Biju Patnaik University of Technology 2008-4th Sem B.Tech (B Tech) , material science . - Question Paper

BPUT(B Tech) , fourth semester material science ques. paper.

Total number of printed pages -7 B. Tech

BSCC 2202

Fourth Semester Examination - 2008 MATERIAL SCIENCE

Full Marks-70 Time: 3 Hours

Answer Question No. 1 which is compulsory and any five from the rest.

The figures in the right-hand margin indicate marks.

(h = 6.626 x 10^-34Js, Mass of e = 9.1 x l(r³¹kg, e =1.6 x 10-¹⁹C, c = 3 x 10⁸ m/s, N = 6.023 x10²³, R = 8.314JK^-1/mol, k = 1.38xlO-²³J/K, h₀ = 4x10⁷, at.wt. :C = 12 amu, H = 1 amu)

1. Answer in brief :    2x10

(a) Why can not visible light produce ionic polarization ?

(b) (c) aos'j (e) }L iNnii'Hu* siarvf (g) (h) (i) (j)

Why does corrosion occur in oxygen lean area although oxygen accelerates corrosion ? Discuss various factors that affect the drift velocity. Why does conductivity of metal decrease at higher temperature ? What is Meissner effect ? A plane intercepts the crystal axes b at 0.5b, c at 0.25c. What are the miller indices if it is parallel to the third axis ? Name two elements which when added to Germanium will create holes. What is glass transition temperature ? Why is BaTi03 ferroelectric below 120C but not above it ? What is meant by population inversion ?

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2.    (a) Deduce the mathematical expression for

thermal conductivity of a conducting material.    4

(b) The density and atomic weight of a metal are 7140 kg/m³ and 65.38 amu respectively. The relaxation time is 10^_14sec at 300 K. Calculate    6

(i)    resistivity

(ii)    mobility of electrons and

(iii)    the average drift velocity when an electric field of 10V/cm is applied, (no of valence electrons = 2)

3.    (a) What is Fermi energy ? What is the

probability of finding the electron at the BSCC 2202    3    P.T.O.

Fermi energy level in a metal ? Will the probability be higher or smaller at Fermi energy level at a highertemperature ? 3

(b)    Calculate the electron velocity at Fermi energy of sodium at0K.(density=970kg/m³, at.wt.= 23)    4

(c)    Distinguish between conductor, semiconductor and insulator on the basis of band theory.    3

4. (a) There are 10¹² magnesium atoms, which replace an equal number of silicon atoms in a 10 mm³ wafer. Compare the conductivity with 10¹² aluminum atoms replacing equal number silicon atoms.    3

(b)    At an higher temperature, one of every 10¹⁰ valence electrons in intrinsic silicon is in the conduction band.

(i)    What is the conductivity ?

(ii)    What is the temperature ?

(a = 0.543nm,^a2o = 5xlo^-4mho/m⁴, no of atoms per unit cell =8) 4

(c)    In an n-type semiconductor, the Fermi energy level lies 0.3eV below the conduction band. Find the position of Fermi level if the temperature is increased to 350 K.

3

5. (a) Distinguish between hard and soft magnetic materials.    3

(b) A paramagnetic material has a magnetic field intensity of 10⁶A/m. Calculate the magnetization and flux density if susceptibility is 1.4x10³ at room temperature.

3

(c) Discuss the structure and applications of ferrites.    4

6.    (a) Differentiate between type-I and type-11

superconductors.    3

(b)    Calculate the critical magnetic field for Tin at 1,5K and 2.5K.(Tc = 3.72K, Hc(o) =

0.03 Tesla).    4

(c)    The polarisability of argon is1.8*iCT⁴⁰Fm². Calculate the dielectric constant at NTP.

3

7.    (a) What are isotactic, syndiotactic and atactic

polymers ?    3

(b) The weight average degree of polymerization for polypropylene is 15000. Calculate the weight average molecular weight. 3

(c) Discuss about glass fibre reinforced polymer composite.    4

8. (a) Discuss the phenomenon of passivity. Why are chromium steels more corrosion resistant than carbon steel ? 5

(b) What is LASER ? Discuss the mechanism of LASER action of He-Ne laser. 5

Attachment: biju-patnaik-university-of-technology-2008-b-tech-36035-1.pdf

Earning:   Approval pending.