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. Eddy current loss is proportional to the 

(A) frequency.                                     (B) square of the frequency.

(C) cube of the frequency.                   (D) square-root of the frequency.

             b.   A pure semiconductor under ordinary conditions behaves like

(A) a conductor.                                 (B) an insulator.

(C)  a magnetic material.                      (D) a ferro-electric material.

             c.   In p-type semiconductor the majority carriers are

(A) holes.                                           (B)  electrons.

(C)  positive ions.                                (D)  negative ions.

             d.   Copper is completely miscible with

(A) nickel.                                          (B) gold.

(C)  hydrogen.                                     (D) lead.

             e.   For germanium the forbidden gap is

(A) 0.15ev.                                        (B)  0.25ev.

(C)  0.5ev.                                          (D)  0.7ev.

             f.    The dielectric strength of transformer oil should be 

(A) 100 V.                                         (B)  5 KV.

(C)  30 KV.                                        (D)  132 KV.                    

             g.   Resistivity of conductors is most affected by  

(A) composition.                                (B)  temperature.

(C)  pressure.                                      (D)  current.

             h.   Copper constantan is used for measuring temperature upto

(A)  .                                     (B)  .

(C)  .                                       (D)  .

PART I

Answer any THREE Questions. Each question carries 14 marks.

Q.2     a.   What is resistivity?  Explain the effect of temperature on the resistivity of conducting materials and define temperature coefficient of resistance.    (8)

             b.   The resistance of a wire is 60 at  and  at .  Find the resistance of wire at  and value of temperature co-efficient at .      (6)

Q.3     a.   Explain the effect of temperature on electrical conductivity of metals.                   (6)

b. Give the applications of carbon and steel.                                                           (8)

Q.4     a.   Explain the phenomenon of breakdown in dielectric materials.                             (6)

             b.   Give the properties and applications of mica and PVC.                                       (8)

Q.5     a.   Give some applications of constantan, German silver, manganin, and nichrome.                   (1½ x 4)

b.   Explain ionic and oriental polarisation.  (8)

  Q.6     a.   What are superconductors?  Give some applications of superconductors.            (6)

b.   Explain Hall effect and give some applications of Hall effect.                                (8)

PART II

Answer any THREE Questions. Each question carries 14 marks.

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

b.   Explain a p-n junction.                                                                                      (6)

Q.8     a.   Explain the terms: valence band, conduction band, valence electrons, and energy gap with the help of suitable diagrams.                                             (2 x 4)

             b.   Explain ferrites and its uses in high frequency devices.                                         (6)

Q.9     a.   Explain the hysteresis loop of a magnetic material.                                               (6)

b.   Give the classification of magnetic materials and explain each with examples.                       (8)

Q.10           a.                                                        Explain the working of a pnp transistor.   (8)

b.   Explain the construction of a MOSFET.  Draw the symbols and diagrams of both P-channel and N-channel MOSFET.                                           (6)

Q.11                                                                      Write notes on

(i) Piezoelectricity and its applications.                                                        (7)

(ii) Intrinsic and extrinsic semiconductors.                                                    (7)