Physics Optional Strategy - By prof. D.P. Vajpayee, Director DIAS

Whether Physics a Safe Optional in Cse (Mains)?

Physics is one of the most preferred optional amongst the Science/Engg stream subjects. Reasons in its favour are:

1. It’s well defined and well-structured syllabus. Horizontal and vertical spread is well defined by the syllabus.
2. It’s scoring nature. Every year lot many Physics candidates make it to “Top-100”.
3. Easy availability of study material.
4. Its reliable nature. If it has been prepared well, one can easily score up to 60-65% of marks i.e. between 300-330 marks.Value addition in every successive attempt.
5. Highest success rate of 10 % among popular optional.
6. With the same preparation many other competitions like Indian Forest Service, State PSCs, State Forest Services, UPSC Geophysicist, etc. can be successfully competed. Physics is very scoring optional for all these and many such competitions.

• In spite of all above mentioned factors, few people are creating an environment that these days Physics is not very scoring. You have to put lot of efforts to score “well” in this subject. So on and so forth. My answer to all these is that only those candidates do not score well in this subject who either leave many portions of the syllabus, do not give to-the-point answers or do not practice right way of answering the questions.
• A to Z of the present syllabus can be studied within 220 hours of study (this is the time, I take in completing the whole course). Hence allegation of requirement of lot of time is not all that correct. Successful candidates every year score 300+ Marks in this subject. Therefore Science and Engineering background candidates can safely opt for physics as their optional.

Nature of Physics Optional in Cse Mains

Now let me discuss the nature of Physics question papers in Mains examination. Like any other optional, Physics too has two papers of 250 marks each. Each paper being divided into two sections of 4 questions each. And out of these 8 questions, one has to attempt only 5. First question of both sections being compulsory, meaning there by that one has to choose remaining 3 questions out of 6. (Good 50% choice).

All questions typically have 3 bits each barring compulsory questions, where there are 5 bits of ten marks each. This is the format of the question papers. Now let’s discuss topic wise emphasis in both the papers.

Section “A” of Paper I: comprises of (i) Mechanics and (ii) Waves & Optics and in a compulsory question two bits are asked from both the courses each is asked from all the three courses and remaining bit depends on the liking of examiner, which he may ask from any one of the three courses. Therefore on an average from every course 4 bits are asked. Each bit is of 20 marks and should be answered within 12 minutes.

• Mechanics have four well defined units: Particle dynamics, System of particles (Rigid body dynamics), Mechanics of continuous media and Special Theory of Relativity. One bit is asked from each topic. Hence you should not leave any topic. This course can be well prepared from text books of classical mechanics by A.B. Gupta/J.C. Upadhyay. For supplementary reading, Mechanics by Kleppner and Kolenkov can be consulted.
• From Special Relativity, at the most two bits may be asked. Hence all old topics like Lorentz transformations, Length contraction, time dilation, velocity addition, Mass-Energy equivalence are important. New additions like Minkowski world, covariance, etc. are also important. This topic may be prepared from Special Relativity by Rebert Resnick/Gupta & Goyal.
• In Waves, damped and forced oscillations, phase and group velocity should be given due importance. This portion can be prepared from any book because all topics are very common and given in all text books.
• In Geometrical optics, Fermat’s principle and matrix method should be prepared well. Geometrical optics along with Physical optics can be prepared from book on optics by Prof. Ajay Ghatak. Physical optics also has three well defined topics providing one bit each. In interference, division of amplitude class should be prepared well, and in modern optics, optical fibres, spatial and temporal coherence and lasers be given due weightage.

Section B of Paper I: comprises of (i) Electricity & Magnetism which included portions of E.M. theory and Black Body radiation and (ii) Thermal and statistical physics.

• Format of this section is same as section A i.e. one question each from all the three courses and one bit from each course makes the compulsory question. Courses of electricity and magnetism have two well defined topics of electrostatics/ magnetostatics and current electricity. This course, along with EM theory has been very straight forward and quite scoring. Thermal and statistical Physics can be prepared from textbook by Garg, Bansal & Ghosh. Ideal Fermi systems, adiabatic demagnetization, etc. should be given due attention.

