Attempt any FIVE.

1(a)
Explain term lattice parameters of cubic crystal.

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1(b)
What is the probability of an electron being thermally excited to conduction band in silicon at 20

^{o}C. The band gap energy is 1.12eV; Boltzmann constant is 1.38 x 10^{-23}JIk.
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1(c)
Mobility of holes is 0.025 m

^{2}/V-sec What would be the resistivity of P-type silicon . if the Hall coefficient of the sample is 2.25 x 10^{-5}m^{3}/C ?
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1(d)
Define dielectrics, electric dipole, polarizability.

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1(e)
Difference between soft and hard magnetic materials

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1(f)
Define Reverberation time. Write Sabine's formula and explain terms in it.

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1(g)
State the terms : magnetostriction effect; piezoelectric effect

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2(a)
Explain the formation of energy band in solids. With neat energy band diagram explain extrinsic semiconductors.

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2(b)
Draw the unit cell of HCP. What is its co-ordination number, atomic radius, effective number of atoms per unit cell. Also calculate its packing factor .

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3(a)
What is hysteresis? Draw a hysteris loop for ferromagnetic material and explain the various important points on it. What is the technical significance of the area enclosed under it. For a transformer which kind of material will you prefer-the one with small hysteresis area or the big one ?

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3(b)
Derive Bragg's law. Calculate the glancing angle on the plane (100) for a crystal of rock salt (a = 2.125 A

^{0}.Consider the case of 2nd order maximum and A = 0.592 A^{0}.
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4(a)
Calculate the number of atoms per unit cell of a metal having lattice parameter 2.9A

^{0}and density 7.87 gm/cm3. Atomic weight of metal is 55.85, Avagadro number is 6.023 x 10^{23}/gm-mole.
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4(b)
Prove that the Fermi level lies exactly at the centre of the forbidden energy gap in case of an intrinsic semiconductor.

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4(c)
Explain ionic polarization and obtain polarizability.

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5(a)
With neat diagram of a unit cell, explain the structure of BaTi0

_{3}.
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5(b)
What is Hall effect ? Derive expression for Hall voltage.

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5(c)
Explain the absorption coeficient of a hall. Calculate the change in intensity level if the intensity of sound increases 1000 times its original intensity.

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6(a)
In what sense real crystals differ from ideal crystals? Explain the point defects in crystals.

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6(b)
Explain construction and working of a solar cell.

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6(c)
Find the natural frequency of vibration of quartz plate of thickness 2mm. Given Young's 5 modulus of quartz Y = 8 x 10

^{10}N/m^{2}, density of quartz is 2650 kg/m^{3}. Calculate the change in thickness required if the same plate is used to produce ultrasonic waves of frequency 3MHz.
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