Thursday, November 27, 2008

Physics of Flame

Deep Physics lies hidden in simple phenomena around. This week, let's see what a candle flame can teach us:

21nov 009 

When I take photos of the candle flame through my Kodak Easy Share C533 camera, I get different photos on different settings. This Kodak Digital camera is a simple point and shoot camera. Same candle showed up as follows in another picture:

21nov 010

Q.1: Compared to the first picture, why is there so much sideways glow in this picture?




Q.2: Why is the shape of the candle flame like a tapering upwards always?

Q.3: What would be the shape of candle flame, in place where there is no gravity?

I took further close up photographs of candle flame with my Kodak Digital Camera. Here is the picture:

21nov 015

Q.4: Do you see the color distribution between blue and yellow? What gives rise to the two colors? What decides the position of these two colors in the flame?





To verify whether its a feature only 21nov 020of wax candle flame, I took photograph of a glowing matchstick:

It also shows the similar features, indicating the same Physics governing.

Answers below[can you spot them? :) ]  :-

Ans.1. the glow captured in the camera depends on the exposure setting. The molecules are exciting and de-exciting at a rapid rate. The de-excitation is very fast, 10^(-8)sec, but the excitation depends on the temperature in that region. In the second photo, wider region is captured, indicating larger exposure time.

Ans.2.Fluid dynamics of simple laminar flow... Its same to the flow of water when you open it at very slow speeds. This is flow below the Reynolds number. Above Reynolds number, the flow is chaotic, as can be seen in the case of smoke from an incense. 

Ans.3.Sphere !? :) that's my guess... 

Ans.4.higher temperatures give higher excitation and de-excitation, resulting in blue. Only two colors are seen corresponding to energy levels available. the position shows the temperature profile.

Wednesday, November 26, 2008

Friction - Evil or God !

Everywhere you see, one is attempting to reduce Friction. E.g. the lubricating oils in ball bearings, door hinges. However, have you thought about what would happen if there was no Friction!
Without Friction, you can't even walk on the floor! That's what happens, in rain, if the floor is slippery, you tend to fall down. Why, because the Friction has got reduced. Its a strange thing that the force of Friction, which opposes every motion, is actually supporting the entire mechanism of motion!
Let's say you want to walk. Now suppose you were in Space, then unless someone gave you a push, you wouldn't move from where you are! So when you walk, what you do is you push back on the ground. The only way you can push something is when you have some grip over it. That's Friction. Without Friction, when you attempt to walk, you will actually roll over and fall!
When a wheel moves on the floor, three things can happen: It can slide like a sledge- this happens when your wheels are break locked and there is no rotation of wheel, or It can rotate without any translation, as it happens when a wheel is stuck in a ditch of mud, and any amount of acceleration only gives it rotation, no translation. Third thing which is expected, normal behaviour, is rotation and translation. This can happen only when there is adequate Friction.
What is Friction. On a microscopic level, the smooth looking surface is not a regular plane. There are hills and valleys at atomic level. Whenever two surfaces meet, they form temporary contacts, and molecules of one surface invade in hills and valleys of other surface. They interlock and push each other. So if a top surface is moving forward on a bottom surface, the bottom surface pushes the top one back, and the top surface pulls the bottom one forward.
This is easily seen in case of liquids. The analog of Friction is Viscocity. An Oil is more viscous than water and Honey is more viscous than Oil. In a mixer, when the blade rotates, it carries along with it the layer of liquid next to it, and that layer drags the next layer with it and so on, the subsequent liquids are set in motion. Had there been no Viscocity, you wouldn't be able to stir your coffee!

Tuesday, November 25, 2008

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.

Current & Voltage

Prasanna sent an interesting Question. This is how Science progresses, with curiousity aroused by practical needs. Here is the question:



The following Amaron 12 Volt lead acid battery. 


It ran out of charge. I had with me 8 1.5 volt Duracell batteries as the one below.



