StatCoulomb = 0.1 Am/c ≈ 3.3364×10¹⁰ C

and charge on one electron , e = 1.6 * 10 ^ (-19) C, we get

q = 1.132346 * 3.3364 * (10 ^ 10 ) C = 3.77796e+10 C which is a huge charge! so the mustard seeds are not hanging on the sides because of repulsive forces. They are sharing particular positions on the plastic cover. What must be happening is that the electrons are stripped off the mustard seed, and deposited on the plastic cover. The same equation with r = 1 0 Angstrom (Typical lattice planes separation distances are in this range, e.g. from this ref.) then becomes

r= 10 Angstrom = 10 * 10^(-10) m = 10 * 10 ^ (-8) cm = 10^(-7) cm

q = sqrt ( 0.426902 * (4/3)*3.14 * 10^(-3) * 980 * 10^(-14) )

= 1.32 * 10 ^(-7) stat coulomb

= 1.32 * 10 ^(-7)* 3.3364 * (10 ^ 10 ) C

= 4415 C= 3806 * 10^19 e

which is also huge.

So what must be happening is, even at smaller level, say 1 Angstrom , the electrons are stripped off and deposited to the plastic cover. Then some kind of temporary chemical bondings must be happening, since we approach molecular distances at that level.

Notice how in this simple physical situation in front, we could calculate and figure out what's happening in there. Thus physics helps you to be a Sherlock Holmes in the nature's mysterious ways of functioning!

Electrostatics Lab demo

for Engineers wanting to pursue PhD

There are number of queries of Engineers {Who probably got strayed into tech biz but had a inner longing to do Physics!:) } who would like to pursue a research Career, so this blog.

You are most welcome to do a PhD in Astronomy and Astrophysics. Visit IIA website for details of application procedure, exams and interviews to be taken. PhD in Computation or Instrumentation or Electronics based experimentation, Observational Astronomy would be possible.

Not much prior knowledge of Astronomy is expected as you will be given good grinding in Research Training Program (RTP) in the first year of joining. {You need to clear it well to get into second year!}

Many institutes have their own entrance tests and interviews. Check their websites and call their offices.

You can prepare for JEST and/or NET Physics and/or GATE Physics as follows:-

0.Check their syllabus

1. Brush up your FE Fundamentals of Physics book

2. Refer

*Fundamentals of Physics by Resnik and Halliday.

*Concepts of Modern Physics by Arthur Beiser.

*Electrodynamics by Griffith

3. Catch up with some sample papers from the same agency where you apply for these exams

4. Solve loads of problems. You Cant Survive In Research if you don't like to solve problems. Only understanding Stuff is not enough... :) ''Physics by Example'' by Rees is a good start. Actually, any good problem solving book with detailed solutions is good enough. Check solution after you have attempted the problem, and see where you made mistake, if any.

This is not necessarily the most complete and sufficient prep! Apply for a YES!+ also... check www.yesplus.org

All the best!

The younger Twin

Thanks to Amrita for asking this question about Twin Paradox. It was a thoughtful question, and the right questions at right time can lead to Big progress and good understanding. I have quoted below this dialog as it is. It reminds me of one story from Puranas, which indicates that the superfast(close to c) time travel could have been possible earlier.

The story goes like this:-

There was a King and he had a pretty daughter. He couldn't find a suitable groom for his pretty daughter, and so he set himself and her on a travel to Brahmaloka. When he reached Brahmaloka, Brahma gave him blessing and asked him to marry her to the King of a certain country on Earth. Happy, the King traveled back to the Earth with his daughter. Coming to the earth, he was so surprised that his city, his buildings and people were not there at all. In his City, he himself and all the human beings were as tall as a coconut tree. And he was shocked to see the human beings in the size of 5-6 feet, so small compared to him and her daughter. Upon inquiry, the King got to know that their civilization used to exist several thousand centuries ago! Though the King and his daughter had only aged by an year or so, the time had elapsed much faster on the earth. The King got his daughter married to a noble Prince and they lived happily ever after.

Conclusion:- the King and his daughter had traveled very fast, and Brahma loka could have been a really far away place!

