AMIETE – ET (NEW SCHEME) – Code: AE58
Subject: MATERIAL AND 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 packing fraction
of a simple cube is ______.
(A) 0.48 (B) 0.52
(C) 0.65 (D) 0.89
b. The number of atoms per unit of
copper is _____.
(A) 4 (B) 6
(C) 8 (D) 12
c. The
number of missing neighbours of an atom on a {100}-type external surface in FCC
copper is ______.
(A) 4 (B) 3
(C) 2 (D) 0
d. The
reaction that yields two solid phases on cooling a single solid phase is called
________.
(A) eutectoid (B) peitectoid
(C) eutectic (D) congruent
e. Which
of the following is the best conductor of electricity?
(A) Tungsten. (B)
Aluminium.
(C) Copper. (D) Carbon.
f. Ferroelectric
materials are the dielectrics analogous to _________.
(A) ferromagnetic materials (B) paramagnetic
materials
(C) diamagnetic
materials (D) None of the above.
g. The transition from the ferromagnetic to the
paramagnetic state is named
after _______.
(A) Curie-Weiss (B) Curie
(C) Neel (D) Debye
h. If
a sample of germanium and a sample of silicon have the same impurity density
and are kept at room temperature
(A)
both will have equal value of resistivity
(B) both will have equal value of negative resistivity
(C) resistivity
of germanium will be higher than that of silicon
(D) resistivity of
silicon will be higher than that of germanium
i. Which of the
following materials are piezoelectric?
1. Barium titanate 2. Alumina 3. Silica 4. Cadmium
sulphide
(A) 1,2
and 4 (B) 1,3,and 4
(C) 1,2
and 3 (D) 2,3 and 4
j. FET is
advantageous in camparison with BJT because of _________.
(A) its
current controlled behavior (B) high gain bandwidth product
(C) high input
impedance (D) None of the above.
Answer any FIVE
Questions out of EIGHT Questions.
Each question
carries 16 marks.
Q.2 a. Increasing
the temperature of a semiconductor breaks covalent bonds. For each broken bond,
two electrons become free to move and transfer electrical charge. (10)
(i) What fraction of valence electrons is free
to move?
(ii) What fraction of the covalent bonds must be
broken in order that 
electrons conduct electrical charge in 50 g of
silicon?
(iii) What
fraction of the total silicon atoms must be replaced by arsenic atoms to
obtain one million electrons that are free to move in one pound of silicon?
.
b. Calculate the atomic radius in cm for the
following: (6)
(i) BCC metal with 
= 0.3294 nm and one atom
per lattice point; and
(ii) FCC metal with = 4.0862 
and one atom per lattice
point.
Q.3 a. In
a simple cubic structure there are 
of edge dislocations.
How much would each of these climb down an average when the crystal is heated
from 0 to 1000 K? The lattice parameter is 2. The volume of one mole of
the crystal is 5.5
. The enthalpy of formation of vacancies is 100 KJ/mole. (8)
b. What are the four main
generic classes of polymers? For each generic class:
give one example of a
specific component made from that class. (8)
Q.4 a. What
is kirkendall effect? Explain by giving an example of it. (4)
b. A
plate of iron is exposed to a carburizing (carbon-rich) atmosphere on one side
and a decarburizing (carbon-deficient) atmosphere on the other side at
. If a condition of steady state is achieved, calculate the
diffusion flux of carbon through the plate if the concentrations of carbon at
positions of 5 and 10 mm (
and 
m) beneath the carburizing surface are 1.2 and 0.8 kg/m3, respectively.
Assume a diffusion coefficient of 
at this temperature.
(6)
c. Explain
the term superconductivity. Name some of the important superconductivity
elements, compounds and alloys. (6)
Q.5 a. The
atomic weight and density of sulphur are 32 and 2.08 gm/cm3, respectively. The
electronic polarizability of the atom is
. If the sulphur solid has cubical symmetry, what will be its
relative dielectric constant? (8)
b. What
is dielectric loss? Show that dielectric loss tangent is given by:
. (8)
Q.6 a. Differentiate
hard and soft magnetic materials. Explain why Fe-Si alloys are used for power
frequencies, whereas Ni-Fe alloys are used for higher communication
frequencies. (8)
b. Define
Ferromagnetism. The elements Fe, Co, and Ni are magnetized spontaneously, whereas Cu does not, why? (8)
Q.7 a. Calculate the value of hall voltage of an n-type 3 mm wide
germanium sample having a donor density of 1021/ m3. The sample is
having a current density of 500 A/m2 and is kept in a
magnetic field of 0.5 T. (4)
b. How
are p-type and n-type semiconductor obtained? Obtain an expression for the
carrier concentration for an intrinsic semi-conductor. (8)
c. Calculate the resistivity of pure silicon at
473 K if at room temperature of 300 K the electrical resistivity of pure
silicon is 2300
.(Take energy gap = 1.1 eV, K = 
.) (4)
Q.8 a. Explain how the avalanche break down occurs
in reverse biased p-n junction diode? Derive the equation for break down
voltage. (8)
b.
Compare normal Zener diode with heavily doped Zener diode. (8)
Q.9 Practical methods for preparing junction
devices can be classified into following four main generic groups according to
way the junction is fabricated. Explain each of them. (44)
(i) Grown
junction. (ii) Alloyed junction.
(iii)
Diffused junction. (iv)
Epitaxial diffused junction Diode.