Can I connect 8 of them in series, total voltage will be 12 volts and use them instead of the original Lead acid battery.


Can you explain? Write your answers in Comments.

Will come up with an explanation soon.

Monday, November 24, 2008

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:- . 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.

Stability of Vehicles

You think you do a big job when you are balancing a 2 wheeler while driving it? You hardly do anything! A major role is played by rotating wheel. To see why, just imagine yourself balancing the 2 wheeler that is stationary, for as long as you generally drive! Balancing a stationary 2 wheeler is tough. Do it with cycle, you will have to do some good amount of acrobatics!

Why would a rotating wheel be more stable? What is fall of a bike? Its essentially tilt that doesn't reverse, and continues till it touches the ground. A rotating wheel, when tilted, actually turns - that's how you take turns - rather than falling by side.

A complex mechanics equation and formulae and vectors show why this is necessary. To get a simple idea, think of it this way:- a sledge moving on ice has a tendency to move in the same direction. If you apply sideways force, the direction of motion will be very slightly changed to that side, while it continues to move in more or less same direction.

In case of rotating wheel, it has a tendency to continue to rotate around the same axis - say the axle of wheeel - unless you tilt it. When it is falling, it just shifts the direction of axle - like the small direction change in sledge motion - and continues to rotate around this new axis.

When a wheel tends to fall, instead of falling sideways and continuing to move in the same direction, it will change the direction of travel, and spiral towards fall. This is easily seen by anyone playing with a cycle wheel and pushing it by hitting at back. The wheel will roll on, and depending on which side it bends, it will spiral in that side and fall. What it doesn't do, is to go in straight direction and fall sideways!

Spinning top also shows the similar stability. It can balance itself on a needle end. It will keep balancing and rotating and once friction eats up the energy, it falls down spiralling.
It also shows another behaviour, when, after throwing it may not have landed vertically, and slight tilt causes its rotation axis to go in circle around the vertical axis. Notice that even though its tilted, because its rotating, it goes in circles, rather than falling down. A stationary top will simply fall down. This is called as Precession.

The larger the speed, more the stability. Of course, more speed invites other dangers.Also, this means that falling sideways is much easier on smaller speeds and sharper curves. So be careful!

Saturday, November 22, 2008

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!

Thursday, November 20, 2008


True to my religion, Physics, I thought an article on Astronomy and Astrophysics is a must! What you see above is how the sky looks like in a less than a degree field of view in a region of Large Magellanic Cloud, our next door galaxy. The image is taken by Ultraviolet Imaging Telescope.
Isn't it unbelievable that in that small part of the sky there are so many stars! And its so very beautiful. As if there is a Diwali in that galaxy, and all those are houses with diyas lit up on their doors.
And another amazing thing about sky-view is that, when you look in different directions, you are actually seeing light that originated in different times from those stars, so there is a temporal information encoded in the picture! What you see is a spatial collage of different pasts in various directions..

Wednesday, November 19, 2008

night sky of the World

night sky of the World

Above picture shows how much city light is emitted in different parts of the world at night... recorded by some satellites. More info is here:- night sky in the World. interesting, isn't it!

Tuesday, November 18, 2008

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!

One hour day and Half hour night

I always feel grateful for being in a Research Institute. Its this sheer opportunity to meet some of the most brilliant people on the planet. Today we had a talk by the Astronaut Claude Nicollier, "My experience in Space".He showed some amazing pictures of the earth from space, it was simply fantastic to see the entire Himalayas in one picture. Also, the distribution of river Ganga where it meets the ocean.
It was also an absolutely stunning picture to see that on top of one of the desserts, the cloud coverage is exactly on top of the sea, and it ends on the coastline.

Absolutely passionate about his work, he mentioned how he had undergone rigorous training in water chambers. Their first mission was repair of the Hubble Space Telescope. Imagine changing parts of a huge (2 meter diameter) telescope in space! In those water chambers, they make exact replica, with high fidelity modelling, of the space telescope. In space you need to stabilize your body, and move very slowly. They practised it for months before the mission, in the water chambers. Exact and detailed planning, even practise of handling unexpected failures and problems.

