Physics 2022 Paper II 50 marks Compulsory Explain

Q5

(a) If the nuclear force is charge independent and a neutron and proton form a bound state then why is there no bound state for two neutrons ? What information does this provide on the nucleon-nucleon force ? (10 marks) (b) Explain why each of the following particles cannot exist according to the quark model. (i) A Baryon of spin 1 and (ii) An anti-Baryon of electric charge +2 (10 marks) (c) Explain why Type-II superconductor is better than Type-I superconductor in the application of superconductor magnets. (10 marks) (d) Why is the Field Effect Transistor (FET) called Unipolar Transistor ? Discuss how it is superior than Bipolar Junction Transistor. (10 marks) (e) Why NAND and NOR gates are called universal gates ? Give the logic diagram, Boolean equation and the truth table of a X-OR gate. (10 marks)

हिंदी में प्रश्न पढ़ें

(a) यदि नाभिकीय बल आवेश से स्वतंत्र है और एक न्यूट्रॉन और एक प्रोटॉन बाध्य अवस्था बनाते हैं तो दो न्यूट्रॉनों के लिए बाध्य अवस्था क्यों नहीं है ? यह न्यूक्लिऑन-न्यूक्लिऑन बल पर क्या जानकारी प्रदान करता है ? (10 अंक) (b) स्पष्ट कीजिए कि इनमें से प्रत्येक कण क्वार्क-मॉडल के अनुसार क्यों विद्यमान नहीं हो सकता । (i) 1 स्पिन (प्रचक्रण) का एक बेरियन एवं (ii) विद्युत आवेश +2 का एक एंटी-बेरियन (10 अंक) (c) व्याख्या कीजिए कि क्यों अतिचालक चुंबकों के अनुप्रयोग में टाइप-II अतिचालक टाइप-I अतिचालक से बेहतर होता है। (10 अंक) (d) क्षेत्र प्रभाव ट्रांजिस्टर (फेट) को क्यों एक ध्रुवी ट्रांजिस्टर कहा जाता है ? कैसे यह द्विध्रुवी संधि ट्रांजिस्टर से श्रेष्ठ है, व्याख्या कीजिए। (10 अंक) (e) NAND और NOR गेट्स को सार्वभौमिक गेट्स क्यों कहा जाता है ? X-OR गेट का तर्क-आरेख, बूलियन समीकरण, और सत्य-टेबल दीजिए। (10 अंक)

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Directive word: Explain

This question asks you to explain. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

The directive 'explain' demands clear causal reasoning and mechanistic understanding across all sub-parts. Allocate approximately 20% time each to (a), (b), (c), (d), and (e) as all carry equal marks. Structure with brief introductions for each sub-part, followed by systematic causal explanations, and conclude with synthesizing remarks on nuclear forces, quark confinement, and device applications. For (b)(i)-(ii), treat both as mandatory; for (e), ensure all three components (NAND/NOR universality, XOR diagram, Boolean equation, truth table) are addressed.

Key points expected

  • (a) Explains why dineutron is unbound despite charge-independent nuclear force: Pauli exclusion principle forbids identical fermions in same state, so nn system must be in spin-triplet (antisymmetric space) with reduced overlap vs deuteron's spin-singlet; cites tensor force and spin-dependence of nuclear force
  • (b)(i) Demonstrates baryon spin-1 impossibility: three quarks (spin-1/2 each) can only combine to total spin 1/2 or 3/2 via angular momentum coupling, never spin-1; shows explicit quark spin wavefunction construction
  • (b)(ii) Proves anti-baryon charge +2 impossibility: anti-baryon has three antiquarks, each with charge +1/3 or +2/3, giving maximum possible charge +2 only if all three are anti-up (+2/3 each), but this violates color singlet requirement (antisymmetric color × antisymmetric flavor × symmetric spin)
  • (c) Contrasts Type-I (complete Meissner effect, H < Hc) vs Type-II (vortex state, Hc1 < H < Hc2): explains flux penetration via Abrikosov vortices, higher critical fields enabling superconducting magnets; mentions Indian contributions (K. S. Novoselov's graphene work context, or indigenous superconductor research at BARC/IITs)
  • (d) Defines FET as unipolar (single carrier type: electrons in n-channel or holes in p-channel) vs BJT (bipolar: both carriers); lists superiority: high input impedance, voltage-controlled, negligible gate current, thermal stability, smaller size, faster switching; mentions Indian semiconductor initiatives (ISRO's indigenous fabrication)
  • (e) Proves NAND/NOR universality by constructing NOT, AND, OR from each; provides complete XOR: logic diagram with NAND gates, Boolean expression Y = A⊕B = A'B + AB' = (A+B)(A'+B'), truth table with all four input combinations

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Accurately identifies Pauli principle for dineutron instability; correctly applies SU(6) quark model spin/flavor/color constraints for (b); precisely distinguishes Type-I/II superconductivity mechanisms; correctly defines unipolar operation and FET advantages; flawlessly demonstrates NAND/NOR universality with correct XOR implementationIdentifies some correct concepts but confuses spin-statistics for (a), or misstates quark charges for (b), or conflates critical fields for (c), or lists FET properties without clear unipolar explanation, or shows incomplete XOR derivationFundamental misconceptions: claims nuclear force is charge-dependent for (a), or allows spin-1 baryon, or permits +2 anti-baryon; confuses superconductor types; describes FET as bipolar; fails to show universality or provides incorrect truth table
Derivation rigour20%10Shows explicit angular momentum coupling for quark spins in (b)(i); derives charge constraints from antiquark content in (b)(ii); presents H-T phase diagram boundary derivations for Type-II; systematically derives XOR from universal gates with Boolean algebra stepsStates correct results with partial derivations; mentions but doesn't fully develop spin coupling rules; outlines but doesn't complete Boolean simplification for XOR; presents phase boundaries without derivationNo derivations attempted; asserts conclusions without justification; incorrect or missing Boolean algebra; confuses derivations across sub-parts
Diagram / FBD20%10Clear H-T phase diagrams showing Meissner, vortex, and normal states for Type-I and Type-II with Hc1, Hc2 marked; neat XOR logic diagram using NAND/NOR gates with proper gate symbols; well-labeled FET structure showing channel formationBasic phase diagram without clear region labels; functional XOR diagram with minor symbol errors; simple FET sketch without bias configurationMissing or incorrect diagrams; confused Type-I/II representations; unrecognizable logic symbols; no FET structure shown
Numerical accuracy15%7.5Correct quark charge values (+2/3, -1/3) and antiquark charges; accurate spin quantum numbers (1/2, 3/2); correct truth table values (0,1) for all XOR combinations; proper critical field ratios if mentionedMinor numerical errors in one sub-part; mostly correct values with occasional sign errorsSystematic numerical errors: wrong quark charges, incorrect spin values, wrong truth table outputs
Physical interpretation20%10Connects dineutron instability to deuteron binding and nuclear force spin-dependence; relates quark model constraints to observable hadron spectrum; explains why Type-II vortex state enables high-field magnets (MRI, NMR, fusion); interprets FET advantages for low-power digital circuits; discusses NAND universality in modern VLSI designSome connections made between concepts and applications but lacks depth; mentions applications without explaining physical basisNo physical interpretation provided; purely descriptive without explanatory depth; irrelevant or incorrect applications cited

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