Thanks

Amrita said...

Hi,I was reading theory of relativity and found that "Time Dilation is a reciprocal effect",if it is so then why in case of twin paradox,one of the twins who goes to the space and come back, remains younger than the other who stays back on the earth!

November 23, 2009 10:41 PM

Abhay Karnataki said...

good question.
now here we have to understand that though there is no single absolute inertial frame for all observers, you can definitely make out if your frame is inertial or not.
if you are in a car and close your eyes, then even when the car turns, your body bends to one side or other, showing the acceleration, and hence non-inertial nature of the frame attached to the car.
Similarly, in the twin brothers travel, one brother is definitely getting accelerated at the end of the journey, and he is the one who comes out to be younger. the brother in his rest frame doesn't experience any acceleration at any time.
if the other brother would not have returned any time, then the time dilation is exactly reciprocal.

November 23, 2009 10:47 PM

Newton's laws of motion

The Newton's first law of motion states ''A body continues to be in the state of rest or constant motion unless it is acted upon by an external agency.''

The Newton's second law states "The acceleration of a particle is directly proportional to the external force applied on it and inversely proportional to the mass of the particle."

The Question that should naturally arise in a student's mind is, if F=0, what is the need to state the first law separately, because it can be deduced from second law that a=0 and hence velocity is constant. So is the first law necessary!?

Ans:-

The measurement of distances and time are done in a reference frame. The first law of motion defines a reference frame where the motion doesn't change unless and otherwise acted upon by an external agency. e.g. you could be in a car that's going along a hillside region of ups and downs and turns. In a reference frame attached to the car, a particle within the car will not remain stationary or in constant motion. So in such a reference frame, the first law is not applicable, and such frame is ruled out in the Newton's scheme of study of dynamics directly. But you could choose a frame fixed to earth say, in which the first law will hold, even if Car moves around. Such a frame where first law holds, is called inertial frame of reference- inertia of a body is maintained. Now again, a frame attached to earth is not infinitely inertial frame of reference, as the earth itself rotates and revolves. for a trajectory of a plane e.g., Earth's frame becomes non-inertial. So you can use a bigger frame at rest w.r.t Sun. But then even it is non-inertial, when you discuss motion of comets, as the Sun moves in the galaxy... So use even bigger frame at the center of galaxy... and finally even bigger in the outer space in between galaxies and galaxy clusters, so that first law is valid in that reference frame.

Either you can keep changing a reference standard for inertial frame, or you can say that so and so part of the space is a good ''local'' inertial reference frame, observed for a so and so interval of time, over which the first law is valid.

In such an inertial frame, second law can be used to calculate the acceleration 'a'.

Lectures by Prof. V. Balakrishnan

Excellent lectures.

Career in Physics

An enthusiastic reporter,V. Kumara Swamy from "The Telegraph", Calcutta took my interview through emails. Here is the article he published.
My detailed interview is quoted below, as per his questions and my answers:-

1) Please mention a bit about your ambition as a child, your interest in
astrophysics and about your achievements so far.

As a child I was always a curious observer of everything around me. I read the book by Resnik and Halliday and quickly realised that Physics is the subject that brings me closer to my understanding of the nature around me. I was also blessed to have good teachers who could answer my queries based on the reading of Berkeley Physics course and Feynman's Lectures. With this foundation, there has been an undying zest for Physics and I pursue Astrophysics as an Application of Physics to stars and space - an aspect of nature that draws attention of one and all.

2) What are some of the qualities are needed to be a successful researcher in physics?

Its important to have sound background in Mathematics. Mathematics is the language of Physics. Its absolutely necessary to have a good problem solving practise, Physics is a science where you isolate a particular situation in Nature, and study it in detail. Though Mathematics is a great tool, one also needs to remember to constantly relate the formulae and equations to what is happening in reality, in the physical phenomena you are studying. For this reason, students should never neglect any experimental work, and should take every opportunity to do more experiments.