When you are in space, you are in a very low air pressure surrounding. Say 1/3rd of that on earth. So the nitrogen tends to get into the blood. There are Air Chambers, where you increase the air pressure to normal ones on the earth, and rejuvenate yourself. Claustrophobia is the fear of enclosed spaces. If you have it, then these small Air chambers are not meant for you! Also the Astronaut's suit can be very cumbersome to get into and carry along.

You can see here a photo of a pair of astronauts repairing the Hubble Space Telescope. Notice that one astronaut has firmly grounded his feet on the robot arm of the space ship,(you don't see the spaceship, the arm is the white rod like thing in the photo), and other Astronaut is freely floating. Whenever the Astronauts are doing such work, doing space walk, they are attached to the space-craft by a thread: they are tethered. This is to ensure that they don't just get lost in space by mistake! As he jokingly said, if an astronaut or a repair tool is lost, it becomes a useless satellite to Earth! So all the repair tools and parts are also tethered to the spaceship.

As you are orbiting, you have sunrise and sunset more often! You get 1 hour of a day and 1/2 hour of a night! Of course, you don't go to sleep in that night when you are in shadow of the earth. So you need to get used to this kind of bright and dark timings. Before the Earth becomes totally dark, and Sun goes behind it, you can see a beautiful cresent of the Earth! The moon also rises and sets quite fast. The sky is absolutely dark, and you can see Sun also as just another, closer, brighter and bigger star.

On Earth, our body has mechanisms to push lot of blood supply to the head. So much supply is not needed when you are in space. Lot of body fluid imbalance and loss of orientation can happen when you just reach the space. So if you are planning to visit and go for a space ride, be prepared for some phisiological unpleasantness! He said its like sea-sickness.

To become an astronaut, he said, you need good physical fitness, sound mental balance, and a sound educational background. After that, its a luck to be selected, as there is lot of competition and few jobs available!

A Physics Graduate, who did research in Astronomy, and took over Air Pilot job, and then worked as an Astronaut, Claude Nicollier is now full time professor in Lausanne, inspiring young students to the thrill of Space research.

Tuesday, November 11, 2008

Diwali crackers

I saw this cracker rocket in Diwali, I don't know how it could go zigzag, like a snake in the middle of the air. Can you figure that out.It also whistles.

Monday, November 10, 2008

Properties of light - 2

I almost can't show to you how my fan is rotating. Here is a photo of a rotating fan:
It looks stationary!
So I changed the setting on my camera from auto to night mode:
Night mode has lot of light gathering due to large aperture and longer exposure. So you see the blurred image, and because of flash reflection, you see the 3 pans too. Two bright lights are tubelights.
And when I put it on fireworks mode:
Its a very long exposure mode. Its more or less what my eye also sees. So what our eyes see and what a camera sees are different worlds! Here is a video of the same fan. Which way is it rotating?


In the video, it apears to rotate in the opposite way than in reality! This can be seen by switching off the fan:


!!! ??? So how come this illusion!!! ???
You may have taken photos like this one:
Now as a traveller, your eyes won't see such an image, wherever you look, you would see things pretty much clear only( Unless you are travelling in some super fast train!).

Whether eye or camera, each observing instrument has a characteristic exposure time, the time for which the instrument gathers light information, stores it, and then takes next information to process.
This also shows how versatile our eyes are! They are very powerful cameras!
The opposite motion of fan is due to the frequecy of camera capturing the frames of video. If it was a single pan rotating, the video would be different. It would maintain the same sense of rotation. Here, three pans replace each others' positions during the frame re-capture time, and it is done with a lag, so gives a sense of opposite motion than real.

The time taken by eye to take next frame is called Persistance of Vision. Long exposure photos often show nice slow motion, as people observe in motion of stars:

Of course, the stars appear to rotate because we are rotating!

