### Recent Posts - page 7

• #### Understanding Nuclear Physics through SCILAB.

Nuclear and particle physics through Scilab.

• #### How best to prepare for UGC, CSIR-NET

If you are to come out of a NET that traps you. Stratagem.

This article is purported to be helpful towards those who take Indian “after the university” entrance exam known as NET (National Eligibility test governed by CSIR; Council of Scientific and Industrial Research) which is held twice every year.

NET for science subjects is known as CSIR-NET and arts/humanities as UGC-NET. They are conducted at different times and by different agencies.

Manmohan sir, I want to qualify net. … any suggestions ?

Find an algorithm at the end for a quicker assimilation of the strategies given here. Both pdf and jpg are available.

I am assuming you will take the test in June 2018.

Solve 10 previous papers thoroughly.

Make a categorization of subject wise weightage: eg mathematical physics, quantum mechanics, thermodynamics etc.

Set yourself a good score based on what you think you can certainly achieve. Make a 15% increase and make that your target.

See your strongest subjects and make a plan which ones you want to be thoroughly prepared about so you can arrive your target.

Never attempt a question, unless you are very sure of it. Negative marks in net can ruin your chances. (By attempt I mean: select the choice)

Decide in which section you want to score how much.

In section A (total marks 30) try to achieve full marks, except a few daunting questions. Getting 22 (11 questions right, assuming no negative score) seems a good idea. In section

• #### Cross and Dot product of vectors.

Someone asked a very interesting question on the role of vectors in Physics. He was curious to know if dot product of vectors is natural but vector product is just syncretism, — that is make shift or unnatural manipulation.

Every vector can be resolved into two components. The cosine and sine components (any two vectors would constitute a plane) while cos part can represent the projection defined through dot PDT we can’t leave out the sine part. It plays its role through the vector or cross PDT.

The vector direction is no more along same direction as original vectors because of orthogonality. To preserve symmetry of both orthogonal components (or equal footing of both vectors, vector a and b eg) we need the 3rd dimension. Hence such a definition of cross PDT.

Eg the emf generated in a changing “mag field” (Faraday’s law) depends on change in mag field if area is held const. It also depends on change in “area vector” if mag field is held const. So there are two vectors involved and their transverse values matter (and not their longitudinal values). To preserve equivalent role of both area and mag field vectors the resultant vector must be in a 3rd orthogonal direction …

Also think of this; a scalar is not necessarily directionless. (think electric current or even temperature or heat gradient etc) They just do not have the full fledged capacity of vectors. Its like flower bud vs fully blossomed flower.

So scalars can’t be added like vectors. We tend to make a mistake here. We say scalars don’t have a direction. That’s totally erroneous. They do have direction and it matters. Which direction you want to stick to if the current flows along certain direction only?

Lets make it still more clear.

If there are two directions in which there are electric currents, we say they are both equal, the direction won’t matter. That’s where we make the mistake. We should say they are equivalent and not equal. Equality is ideal, its mathematical. But equivalence is physical. Its the effects of both currents in a certain sense that make them equivalent, but their strict equality does not follow.

• #### April 16.

Reminiscing a dreadful day in my life. Today 16th April, a decade ago, 2007.

It was early morning. Snow flakes were making the surrounding really beautiful. Especially because I was sitting inside of a cozy air conditioned student center, looking out of the glass wall. The hazelnut flavored milk-less coffee used to be one of my favorite, especially when I would be sitting alone. I was reading a paper on “phenomenology of quantum mechanical phases related to my thesis research”. These were the days I had started writing or at-least musing about writing blogs. So I was even perhaps in the mood of writing a poem or something.

The beautiful silence was broken by a strange noise of a crowd. I looked around. A man with a long gun, as long perhaps as himself, of-course a bit smaller, wielding it to the ground was hailing at the folks around “stay indoor”.

• #### Interference of two types

Interference by wave-front and amplitude splitting.

Optics Series Lecture, Lecture – XIV, XV, XVI.

Topics covered in this lecture

A. Color of thin films

B. Newton’s rings

C. Lloyd’s mirror and

D. Phase changes during reflection

We have previously discussed what is interference and what are wave-front splitting and amplitude splitting interference. We have also discussed in much details two wave-front splitting interference viz.

a. Young’s double slit interference, here — Lecture — IX, and

b. Fresnel’s bi-prism, here —  Lecture – XI.

Today we will discuss one more wave-front splitting interference namely Lloyd’s mirror interference before moving onto the amplitude splitting interference of the Newton’s rings.

Also we will discuss two interesting and related concepts;

i. Phase change on reflection and

ii. Color of thin films

Today we will discuss one more wave-front splitting interference namely Lloyd’s mirror interference before moving onto the amplitude splitting interference of the Newton’s Rings.

Also we will discuss two interesting and related concepts;

i. Phase change on reflection and

ii. Color of thin films