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.


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.


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.



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.

April 16. Reply

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”. More…

Interference by wave-front and amplitude splitting. Reply

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

“Color of thin films, Newton’s rings, Lloyd’s mirror and Phase changes during reflection” These lecture were delivered on 16th February, 21st February and on 17th March. The lecture sessions were of 1 and 1/2 hours. The lectures were delivered to both Physics honors as well as Physics elective students on different days.

We have previously discussed what is interference and what is wave-front splitting and amplitude splitting interference. We have also discussed in much details two wave-front splitting interference viz. Young’s double slit interference (Lecture – IX) and Fresnel’s bi-prism (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. More…