Anytime the exposure is longer enough than the motion, we get a streak photo, as seen in the fireworks here:

Wednesday, November 5, 2008

Immiscible liquids

I know the topic of this week and next is light, but here is a curious observation I had tonight, I thought of sharing with all aof you. 
I had a late dinner in our canteen today. The soup that I took, had a 6mm layer of oil on it! I was quite surprised, as the canteen food is not thaaaat bad! 

Why do you think it had that much oil...

Come on think think!!
See a Physicist can be a good detective too...!! 
So the solution is...
Have you given up??? ............. ? ?     .............  :)
The oil in the whole soup mix was stirred and mixed well when it was made. Since I went late, by that time, these small droplets of oil in the mixture, came together, since they don't mix with rest of the soup, which is more of water. And started floating, since the oil is lighter than water!!

That solves the mystery!! :)
You can do this experiment:- Take one spoon of oil, mix it in mixer with 200ml of water. You can have a color added to the water, say blue ink, to see the oil and water separately. After thorough mixing, leave the mixture for 15 minutes. the oil will separate and start floating.
Oil floating on sea water, after Kuwait oil wells had got destroyed is another example of immiscibility and floatation between two liquids.

Tuesday, November 4, 2008

Properties of Light - 1

I like to see Physics in everyday life. Physics is not a matter of book only, it brings you closer to the Nature.

Here is a photo I took in the Diwali celebrations:


Do you see two reflections!? Can you justify why it happens ?

The theme this week and next is Properties of Light. Send in your querries on this topic, and I will do my best to Answer them!
Posted by Picasa

Tuesday, October 28, 2008


Here is a fantastic experiment demonstrating magnetism and angular momentum.

Saturday, October 25, 2008

Q n A - 2 :- learning Physics during train travel!

I am happy when people recognize me as a Scientist, in particularly as a Physicist. In the train journey from Bangalore to Mumbai last night, I found many interesting youth in my compartment, asking lots of interesting physics questions. Here is roughly how the dialogue went on for almost two hours! Thanks to Alpa, Girish, Akhilesh, Keyur and Jitender for being such curious students!! And I like being grilled by questions, so thanks for grilling me!! :)

