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!

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'.

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.

Physics of Flame

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

 

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:

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:

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 of 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.

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.