Jawaharlal Nehru Technological University, Hyderabad
Jawaharlal Nehru Technological University, Hyderabad B.Tech I Year ENGINEERING PHYSICS Previous Question Paper (September/October - 2021 - R15)
Answer any five questions. All questions carry equal marks.
Main
Define basis, lattice parameters, unit cell.
Answer
Basis: A basis is a group of one or more atoms (or molecules) associated with each lattice point. When the basis is placed at every lattice point, the actual crystal structure is formed.
Lattice parameters: These are the dimensions that define the geometry of a unit cell. They consist of the three edge lengths (a, b, c) along the crystallographic axes and the three interfacial angles (α, β, γ) between these axes.
Unit cell: A unit cell is the smallest repeating structural unit that, when translated in three dimensions, generates the entire crystal lattice. It represents the symmetry and properties of the entire crystal.
Describe seven crystal systems and their corresponding Bravais lattices.
Answer
Crystals are classified into seven systems based on their lattice parameters. These systems, combined with different centering types (Primitive P, Body-centered I, Face-centered F, and Base-centered C), result in 14 Bravais lattices.
| Crystal System | Axial Lengths | Interfacial Angles | Bravais Lattices |
|---|---|---|---|
| Cubic | a=b=c | α=β=γ=90° | P, I, F |
| Tetragonal | a=b≠c | α=β=γ=90° | P, I |
| Orthorhombic | a≠b≠c | α=β=γ=90° | P, I, F, C |
| Rhombohedral | a=b=c | α=β=γ≠90° | P |
| Hexagonal | a=b≠c | α=β=90°, γ=120° | P |
| Monoclinic | a≠b≠c | α=γ=90°≠β | P, C |
| Triclinic | a≠b≠c | α≠β≠γ≠90° | P |
Explain bonding in solids briefly.
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Derive an expression for cohesive energy of general solids.
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Compare the properties of waves and particles.
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Derive an expression for energy of a particle in an infinite potential well.
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State and explain about Heisenberg’s uncertainty principle.
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Define Fermi level and derive an expression for Fermi energy.
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Compare Maxwell-Boltzmann, Bose-Einstein and Fermi-Dirac statistics.
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Obtain expression for internal fields in the solids.
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Discuss about ferro-electricity in magnetic materials.
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The dielectric constant of helium gas at NTP is 1.0000684. Calculate the electronic polarisability of helium atoms if the gas contains 2.7 × 1025 atoms/m3.
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Define the terms permeability, magnetic moment and magnetic field induction.
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Explain origin of magnetic moment and based on magnetic moment explain the classification of magnetic materials.
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Compare and contrast soft and hard magnetic materials.
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Explain superposition of waves.
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Compare and contrast Fresnel and Fraunhofer diffractions.
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Derive an expression for interference in thin films by reflection.
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Obtain an expression of Sabine’s formula for reverberation time.
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Define phenomena of reverberation and reverberation time.
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A hall has a volume of 2500 m3. Its total absorption is equivalent to 100 m2 of open windows. If the hall is filled with audience who add another 80 m2 of open window, then what is the effect on the reverberation time?
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