UPSC Physics Optional PYQs (CSE & IFoS)PYQs

Describe the phenomenon of Meissner effect and its importance in the study of superconductors.

Give schematic diagrams to distinguish between n\text{-}p\text{-}n and p\text{-}n\text{-}p transistors.

What is the difference between direct and indirect band gap semiconductors? Which one is suitable for use in solar cells?

With the help of a schematic diagram, show how entropy and specific heat vary with temperature for a superconductor.

The primitive translation vectors of a two-dimensional lattice are \hat{a}=2\hat{i}+\hat{j},\quad \hat{b}=2\hat{j}. Determine the primitive translation vectors of its reciprocal lattice.

Obtain Laue's equations for X-ray diffraction by crystals. Show that these are consistent with the Bragg's law.

Obtain the Q-values for the following four nuclear reactions :

(i) {}^{14}_{7}\text{N} + ^{4}_{2}\text{He} \rightarrow ^{17}_{8}\text{O} + ^{1}_{1}\text{H}

(ii) {}^{7}_{3}\text{Li} + ^{4}_{2}\text{He} \rightarrow ^{10}_{5}\text{B} + ^{1}_{0}\text{n}

(iii) {}^{6}_{3}\text{Li} + ^{1}_{1}\text{H} \rightarrow ^{3}_{2}\text{He} + ^{4}_{2}\text{He}

(iv) {}^{23}_{11}\text{Na} + ^{1}_{1}\text{H} \rightarrow ^{20}_{10}\text{Ne} + ^{4}_{2}\text{He}

In a nuclear fusion process, four hydrogen nuclei combine to form a helium nucleus. Obtain the energy released in such a process. If the same process is responsible for energy of a star of mass 2 \times 10^{30}\text{ kg}, each kilogram having 6 \times 10^{26} protons, what could be the magnitude of energy released in it?

What are elementary particles and how are they classified? Describe in brief the different types of interactions that can occur between the elementary particles.

Explain the various leptonic family members. What is leptonic number conservation? Based on this conservation law, state whether the following reactions are possible or not:

(i) \pi^- \to \mu^- \bar{\nu}_\tau

(ii) n \to p + e^- \bar{\nu}_e

Predict the spin and parity of ground states of the following nuclei on the basis of shell model:

(i) {}_{8}\mathrm{O}^{15}

(ii) {}_{8}\mathrm{O}^{16}

(iii) {}_{17}\mathrm{Cl}^{38}

Write down the quark structure of the following hadrons: \Delta^{++}, \Omega^-, \Sigma^- and \Lambda^0 Write down the following decays in terms of quarks:

(i) n \to p + e^- \bar{\nu}_e

(ii) \Delta^+ \to \pi^+ + n

(iii) \Sigma^+ \to p + \pi^0

State the basic assumption of single particle shell model. How do the centrifugal and spin-orbit terms remove the degeneracy of a three-dimensional spherical harmonic oscillator?

Explain unification of electromagnetic and weak interactions. What is Z^0-boson? What is its relevance in electroweak unification?

Show that in the nuclear shell model, the level spacing between major oscillator shells is approximately \hbar\omega = 41\,A^{-1/3}\,\mathrm{MeV}.

What is parity transformation? Discuss the experiment that confirms the violation of parity in beta decay.

What are leptons? How are they different from other baryons? Define their quantum numbers and identify the forbidden ones in the following scattering or decay processes, justifying your conclusions :

(i) \pi^0 \rightarrow \gamma + \gamma

(ii) \pi^0 \rightarrow \gamma + \gamma \rightarrow (e^+ + e^-) + (\mu^- + \mu^+)

(iii) n \rightarrow p + e^- + \bar{\nu}_\mu

(iv) \pi^+ + p \rightarrow p + p + u_\tau + \bar{\nu}_e

(v) u_e + p \rightarrow u_\mu + p + \pi^0

Give an outline of meson theory of nuclear forces. Describe the physical basis of short-range nuclear repulsion between like nucleons : proton-proton (p\text{-}p) or neutron-neutron (n\text{-}n). Consider the following two three-nucleon systems : (p\text{-}p\text{-}p) and (n\text{-}n\text{-}n). Which one is more likely to form a bound state?

Describe the properties of field quanta of electro-weak and strong interactions of particles.

Explain why the deuteron has no excited state.