Research in Science needs an attitude to find many different ways and also a zeel not to give up at any stage whatsoever. I also feel that young students should give more preference to learning the methods of science, rather than some particular topic, in selection of area of research. Once these methods are learnt, they could be applied to any topic.

3a) How has the role of physicists evolved over the years.

This question can be answered only by Senior Physicists.

3b)They dabble in various fields depending on their interest, what do think of your own field?

Astrophysics brings to you closer to the vastness of Nature. Here thousands of years are a very small time, and one realizes that one's own body, the houses, cities and such things which we give so much importance, are in reality very minuscule compared to the universe. When you are looking in sky, you are looking in past, because that ray of light has left that star several years ago. So what you see is a collage of past locations and phenomena in different directions.

Over the last century, the advances in Satellite Technology, have given a boon to study of Astrophysics. We are able to probe in farther parts of universe, by collecting more feeble light from the space based telescopes. We are also able to achieve excellent resolution thanks to the CCD Cameras. And only because of fast computers and huge memory spaces, we are able to store and process gigantic data of astronomical images. Most of the data is freely available even to a graduate student, thanks to internet.

I am studying properties of Interstellar Dust, the dust between us and the stars. Its of micron size and is sparsely spaced, however, because of large distances in space, its cumulative effects significantly changed our view of stars and their surroundings.

4) Can you please say a few words about the career progression in anorganisation like the one where you doing your research now. Do you think astrophysics is one field that opens up more doors for research at a international level than any other? In other words, world can be your playground?

I joined the Joint Astronomy Program at IISc, after my MSc Physics in IITB. After 1 year of Research Training Program in special topics of Astrophysics I chose to work in IIA. I had a number of attempts till I started off on my current research topic, and I was awarded senior research scholarship after completion of my comprehensive exam. I visited Max Planck Institute for Astronomy in Heidelberg, Germany, for a one week Summer School related to my research area, and two week mini-project for developing collaborations. I am very glad that my Institute as well as the German Institute gave adequate financial support for the visit.

I feel that in all branches of science, there are excellent opportunities, and they await the explorer.

5) Can you also please list some of the leading institutes in the country that you think give great opportunities for youngsters?

There are atleast 25 independent Institutes in the country. All have their own speciality. All IIT Physics Departments welcome PhD research. Many University Physics departments are also doing good research, subject to availibility of funds.

With the recent hike in scholarships for research scholars, I see research as a very much valid and bright career option. It is stable, exciting, innovative and fulfilling. It is not so much important as to Where you work, but that how you work, and how much you work.

6) Please mention a bit about your own background

I did BSc Physics from Fergusson college Pune, MSc Physics from IITB and I am currently Senior Research Scholar in IIA, as a part of Joint Astronomy Program of IISc.

Physics Studies, exams and Interviews

I receive many querries by students pursuing graduation and post-graduation in Physics, and following are summarised guidelines for them.
Books to read during BSc Physics:-

1. Resnik Halliday, Fundamentals of Physics
2. Berkeley Physics Course, 5 Volumes
3. Feynman Lectues on Physics
   
4. Concepts of Modern Physics:- Arthur Beiser
   

For problem solving :- "Physics by Example" - Rees

Books to be read during MSc Physics:- Follow your Professors..! Don't get too lost in the treatises!

How to prepare for exams, and how to face the entrance interviews for MSc or PhD:-

1. Sit back and revise your BSc/MSc syllabus.
2. Close the books and write down all the Physics you know, from formulae to ideas, concepts.
3. While you are doing step 2, you will recall certain things that you know, but don't remember exactly. Open the books and fill in such gaps.
4. Repeat 2 & 3 until you have good list of ideas in Physics. Now, THIS is Your Physics. What you read till then, was just what others knew. THIS much Physics you know. Its yours, congratulate yourself! One night before the exam you need to revise only this.
   
5. Give as many entrance exams as possible. In any one exam, lets say NET, you don't do well, then come back home and figure out what you didn't do well. e.g you may not have understood Statistical Mechanics well. Then study that before the next exam, and give the next one with confidence.
6. Don't gamble, be careful of negative marking.
7. Do YES!+ program:- www.yesplus.org . Its important not to have just bookish knowledge, but also to have the ability to apply it well, in a relaxed and focussed state of mind, during exam as well as when you face the interview. This is one of the many important benefits you get out of YES!+ workshop.

