AMIETE – ET (NEW SCHEME) – Code: AE58
Subject: MATERIALS & PROCESSES
Time: 3
Hours
Max. Marks: 100
NOTE: There are 9 Questions in all.
· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.
· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.
· Any required data not explicitly given, may be suitably assumed and stated.
Q.1 Choose
the correct or the best alternative in the following: (2
10)
a. The space lattices with two lattice parameters do not belong to the system of crystals in the given shape:
(A) Tetragonal (B) Rhombohedral
(C) Hexagonal (D) Triclinic
b.
The first S value on the powder pattern of an FCC crystal (a=4.05A°) taken with
a camera of radius 57.3 mm using cobalt 
radiation of 1.79 A° is :
(A) 45 mm (B) 51 mm
(C) 72.8 mm (D) 90 mm
c. Hydrogen bonds are stronger than which of the following bonds:
(A) Vander Waal’s bonds (B) Metallic bonds
(C) Ionic bonds (D) Covalent bonds
d. The factors that promote non-crystallinity in polymers are :
(A) Number and kind of nearest neighbours
(B) Closer packing in the crystal
(C) Large random size groups
(D) None of the above
e. Which statement is correct?
(A) Ohm’s law applies to conductors only
(B) Ohm’s law applies to conductors and semiconductors only
(C) Ohm’s law applies to all materials
(D) Ohm’s law applies to superconductor and semiconductor
f. The polarisation in a dielectric is
(A) the bound charge per unit area of the dielectric
(B) the bound charge per unit volume of the dielectric
(C) the free charge per unit volume of the dielectric
(D) the free charge per unit area of the dielectric
g. The Curie temperature is the temperature at which
(A) the atomic magnetic moment disappears
(B) the domains become entirely randomly magnetized
(C) the saturation intensity of magnetization becomes infinite
(D) the saturation intensity of magnetization becomes zero
h. In a p-n junction there is a charge difference across the depletion layer, due to the fixed impurity ions such that
(A) the p-side is negative and the n-side is positive
(B) the p-side is positive and the n-side is negative
(C) both sides are positive but the n-side has the bigger positive charge
(D) both sides are positive but the p-side has the bigger positive charge
i. Which statement is correct?
(A) An insulator has a wide forbidden energy gap.
(B) In an insulator, the valence band is completely filled with electrons, and conduction band is completely empty.
(C) The upper band in an insulator contributes to electrical conductivity since no electrons are present to act as carriers
(D) It is impossible for any electron in the filled valence band of an insulator to be accelerated by an electric field.
j. High-permittivity ceramic is used for capacitor in the range of value of capacitance of:
(A) few hundred pF to many µF (B) few hundred µF to many mF
(C) few hundred mF to few F (D) none of the above
Answer any FIVE Questions out of EIGHT Questions.
Each question carries 16 marks.
Q.2 a. What are Bravais lattices and their corresponding unit cells by which their space lattices are exclusively specified? Explain all the seven crystal systems. (8)
b. Differentiate between covalent bonding, Metallic bonding and Van der Waals bonding? How does the melting & boiling points of materials vary with increasing bond strength? Explain. (8)
Q.3 a. Explain with neat diagram & suitable examples the structure of covalent solids. (6)
b. Calculate
the packing efficiency and the density of diamond. The nearest neighbour
distance between two atoms is a 
, where a is the lattice parameter.
(4)
c. What are the factors which influence:
(i) Crystallinity of long chain polymers
(ii) Surface imperfections in crystal (6)
Q.4 a. Explain superconductivity and its two applications. Why the conductivity of metals decreases with temperature whereas the conductivity of semiconductor increases with temperature? Explain qualitatively. (10)
b. What is Fermi energy? Describe the Fermi-Dirac distribution of the kinetic energy of free electrons in a metal. (6)
Q.5 a. What are different kinds of polarizabilities? Explain. How do they depend on frequency? (8)
b. Derive Claussius – Mossotti relation. How this relation would be used for the explanation of molecular structure? (8)
Q.6 a. What is the origin of ferromagnetism? Explain domain’s theory of ferro-magnetism. How is paramagnetism and diamgnetism different from ferromagnetism? (8)
b. What type of material would you recommend for permanent magnet and for high magnetic memory? Explain. (8)
Q.7 a. Describe the Hall effect and explain its relation to the mechanical force exerted by magnetic field on a conductor. A sample of n-type semi-conductor having a resistivity of 0.1 ohm-cm and a Hall coefficient of 100 cm3 / Coulomb. Assuming only electrons as carriers, determine the electron density and mobility. (8)
b. Explain the following passive materials and process materials which are used for fabrication of semi-conductor devices:
(i) Susceptor Material (ii) Device Potting
(iii) Reactor Envelopes (iv) Etchants (8)
Q.8 a. Explain the breakdown phenomenon across a barrier junction diode, clearly differentiating between the zener and avalanche breakdown phenomena. Calculate the avalanche breakdown voltage of a Germanium p-n junction where Na = Nd = 1031/m3 and relative permittivity is 16. The critical field strength is 200,000 V/cm. (8)
b. What are Relays? How are they classified on the basis of their specialised functions that they have to perform? Briefly describe Dry Reed Relay and Ferreed Relay. (8)
Q.9 a. How are FET’s different from BJT’s? Explain the construction and principle of operation of a JFET. (8)
b. Describe the Czochralski method of growing single crystal semi-conductor. Briefly describe the process of fabrication of junction transistors. (8)