Preferential cooking

If you take Channa dal and Moong dal, any cook will tell you, that Channa dal takes much longer to get cooked. Say 5 whistles. Whereas Moong dal can get cooked in 3. Now in case you want to make mixed dal, and put both of them together in a cooker, even if you give 5 whistles, you find that Channa dal is not cooked, and Moong dal is (naturally) over cooked, almost ground. Why is that Channa dal didn't get the required heat, even after giving 5 whistles!?

The very fact that Channa dal takes longer to cook, implies that it has less heat capacity. When we supply the heat to the mixture, the Moong dal with lower heat capacity absorbs more heat than Channa dal, and Channa dal remains un-cooked !

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'.

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:- 

GPGPU General Purpose Graphics Processing Unit 

CUDA Compute Unified Device Architecture