The wrong questions and responses in GATE 2018, Physics. Reply

Here is a summary of the questions which has possibly been set wrong (I have given details below) or numerical answer types whose answers have been given incorrectly as per the declared answer sheet.

Q8. The magnetic field also has a odd parity. Not “E and A only”. Since that choice (or “none of the above”) isn’t given, clearly the question has been set wrong. See here.

IMG_20180220_193219_2

Q3. The Stern-Gerlach experiment evidenced space quantification of angular momentum. The Zeeman effect evidenced the existence of electron spin. That choice isn’t given, instead answer sheet gives the opposite as the correct answer. See any good text on quantum mechanics. eg “Quantum Mechanics 2nd edition, Bransden, Joachain” page: 37 and 38. To avoid any ambiguity, Its the S-G experiment which evidences space quantization (of both spin and orbital angular momentum). But Zeeman effect evidences electron spin only. It was the anomalous Zeeman effect which had led to the discovery of electron spin.

zeeman

There are also two NAT type questions which seems to be way off in the correct responses as per the exam conducting body. But the calculations shows somebody missed something somewhere. They are questions 48 and 49 according to the uploaded answer sheet and question paper. I have performed the detailed calculations in this pdf file:  gatephysics_2018.

Altogether this is 6 marks and 2/3 marks for the Q3 and Q8 if they have been deducted wrongly. So, 6+2/3 marks. I haven’t been able to find any more lapses although it was very tempting to feel so.

Wrong question in GATE 2018 physics? 1

Gate Physics 2018: Parity of vectors.

I think the above question asked in GATE 2018 (physics) is wrong.

Any vector has two components. The component perpendicular to the parity axis has even parity and the parallel component to the axis has odd parity.

The opposite is true for axial vectors.

E, A vectors.
B, L axial vectors.

The correct answer per gate exam body is E, A. Why not B and L? It’s an arbitrary situation and perpendicular components of these fields will have odd parity.

So the question since it does not specify the direction might be wrong. Unless I’m missing anything. What’s your idea ?

I am adding one relevant page for why the answer might be wrong. (A question is wrong, when all possible answers given are, wrong. That seems to be the case here.) For detailed answer and any other relevant page, check here. [Prof. S. Errede’s handouts. UIUC]

According to this lecture note from a famous university (UIUC) among E, B, L and A except L all others have odd parity. L doesn’t as its made from cross product of two vectors (r and p) which both have odd parity. There are several ways to see why B has odd parity as well. One is to see it as B = curl A. A has odd parity and grad operator has even parity. Check page 5 of the linked note from UIUC.

 

So except L all others have odd parity. [E, B and A]. Putting the phrase “only” makes the question erroneous. Because e and A pair is right but its not the only ones among the given vectors which has odd parity.

parity

 

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

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) twice every year. [Science NET is known as CSIR-NET and arts/humanities as UGC-NET.]

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

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 B (20 questions in total) try as many as you would like, to comply with your target. eg if your target is 110/200 you already got 22. So lets say you think you can score 35 in sec B (10 questions right, no negative) then you have 57 by now. So rest 53 must come from sec C, which is about 11 questions right, without negative scoring. You can vary between sec B and C to fulfill a particular target.

You should take mock tests frequently. Take a previous year question paper, set yourself 3 exam like hours without disturbance and attempt the paper. Now analyse your responses, based on the answer sheet. This way you can gauge yourself properly.

Once you have solved 5 sets of question papers, you know exactly what to be expected in the exam. eg exactly what kind of quantum mechanics questions and so on.

Brush up your concepts thoroughly based on this, from good quality texts. I will give you selection of text books, in the end. Also try to solve good number of questions from these texts. When studying the text focus on the text, not necessarily on exam. So test your understanding based on chapter-end questions. Solve them yourself. If you can’t try to find if solution manual is available. Some texts have answers available, full solutions that is.

Do proper time management, eg skip difficult or lengthy answer type questions for 2nd round. First attempt what you can solve quickly. Here by attempt I mean actually solving the question and not just selecting any choice. Also attempt first, questions, where you are thoroughly prepared. Then go to what you think you can do but requires long amount of time. Then go to attempt what you might think you may not solve but give a shot. Now review your answers for any possible mistakes.

When using scribble pad make each question have a separate space, so you can easily review later, you can leave some space to each questions space, so you can add some calculations during review.

Now go onto solve more and more questions from good study materials. Not necessarily coaching materials. It could be Schaum’s series or a good text book. Keep on taking mock tests to gauge your preparedness and requirements.

Here are some text books to follow, they are my favorite and most of them are quite helpful from NET prospective as well.

A. Mathematical Physics: 1. Mary L. Boas. 2. Riley Hobson.

B. Classical Mechanics: 1. Takwale Puranik, 2. Rana, Joag. 3. Mathur 4. Gupta (the latter two include properties of matter and wave etc)

C. Modern Physics: 1. (one stop) Arthur Beiser. 2. Eisberg and Resnick (book name: quantum mechanics of atoms molecules etc)

D. Electromagnetic Theory 1. Hecht (optics book) 2. Griffith (Ed book) 3. Berkley series (author: Purcell) 4. Mahajan Choudhury (Ed text)

E. Solid State Physics 1. Ali Omar 2. Kittel 3. Beiser (mod physics text)

F. Nuclear Physics 1. Kenneth S. Krane 2. Cohen 3. Prasad 4. Gupta

G. Electronics, Digital electronics 1. author Malvino, Leach, Saha 2. RS Sedha (S. Chand) Analog electronics; 1. VK Mehta 2. Malvino Bates 3 Tayal and Tyagi

H. Quantum Mechanics: Griffith 2. Levi (applied quantum mechanics) 3. Joachain (Pearson)

I. Statistical Mechanics 1. Reif (Berkley physics course, A must for everyone) 2. Pathria Beale (Advanced level, but thoroughly descriptive)

J. Thermodynamics 1. Garg Bansal 2. Zeemansky Dittman 3. University physics (Sears, Zeemansky et al)

You can see/refer difficult texts like Arfken, Jackson or Goldstein on a need basis.

Relativity; follow that thin book Resnick and Arthur Beiser would also help.

I hope that helps.

My analysis of Odisha elections-2017 Reply

The concurrent election in Odisha just drew to a close and I did an analysis on the results available tentatively. Notice that there is no visible errors here even if I eg adjusted 854 to 850 and so on. If you add up the % figures they add to 100% perfectly — I simply did the calculation and applied no tricks, that means there is some simple pattern in the data which is the reason I made this post. More…

A c++ code for calculating pi value. Reply

Finally I am successful in calculating pi value — less than 0.3% error, by using random number generation. Although my computer needs some fixation on its compiler or path definition etc, there are very good online compilers which helps in testing and running c++ codes: try the given link.

OUTPUT
Computing the value of pi using std::rand()
Enter number of trials: 10000
Enter number of random (x,y) points per trial: 10
pi = 3.14376 +- 0.00519107
average – exact = 0.00216735
CPU time = 0.004027 secs

Here is the code I found by searching a good deal on the web. Yes I did tinker around but only because my own compiler (Turbo C++ on windows 10, 64 bits) was throwing some exceptions on the included headers.

#include
#include
#include
#include
//#include
using namespace std;

double pi_estimate(const unsigned long points) More…