Q: What is the expected outcome of Large Hadron Collider? Can we create another planet from this experiment?
Ans:- Hardly! in LHC experiment,They are colliding two protons at a very high energy. Now, what do you think of a proton as? A kind of solid spherelike a cricket ball, but a tiny and very low mass one, right? In reality, even the proton is made up of smaller fundamental particles, called "Quarks".Now these quarks don't generally leave the spherical boundary of the sizeof the proton. However, when two protons collide on each other with so much energy, these quarks can break up into various combinations, and new particlescan get formed.
Q: So how does LHC experiement give rise to a new Big Bang?
Ans: It doesn't create a new big bang!! Its like this: When Big Bang Happened,Huge amount of Energy was packed in small region of space. And the laws ofPhysics as we know are not valid for such high energy densities. So we cannotstudy the physical situations very very close to Big Bang time. (We can, however,Go upto the microseconds after the bigbang!)So when two protons in LHC collidewith each other, what they do is they pack in a lot of energy in a very smallvolume, thus making a laboratory controlled situation similar in few aspects, to the big bang.
Q: So is it really worth spending all the money, on this biggest experimentof science? Cant we not use it for some social cause?
Ans:- I don't think that social causes are not being taken care, and lack onlymoney. Scientific advances have far reaching consequences not known beforehand.E.g. The GPS system which you use, would collapse in few minutes if the Einstein'sGeneral Theory of Relativity is not used in their calculations. Now GTR givesvery minute corrections, and most of the times we can use Newton's theory of gravitation. However, when your hand receiver gives out signal to 4 satellites,and they correlate their positions and send you back your location details, if they don't apply proper corrections for their positions, then your locationwon't be accurate at all! So who knows, results of LHC experiment may bring outsomething not forseen right now.
Q:So what is your research topic?
Ans:- I am studying the properties of interstellar dust, that between us and the stars. This dust obscures the starlight, and scatters and absorbs it, thusnot giving the correct picture. Its just like a cloud covering the sun. So if I know the size, constituents, spatial distribution of these dust particles,then I can account for their effects.
Q:- How is this dust?
Ans:- Its micron size. Anything more than a hundred atoms bound together is termed as dust. Q:- I thought space was all vaccum, how come so much dust, and how significant is the obscurration?
Ans:- YES, it is a very high quality vaccum out there. Its better than the bestthat can be achieved in laboratories... Still, inside the galaxy, there is lot of hydrogen gas, and also these dust particles.And there is hardly one particleper cm^3, but the distances are so Huge, that it adds up to a large quantity.
Q:- What is this dust made up of?
Ans:- Its largely silicates, oxides, carbon and ice.Q:-If we see a spectra of dust, what do we exactly see, the dust, or the sourceof the light?Ans:- The scattered light will be of the same frequency as the source. The dust absorbs some light, and gets heated up, and emits in Infrared, just likeeven now all our bodies are radiating in Infrared. Now some of the absorbed lightwill excite the atoms in the dust to a higher level, and when it de-excites, it will emit the spectra charecteristic to the dust constituents.
Q:I just don't understand all this, Big Bang and stuff like that. What was therebefore that?
Ans:- Yeah. This is a limitation of linear logic. You will always ask, what was before whatever you know, and what is after whatever you know! Another scheme of logic is spherical logic. Its like this, on a sphere, what is the starting point of the sphere? Any point could be a starting point. This is a gift of Indian Philosophy to the Scientific thinking. There is also a theoryfor beginning of universe, that there was not just one big bang, but millionsand millions of big bangs. Right now there could be something like a Big Banghappening in a distant part of the world!Alpa:- Right now there could be other copies of us sitting in some other part of the world! Me:- Yes very much possible!
See this article.
Q:What is dark matter? how come it became known recently?
Ans:- Its non-barionic matter, matter which doesn't give out electromagneticradiation. Protons are barionic matter. Recently, Astrnomers studied the velocityof hydrogen in different parts of the galaxy, and plotted it from the center of galaxy radially outwards. The velocity curve flattened after a radius, and thiswas not acceptable, gravitationally, if you assume that only the luminous matter is present.So they had to suggest a large amount of unseen matter, which theytermed as dark matter. In absence of any such matter, the curve would have gonedown, instead of remaining flat.
Q: What if I emit light from a car travelling at the speed of light!? Will I see it in front of my car?Ans:- First let's consider a simple situation. Lets say I am standing here, and you are travelling in a car at speed V1. And you throw a ball at speed V2 in same direction. Then I would notice the speed of that ball as V1+v2, right? Now consider the case of light. If you are travelling at speed v, and throw light, which will travel at the speed c, then I will also see the light travelling at speed c!! This is a kind of miracle! This is an experimentally verified fact,and This is subject of relativity, where our notions of time and space are totally changed! E.g. If Akhilesh travels from here to a distant galaxy and comes back, he would find himself younger than his cousin, whom he left at the same age!! This is because, not just clocks, the heartbeats, the wheels, the time itself slows down for a moving observer, w.r.t. a stationary observer!!Girish:- There is a nice description of this in Concepts of modern physics byArthur Beiser.Me:- Yes, and Relativity is not difficult! With pen and paper I can describe to you in few minutes!
See this nice illustration.

Q n A - 1

1) This is w.r.t the image on ur blog. See the image, the reflection of the turtle is seen on the water surface. How is this possible considering light is reflected of the surface.
Ans: first the light enters from top of water to the turtle's skin, gets reflected/scattered and reaches to the water surface. Now when it is approaching from below, it gets totally internally reflected...

