DipIETE
– ET (OLD SCHEME)
Code: DE04 Subject:
ENGINEERING MATERIALS
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. Which
material has the highest electrical conductivity?
(A)
Steel (B) Silver
(C) Aluminium (D) Lead
b. Which of the following materials has negative resistance temperature coefficient?
(A)
Tungsten (B) Steel
(C) Tin (D) Carbon
c. The temperature beyond which
substances lose their ferroelectric properties, is known as_________.
(A) Critical temperature (B) Curie temperature
(C) Inversion temperature (D) Conversion
temperature
d. Which of the following is piezo-electric material?
(A)
Quartz (B)
Silica Sand
(C) Corrundum (D)
Polystyrene
e. Which of the following materials is particularly suitable for use in standard resistance coils and in instrument shunts?
(A) Nichrome (B) Graphite
(C) Magnesium (D) Alnico
f. Which of the following is not a permanent magnetic material?
(A)
Chromium
steel (B)
Silicon iron
(C) Cobalt steel (D) Alnico
g. A good electric contact material have all of the following properties EXCEPT ____________.
(A) high melting point (B) good thermal conductivity
(C) high resistivity (D)
high resistance to erosion
h. Electrical resistance of a semi-conductor ____________.
(A) increase with temperature
(B) decrease with temperature
(C) remains constant with temperature
(D) None of the above
i. The Fermi level is _________________.
(A) an
average value of all available energy levels
(B) the
highest occupied energy levels at 
K
(C) an
energy level at the top of valence band
(D) the
largest available energy levels
j. In a PNP transistor, with normal bias, the emitter junction _____________.
(A) is always reverse biased (B) offers very high resistance
(C) offers a low resistance (D) remains open
Answer
any FIVE Questions out of EIGHT Questions.
Each
question carries 16 marks.
Q.2 a. Explain the electron gas model of a
metal. (8)
b. Explain
the term super conductivity. Mention their applications in electrical and
electronics engineering. (8)
Q.3 a. Mention two applications of each of the
following conducting materials:
(i) Copper (ii) Aluminium
(iii) Tungsten (iv) Iron & Steel
(v) Alloys (vi) Nickel
(vii) Carbon and Graphite (viii) Lead (8)
b. Explain the effect of temperature on
electrical conductivity of metals. (8)
Q.4 a. Explain the phenomenon of polarization. What
are the different types of polarization? (8)
b. Explain the following:
(i) Dielectric constant
(ii) Dielectric
Loss
(iii) Significance
of the loss tangent (2+2+4)
Q.5 a. Explain
the phenomenon of ‘Piezo electricity’ and give some examples & uses of
Piezo Electric material. (8)
b. What are the important requirements of good insulating materials?
Give two examples and their uses. (8)
Q.6 a. Give classification of magnetic materials. (8)
b. What are ferrites? Explain their suitability
for high frequency applications. (8)
Q.7 a. What specific material would you suggest for
the following application? Give reason
in each case.
(i) for making permanent magnet
(ii) for
electrical machine and transformer cores (4+4)
b. Distinguish
between conductors, semiconductor and insulators with the help of energy band
diagrams. (8)
Q.8 a. What are the different types of
semiconductors? Describe in brief with examples. (8)
b. What is a junction transistor? Describe in
brief working of two types of
transistor. (8)
Q.9 Write
short notes on:
(i) Einstein Relation.
(ii) Diffusion. (8+8)