Projects:- Its a good idea to engage yourself in summer and winter projects in various research Institutes. Alternate your projects in terms of theoretical, experimental or simulation based.

Making Physics Popular at college level

Making Physics Popular at college level
Abhay Karnataki,MSc Physics,IIT Bombay,2nd Year student,February 19, 2003

... the power of instruction is seldom of much efficacy, except in those happy dispositions where it is almost superuous."
This apt remark is a telling comment on the state of instruction and remains as true today as when it was first quoted by Edward Gibbon. There is a natural inclination in every child, starting from vastness of astronomical objects, as to know how this world works, what laws govern the nature around us. Since this is the subject matter of Physics, there is so much a need to us to recognize and implement the best possible and natural methodology of imparting physics. Conventional education bombards the students with a gamut of equations which leaves the student grasping for breath. What is needed is a literature that complements this maths with a lucid physical description of phenomena, so as to bring out its natural properties, and sustain interest and motivation of students.
To this end the books play a very important roll, since the students can spend most of their time with these. Following monumental books form the best foundation in Physics one can have:
Resnick and Halliday.
Berkeley Physics Course, 5 Volumes.
Feynman lecture series, 3 Volumes.
Surely there would be some other combinations, but these are time tested.
Resnick and Halliday develops a curiosity about the methods of Physics and gives a visa to the generalizations of theories, gives glimpses of frontiers, relates the concepts to the real world surrounding us through numerous daily life examples.
Berkeley course endures the student with a rigorous and complete background of future studies. It gives precise limitations and scope of the theory being presented. The problems are very interesting and give an insight in understanding almost all essential basics of physics. Both of the above give excellent order of magnitude calculations, something which is very important to give a feel of the subject.
Feynman lectures are universally acknowledged as being the best lecture series we ever had on Physics. With his endearing charm and uncharacteristically disarming style of an engaging Physics Teacher, Feynman covers most of Physics in a manner that could be understood by a dedicated beginner. However, no Physics course is complete without the tutorials and recitation sessions, in which the students are grilled in the concepts told. This is where above books and educators come in. They are in a position to complement the course by giving due emphasis to the appropriate nuances of the subject and clarify the perspectives.
Apart from the books, the next important thing that brings students close to Physics is the experiments. I strongly feel that there is a need of setting up of the experiments rather than doing just observations of already setup experiments. The students must learn how to play with the apparatus, rather than just number crunching. Certainly, the current group of experiments should be retained, but alongside the students should be encouraged to set up some, possibly without grading them on the basis of those setups.
Following areas are very easy to explore:
 Electronics: let them make some simple liging circuits! ! Even without understanding how a diode works... BSc students could be encouraged to setting up some Power Supplies, Digital counters. And at the final year some experiments that might involve microprocessors.
 Simple mechanical experiments: using gears, batteries, motors, levers, bearings... the aim of these experiments need not be something directly useful, but something which conveys the essential Physics behind actual real life working systems. Third Volume of Berkeley Physics Course, Waves, provides an excellent set of home experiments.
 Computer programming: Computers should be brought into the work experience of students at an earlier stage. Without bothering too much about the details of programming languages, they should be given a first hand experience of the softwares available. Internet education plays an important role in fast and up to date knowledge of the subject. It has broadened the capacity of the individual to access the vast amount of data. Following activities would be of interest:
-function plotting using softwares.
-plotting trajectories of charged particles in various combinations of E and B fields.
-generation of fractals.
-viewing 3 D images of solids.
Study of classic experiments: some of the classic experiments like Millikan's oil drop experiment, J.J. Thomson's e/m measurement, Michelson's interferometer which are possibly available to undergraduates, should be studied in very much greater detail. The constraints of time should be uplifted from the students, so should be the burdens of being evaluated for doing the experiment, and its completion. For, the spirit of scientific adventure ( so essential for the joy of doing Physics) can be experienced only in a liberal academic atmosphere free from such mundane constraints.
The courses should be designed so that there is maximum correlation of theory taught and experiments performed. The idea should not necessarily be to cover the entire syllabus, but to convey the essential physics in the subject and to inspire the student by conveying the personal excitement of learning the subject. An inspired student will learn much more on his/ her own, than what can be taught in the class rooms. A certain care about delicate balance of students' psychological, emotional inclinations is to be taken by the teachers. I believe that there are no bad students, there are only fast and slow students. Some people grasp some things fast and some do it slowly. There should be both, freedom and care, on the part of the teacher. Teachers can give freedom to self progress and go much ahead in the subject to the fast students, and they have to pay more attention to those who grasp it slowly.Only a good work culture in the class can impel simultaneous growth of all. To help this grow, assignments can be given by clubbing fast and slow students, where slow students present the conclusions of the work. Such group discussions and seminars of students would be very helpful.
"Problems for toffies" - this is something which works very well! The idea is to have healthy competition with excitement of prize.
Another activity that can be encouraged is reading of simple, early original papers. These are the landmark papers, which mark the history of science, and milestones in scientific progress. Since the facts discovered then, are now firmly established and have became accessible to the novice, the concepts in the papers are easily understandable. On the other hand, the joy of discovery presented in the original papers is unmatched by any later substitute on the same topic.
Often we can celebrate the birth anniversery of a Physicist, with a series of discussions of his/her best works. A wonderful course on Classical Physics through work of Sir G. I. Taylor is being offered in MIT and Harvard. It is an excellent example demonstrating how a single scientist's work can be so beneficial and illustrating with a wide variety of research areas.
I thank all my teachers who guided me and introduced to the fascinating world of science and in particular Physics.
Let's make learning Physics a celebration.