2) In a laptop screen only for certain viewing angles of the monitor, can the images be seen clearly. At other angles the images cannot be see. Why is this sp.
Ans: The laptop's pixels are like little torches, made up of a substance called liquid crystals. These send light, like a torch, in a cone shaped beam. so if you are out of the beam angle, then you don't see a good image!

3) People say if only google webpage had a black background, then so much electricity would be saved. How?
Ans: The white and other colors need electricity to switch on the little torches on the computer screen pixels. The black color is just absence of any light at all. So showing a black background would save electricity in general. particularly, since millions of visitors use the google page daily, it will save lot of energy.

4) A car requires a 12 volt DC battery. These batteries are huge. I have 8 1.5 volt AA size batteries. Can i connect them in series and replace the car battery.
Ans:- Lets see what a battery is. It has chemicals that keep the positive and negative charges piled up with some distance in between them. Now the voltage depends on how much charge can be piled up, and current on how fast this charge can be transfered. a small 1.5 volt battery can't withstand a fast moving charge flow, as needed in a car. A car battery has a high current rating, e.g. to give the ignition spark. So in case of batteries, the current rating is important along with the voltage.

Tuesday, August 5, 2008

Transverse and Longitudinal Waves

If the motion of particles is perpendicular to the the direction of propogation of wave, these waves are called Transverse waves. If the motion of the particles is parallel to the direction of propogation of wave, its called the Longitudinal wave.

Simplest examples:
Waves on a rope: Transverse
Sound Waves: Longitudinal

Light is a transverse wave, the E and B fields change perpendicular to
the motion of wave...

Thursday, July 31, 2008

General theory of relativity

A profound theory that is basis of day to day life now... Our GPS system is based on GTR, and if GTR corrections are not used, the whole system would collapse in a few minutes! more about GTR Will come here...

Fluid Dynamics

everything is fluid, of some kind! even glass "flows"- the windows of old houses are found to be thicker at the bottom. More about Fluid Dynamics here.

Faster than light!

After the advent of Special theory of relativity, its a well known fact that matter cannot travel faster than light. However, motion of some blobs in astrophysics gives and "apparant velocity" greater than c, the speed of light. I will discuss the geometric basis of this effect.

Angular momentum

Angular momentum is a very fascinating topic... I will be writing a post on this soon...

Total Internal Reflection and Quantum Tunnelling

Everyone knows that light while travelling from a denser medium to a rarer medium bends away from the normal. This is the reason why a teaspoon in a glass of water looks broken!
Now imagine that the angle of incident ray from the denser medium increases. The ray will come out at larger and larger angles from the norma, in the rarer medium. At a certain critical angle, the outcoming ray will come on a grazing angle, it will be almost parallel to the surface between denser and rarer medium. And then, for larger angles, no rays come out, they are totally internally reflected!!

What a fantastic phenomenon... Its responcible for rainbows... the light rays get totally internally reflected inside the sphere of water before coming out, and get dispersed in the process. Check out this cool video showing how after certain angle, the laser light is totally internally reflected: - Youtube Video.

Another magician's trick can be explained. Suppose a magician pours water in a glass containing a coin, and the coin disappears! :) How it happens is seen in this video.

This fact of reflection of light is put to a great use in transport of light through small tubes. This way of reflecting the light is total, there is no transmission loss. Here is a nice video of Harvard Professor explaining this.

In the following image you see the Total Internal Reflection of the image of the turtle!

When you look closely at what is happening, certain questions popup in your mind. After all, light behaves as wave also, and even in its particle nature, how is it that a photon would know, whether it has to get totally internally reflected, or just come out of the surface!
What actually happens is something like this: the light waves inside the denser medium are sinusoidal. When they reach the surface interface, they sample the space outside, in terms of exponentially decaying fields. If the material is not dense enough, they return back!
To taste the validity of propogation of fields into so called "Classically forbidden" region, we can do an experiment. We can keep a denser medium after a gap of rarer medium. Voila! Its found that the wave has propogated into the denser medium inspite of the gap! This is called quantum tunnelling or frustrated total internal reflection.