Paper- II: Second paper of Physics can be very well covered in 90-100 hours and therefore, if prepared well, can fetch rich dividends. Section A of paper II consists of Quantum Mechanics and Spectroscopy, while section “B” has Nuclear & Particle Physics and Electronics & Solid State Physics.

• Whole of the second paper excluding electronics can be prepared from Quantum Physics by Resnick and Eisberg/ Modern Physics by Arthur Beiser. Above books can be supplemented by Quantum Mechanics by David Griffiths/HC Verma, Atomic Spectra by White, Molecular Spectra by Banwell, Rajkumar, and Nuclear Physics by DC Tayal. Electronics can be prepared from text book by Allan Mottershed/ B. L. Thareja Vol. 4 and for Solid State Physics; text book by Kittel/ Puri & Babbar can be used.
• In Nuclear Physics, semi-empirical mass formula, deuteron problem, Shell model of nucleus and theory of β-decay should be prepared well.
• With the latest revision of syllabus, syllabus of electronics has been enhanced and questions have also been asked from this new portion of JFET, MOSFET and fundamentals of microprocessors. Among the courses of Paper II, electronics has maximum syllabus. Therefore non-electronics background candidates should make some extra efforts to master this part of syllabus or may also omit it.

Some General Tips

1. My first advice is that one should not skip any portion of the syllabus. Thorough study is a must to get 300+marks. Nothing must be omitted from both the papers.
2. Analyse the examination papers of previous few years. You’ll know yourself where the focus is. For this you may use our topic wise collection of CSE questions, we call them Tutorial Sheets. One may download them from our website diasindia.com
3. Take practice tests and get them evaluated by a teacher and see yourself, what improvements can be made.
4. While taking the exams, read the questions correctly and carefully. Your answers should be to the point; beating about the bush only wastes your time and doesn’t fetch any extra mark. Units and terms used in formulas should be clearly explained. If a question deals with ‘what’ and ‘how’, you must definitely incorporate ‘why’ and one line concluding remark answering where i.e. its relevance or application.
5. Do not give the derivation if it has not been asked. I’ll elaborate on this point, with the help of a problem asked in 2019’s exam. “Write down Euler’s equation of motion of a rigid body about a fixed point under the action of a torque show that the kinetic energy of a torque free motion is constant". In this question, you are supposed to write general Euler's equation, clearly explaining all the terms and frame of reference and by taking torque zero. Show desired result and interpret quantities. Here there is no need to derive an equation. Apart from mentioning torque is the cause change in angular momentum is the effect and expressed in the body set, it is Euler’s equation. Answering "why" in every question of Physics is must.
6. Finally one must stay ‘cool’ during the examination. Do not get panicky, even if you do not know few things.

Recommended Books

Before recommending any book, let me tell you my oft repeated mantra: “Every book and every teacher is equally good". Their job is only to present the experimentally verified facts (called theories) and to illustrate those basic concepts by giving some illustrations. Only illustration and style of presentation may differ from teacher to teacher and book to book. Success of a teacher is typically measured in terms of success of their students.

• So if by studying from a particular book or a teacher, one succeeds, then that book starts trending and becomes popular. For Physics, I have recommended two sets of books, one is by internationally acclaimed writers, which typically are error free and have been widely used over space and time and second set of books by Indian writers, which have large number of solved problems, but may or may not have desired theoretical depth. In this list I have tried to be as objective as possible, but cannot be called free from personal biases and preferences due to human nature.

Paper I

• Mechanics: Klappner & Kolenkov / AB Gupta / JC Upadhyay
• Waves & Optics: Jenkins and White/ Ajay Ghatak /Brijlal , Subramanyam and Avdhesanulu
• Electrodynamics & EM Theory: David Griffiths /Chopra & Agrwal/ Satya Prakash
• Thermal & Statistical Physics: Zemansky & Dittman /Garg, Bansal & Ghosh / Satya Prakash & Agrawal

Paper II

• Quantum Physics: Resnick & Eisberg
• Concepts of Modern Physics: Arthur Beiser
• Quantum Mechanics: David Griffiths/ HC Verma / Satya Prakash
• Atomic & Molecular Spectra: Raj Kumar
• Molecular Physics: Banwell
• Nuclear Physics: DC Tayal
• Solid State Physics: Kittel /Puri & Babbar
• Electronics: Allan Mottershed/ B L Thareja Vol. IV