Thursday, December 3, 2009

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

All the best!

Wednesday, December 2, 2009

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!
Blogger 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

Blogger 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

Friday, November 27, 2009

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!?

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'.

Tuesday, July 28, 2009

High-performance Computing using Graphics Processors

Dr. Rekesh Mohan gave a very interesting seminar in our Institute recently. It was about the use of existing hardware used for graphics applications for high performance computing. 

An important recent trend in high-performance computing is the use of hardware originally designed for graphics and games to solve general purpose computing problems. Modern Graphics Processing Units (GPUs) deliver enormous power for arithmetically-intensive computations, at extremely low cost and power consumption as compared to CPU based computing clusters. 

The existing programs need to be modified using the syntax that can be understood by the Graphics Processing units. This requires certain libraries and commands. The speed could be enhanced to 10-100 times, and is cost effective compared to parallel CPU cluster method. 

Check here for two platforms to use for GPU programming:- 

Monday, July 27, 2009

Lectures on General Theory of Relativity

Lectures on General Theory of Relativity, by Prof. T. Padmanabhan have been uploaded here.

T. Padmanabhan is a renowned Physicist who has written excellent books on Theoretical Astrophysics.

Tuesday, July 21, 2009

Forming monolayer films

The water contains loosely bound Hydrogen nuclei in bonding with the OH radical. The molecules can have afinity to water depending on their polarity, if a molecule can contribute a positive charge, it would bond very well with OH negative radical. If it has negative polarity, it will be repelled from OH radicals. So any typical molecule will have either a crowding of OH -ve radicals around it or it has H+ ions around it. The situation is special when it comes to bipolar molecules, and if they are sufficiently long, they will attract both OH- or H+ at their ends. If the molecules are long, then they have sufficient space to accommodate different radicals on both ends. Surfactant molecules look like these:-

They are long chain molecules with a "head" that is water-loving :- water philic. the tails are water phobic, and hence in the given surface interface between water and air, they tend to stand upright as shown. Just like when you dip a plate in water, some water clings on the surface of plate, a metal can be dipped into a surfactant solution, and it will come out with a layer of the surfactant molecules. However this needs to be done very slowly. Here is a good article on this method of forming monolayers of one substance on another. Here are some good diagrams of the process.

Wednesday, July 15, 2009

Heartbeat of the Sun

One of the greatest opportunities in a research Institute is to get to listen to great Scientists. Here is the news article describing how a team of scientists studying Sun is extracting the information of the internal activities of the Sun. 
The studies of Sun using Visible or any other electromagnetic radiation is limited to the photosphere. Only Neutrinos produced in the nuclear reactions at the core of the Sun carry information about the layers inside Sun, to us. In what amounts to finding needle in the hey, the scientists have discovered a subtle ripple in the overall movement of the solar surface. The technique is to get the Fourier transform of the Fourier transform, thus giving an indication to the patterns in the frequency spectrum! It is like finding the octaves in the music of piano, and detecting the presence of piano in a grand symphony. The waves originate at the core of Sun because of gravitational disturbances. Rafael A. Garcia, DSM/DAPNIA/Service  d'Astrophysique, France explained this in a colloquium at our Indian Institute for Astrophysics.

Tuesday, July 14, 2009

Mysteries in Sound Phenomena

One friend asked, why in the place that is an empty square covered at a sixth floor ceiling and surrounded by classrooms in a college, echos a lot? 
After some discussions, we came to a simple conclusion: they had used that place after college hours, when there is absolutely no-one in the college. During the day-time, when it is flooded with students, it doesn't echo at all! The absence of students here, is giving rise to a lack of any absorbing medium for the sound energy, and it finds it easy to bounce back and forth. This effect can be seen in any empty place, flat, hall, most famous being the hilltops, as the sound seems to come back from distant hills.

Our staircase has hollow pipes as hand railings. I was having fun striking the metal with my metal keys, and it would create quite a sound! I checked striking on different sized pipes, and the sound is so very different! When the metals being stroked the same, why did the sound differ?
The energy of the stroke gives rise to an impulse of vibration in the solid of the pipe. This impulse is a superposition of a huge number of frequencies. These all frequencies get transmitted to the air within the pipe. Due to the size of the pipe, the back and forth oscillations are sustained only at the natural frequencies of that length and radius of the pipe. So the standing waves are dependent on the radius of the pipe, thus giving different sound in different sized pipes.