Physics is an optional subject offered by the UPSC in the mains exam. It is a core science subject and one that can be safely opted only by graduates of physics or engineering. It must be said that although the overlap with the General Studies papers is virtually zero, physics can be a scoring subject if thoroughly and systematically prepared. In this article, we discuss all you need to know regarding the physics optional – toppers, optional success rate, strategy, preparation tips, booklist, etc.
How many take Physics optional?
Not many take physics as their optional in the IAS mains exam. This is owing to the nature of the subject, no doubt. Nevertheless, there have been toppers who with this optional were able to notch up their final scores and get a high rank. The following table shows the success rates of physics optional from 2010 to 2015.
Physics optional success rate:
|Year||No. of candidates appeared||No. of candidates cleared||Success rate (%)|
IAS toppers with physics optional
There have been toppers with this optional, the most recent being Abhishek Surana, who bagged the tenth rank in the 2017 UPSC exam.
Take a look at the next table which gives the names of a few toppers with physics optional.
Physics optional pros and cons
There are both positives and negatives to taking physics as your optional in the IAS mains exam. In this section, we discuss both the pros and cons. If you are undecided on your optional, you should assess these pros and cons, evaluate your own strengths and weaknesses and then come to a decision.
Physics optional pros
- Being a scientific and rational subject, there is no scope for interpretation here. If you write the answer correctly, you should get marks as nothing is subjective.
- It is a scoring subject as you can score marks with diagrams and pictorial representations. There are also numericals here which when done correctly can fetch you maximum marks.
- If you have a solid base in this subject, you must definitely go for this optional as you can score good marks in the two optional papers and up your final tally in the UPSC exam.
- The overlap is minimal, although in certain science and technology topics, you can write brilliant answers with your base in physics.
- Competition is far less than what you would encounter in subjects like geography and public administration.
- The most remarkable thing about this optional (and indeed, any core science optional) is that you can predict how well you did in the papers unlike in the humanities subjects.
- If you cover the syllabus entirely, you can easily answer 80% of the question paper.
- The physics optional syllabus is largely static and the pattern in pretty much set.
Physics optional cons
- The overlap with GS papers is minimal.
- Absolute conceptual clarity is needed to write good answers in this subject. Tackling numericals also require a solid understanding of the theory behind them, and also ample practice.
- You have to write precise answers as it is a core science subject. You cannot beat around the bush in any answer and hope to get minimum marks.
- Ample revision is required in this optional. You have to practice and revise on a daily basis if you want to be able to perform well.
- Only those candidates with physics or engineering backgrounds can take this optional.
Physics optional syllabus
Let us take a look at the syllabus for physics for the UPSC mains exam.
There are two optional papers in the UPSC exam pattern. Both the papers are for a total of 250 marks making the total optional marks to 500.
Download the Physics syllabus PDF.
Physics optional strategy
General tips for physics optional in UPSC:
- Writing practice is absolutely essential in this subject. Practice past UPSC question papers. This will also give you a sense of the important and repeated areas from where questions are asked in the mains exam.
- In numericals, you must write the theory also behind the problem. Only this will fetch you maximum marks. Only solving the numerical is not sufficient. Again, understand what is to be written and what is to be avoided according to the marks allotted to that question.
- In any question, talk about the underlying physical phenomenon as well as the mathematical solution to it.
- Diagrams must be relevant, neat and correctly labelled.
- It is advisable to make your own notes in this subject. As the reading material would be scattered and from various books and sources, making notes would make revision convenient and less time-consuming.
- Practise is key in this optional. You must practice the derivations and numericals multiple times to be able to reproduce them in the answer booklet with ease.
- Try to make your answers better than the rest by drawing neat diagrams and presenting it in a good way. For example, derivations are always the same and everyone writes them in the same way. Here, you can make your answers stand out by presenting a good background theory, writing in a good legible hand and giving good pictorial representations of the same.
- Solving previous years papers is very important because at least 70% of the questions are repeated from previous years in this optional.
- Have separate notes for formulas only. For each unit, have a list of formulas. This will come in handy during revision. They help in solving numericals faster. These formulas have to be mugged up to save time in the exam. There is no way around them.
- Another important point to remember is not to write what is not asked in the exam. Apart from being a waste of time, it can also backfire and the examiner may cut marks for writing unnecessary things.
- If you can, do join a test series for physics optional. They will give you exposure to exam-simulation. You will learn time management and also understand where you stand and course-correct your preparation if needed. This exercise will also give you much-needed confidence.
- Be accurate in your answers especially numericals. Because if you get the incorrect answer, you lose marks and this can make a difference of 20 to 30 marks which can hamper your UPSC attempt. Hence, accuracy is extremely important and you can develop it only by practice.
- Complete the entire syllabus. It is not advisable to leave any topic. For instance, in 2015, two questions were asked on optics each for 20 marks. So, any aspirant who had left that chapter would have not been able to do well.
Physics paper I strategy
- Mechanics of Particles – the best book for this section is ‘Fundamentals of Mechanics’ by JC Upadhyaya. Alternatively, you can also use ‘Mechanics’ by DS Mathur. Either one book will do. But remember in this optional, book reading is essential. Only class notes (if you are attending coaching) will not suffice.