PS. This article won first prize in a Science essay competition. It was briefly edited by my then friend and now scientist, Ashutosh Jogalekar. You can visit his blog .

Berkeley Physics Course now available

I love Tata McGraw Hill Publications... they bring out the best of the books in the world to Asian students in an affordable price!
Now they have revived the Classic Physics textbooks:- the Berkeley Physics Course:

Vol 1 Mechanics
Vol 2 Electricity and Magnetism
Vol 3 Waves
Vol 4 Quantum Physics
Vol 5 Statistical Physics

These books will tell you the Graduate Physics in the most precise form! They give you the scope and limitations of the theory presented. The third volume Waves is filled with ample illustrations and experiments. The exercises given will sharpen your skills.
Second volume on Electricity and Magnetism, the Nobel Laureate Purcell has described in a diagramatic and a very illustrative manner, how accelerated motion of a charge gives rise to electromangetic radiation...
Learn Physics from the Best!

Nurture the Talent

Nurture the talent

Its our Founder's day in my Indian Institute of Astrophysics today. We had a public lecture by Prof. C N R Rao, the eminent Scientist. Check more about his excellent research career, the extraordinary awards he has received and other information on his website. The Auditorium was housefull and we had standing audience!

In a fantastic talk on "Science in India, a personal recollection", he spoke with all humor the ups and downs in research. His 50 years of experience in building research institutes, guiding students, was evident. He stressed the need on nurturing and encouraging talent in all possible ways for study of Science. He said the funds are now available, in contrast to 40-50 years ago, and we need to give quality results. He asked us, the researchers, to abandon mediocracy and choose the most interesting, important, problems for research. He said, we need those "nutty fellows", the bright young minds, who don't care what other people think, and get themselves immersed in study. He said, we can't discipline scientist like in military, but we need to bring the best of the young minds by taking them beyond their comfortable capcity.

He cited how, even with limited facilities and funds, even in old days there used to be some scientists who would do their best work, and it would meet the international standards. Talking about our Founder, he said, Vainu Bapu was a very methodical and eloquent speaker, and always insisted on excellence.
More about my Institute, check on the website.
Tomorrow also we have a nice talk on "My experiences in space". A talk by an Astronaut! Come and book your space before time, as I know the auditorium is likely to be housefull as today!