Code: D-04 Subject: ENGINEERING MATERIALS

Time: 3 Hours Max. Marks: 100

NOTE: There are 11 Questions in all.

Question 1 is compulsory and carries 16 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

Answer any THREE Questions each from Part I and Part II. Each of these questions carries 14 marks.

Any required data not explicitly given, may be suitably assumed and stated.

Q.1 Choose the correct or best alternative in the following: (2x8)

a. Materials, which provide a path to the magnetic flux, are classified as

(A) insulating materials. (B) semi conducting materials.

(C) magnetic materials. (D) dielectric materials.

b. Germanium possesses

(A) one valence electrons. (B) two valence electrons.

(C) three valence electrons. (D) four valence electrons.

c. Dielectric constant of vacuum is

(A) infinity. (B) 100.

(C) one. (D) zero.

d. Ferrites are

(A) ferromagnetic material. (B) ferrimagnetic materials.

(C) anti ferromagnetic material. (D) diamagnetic materials.

e. Thermocouples are used for measuring

(A) current. (B) voltage.

(C) temperature. (D) pressure.

f. The relative permeability of a paramagnetic substance is

(A) unity. (B) slightly more than unity.

(C) zero. (D) less than unity.

g. Hall effect may be used for which of the following?

(A) determining whether the semiconductor is p or n type.

(B) determining the carrier concentration.

(C) calculating the mobility.

(D) All the above.

h. Manganin is an alloy of

(A) copper, manganese and nickel. (B) copper and manganese.

(C) manganese and nickel. (D) manganese, aluminium and nickel.

PART I

Answer any THREE Questions. Each question carries 14 marks.

Q.2 a. Explain the factors which change the resistivity of a conducting material (8)

b. A heater element is made of nichrome wire having resistivity equal to ohm-m. The diameter of the wire is 0.4mm. Calculate the length of the wire required to get a resistance of 40 . (6)

Q.3 a. Explain superconductivity and explain the effect of magnetic field on superconductors. (6)

b. Give the properties and application of copper and aluminium. (8)

Q.4 a. What is polarisation? Explain. (6)

b. Give the properties and application of glass and cotton. (8)

Q.5 a. Give the names of four alloys along with their composition, which are used for making heater and thermocouple elements. (6)

b. Explain ferroelectricity and piezoelectricity. (8)

Q.6 a. Explain the electrical contact materials with examples. (7)

b. Explain the terms dielectric constant and dielectric loss angle. (7)

PART II

Answer any THREE Questions. Each question carries 14 marks.

Q.7 a. Explain the effect of temperature on the conductivity of a semiconductor. (8)

b. Explain n-type and p-type semiconductors. (6)

Q.8 Differentiate between diamagnetic, paramagnetic, ferromagnetic and ferrimagnetic materials and give examples of each. (14)

Q.9 a. Give the properties and uses of silicon iron alloy and nickel iron alloy. (6)

b. Explain the working of an npn transistor. (8)

Q.10 a. What is meant by doping? How does it affect a semiconductor? (6)

b. Explain the factors affecting permeability and hysterisis loss. (8)

Q.11 Write notes on

(i) Classification of materials on the basis of energy band. (7)

(ii) Germanium and silicon. (7)