Q. Use Gauss’s theorem to calculate the gravitational potential due to a solid sphere at a point outside the sphere. Calculate the amount of work required to send a body of mass m from the Earth’s surface to a height R/2, where R is the radius of the Earth. (15 marks, 2018)
Q. Describe Michelson-Morley experiment and show how the negative results obtained from this experiment were interpreted. (10 marks, 2017)
Q. Define the moment of inertia and explain its physical significance. Calculate the moment of inertia of an annular ring about an axis passing through its centre and perpendicular to its plane. (20 marks, 2017)
- Waves and Optics – ‘Optics’ by Ajoy Ghatak is a very important book for this section. The examples from this book are being asked directly by the UPSC. So, it is very important to go through them. The diagrams in this book are also excellent.
Q. When the two waves of nearly equal frequencies interfere, then show that the number of beats produced per second is equal to the difference of their frequencies. (10 marks, 2018)
Q. Distinguish between positive and negative crystals in terms of double refraction. How are these crystals used to make quarter wave plates? Explain how the quarter wave plate is used in producing elliptically and circularly polarised light. (15 marks, 2018)
Q. What is multiple-beam interference? Discuss the advantages of multiple-beam interferometry over two-beam interferometry. Explain the fringes formed by Fabry-Perot interferometer. (15 marks, 2017)
- Thermodynamics – you can refer to ‘Thermal Physics’ by Garg, Bansal & Ghosh for this section. In this book also, the diagrams and examples are important.
Q. A system having two energy levels, -½ Δ and +½ Δ with Δ = 10 meV is populated by 1000 particles at a low temperature close to 100 K. Obtain the average energy per particle using classical distribution law. (15 marks, 2018)
Q. Using the Maxwell-Boltzmann distribution law, show that there cannot be any negative absolute temperature. (10 marks, 2017)
Q. Write and explain the Maxwell-Boltzmann distribution. Using this distribution, find the expressions for the most probable speed, mean speed and root-mean-square speed. (15 marks, 2017)
- Electricity and Magnetism – ‘Introduction to Electrodynamics’ by David J. Griffiths is the best book for electrodynamics.
Q. (i) What are the limitations of Rayleigh-Jeans law in explaining the spectrum of radiations from a blackbody? Explain how these limitations were overcome in Planck’s Radiation Law.
(ii) Deduce Wien’s displacement law from Planck’s radiation law. (20 marks, 2018)
Physics paper II strategy
- Quantum Mechanics – HC Verma is a good book for quantum mechanics. This is a simple book and easy to read.
Q. A beam of 4.0 keV electrons from a source is incident on a target 50 cm away. Find the radius of the electron beamspot due to Heisenberg’s Uncertainty Principle. (10 marks, 2017)
- Atomic and Molecular Physics – this is a short topic but a lot of questions are asked from here. For this section, you should literally mug up the book ‘Atomic and Molecular Physics’ by Raj Kumar. Refer to all the solved examples from this book. Another book which you can read is Banwell.
Q. What is Zeeman effect? Discuss the factors on which Larmor frequency is dependent. (15 marks, 2018)
Q. Discuss the theory of rotational and vibrational spectra of diatomic molecules. What is the difference between fluorescence and phosphorescence? (20 marks, 2018)
Q. State Franck-Condon principle. Define Franck-Condon factors. Using schematic diagram, explain the decay of excited states leading to the phenomenon of fluorescence and phosphorescence. (20 marks, 2017)
- Nuclear and Particle Physics – for this section, you must refer to multiple books as all the material is not available in one place. The books to be followed are ‘Concepts of Modern Physics’ by Arthur Beiser and Nuclear Physics by SN Ghoshal or Nuclear Physics by SB Patel.
Q. Nuclear forces are mediated by exchange of π-mesons of rest mass 140 meV. Estimate the range of nuclear forces. (10 marks, 2018)
Q. Explain the principle of Nuclear Magnetic Resonance (NMR) with the help of an energy level diagram. Give examples of nuclei which exhibit NMR. what major differences can be drawn from an NMR spectra? (20 marks, 2017)
- Solid State Physics, Devices and Electronics – for this section, you should refer to ‘Solid State Physics’ by Puri and Babbar. Experts say that the return on investment in this section dismal because this is a sort of an open-ended section in physics. The way to go about studying this section is to first complete reading the book by Puri and Babbar, i.e., whatever topics are mentioned in the syllabus. After that, go through the previous years papers and find out what questions have been asked from this section. Then, you focus on those areas only. For example, differences between p-n-p and n-p-n transistors have been asked several times.
Q. Calculate Atomic Packing Fraction (APF) for FCC and HCP structures, and show that these are the most closely packed structures. (10 marks, 2018)
Q. Derive Bragg diffraction law for X-ray diffraction. Compare Laue and Debye-Scherrer methods for crystal structure determination. (10 marks, 2018)
IAS Physics books
- Fundamentals of Mechanics by JC Upadhyaya
- Mechanics by DS Mathur
- Optics by Ajoy Ghatak
- Thermal Physics by Garg, Bansal & Ghosh
- Introduction to Electrodynamics by David J. Griffiths
- Quantum Physics by HC Verma
- Atomic and Molecular Physics by Raj Kumar
- Concepts of Modern Physics by Arthur Beiser
- Nuclear Physics by SN Ghoshal
- Nuclear Physics by SB Patel
- Solid State Physics by Puri and Babbar
- A Textbook of Sound by Khanna & Bedi
- Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles by Resnick & Eisberg
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