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 best alternative in the following:                                         (2x10)

a. The percentage of carbon in mild steel

(A)  0.08 to 0.3 %                               (B)  0.5 to 1.4 %

(C)   2.35 %                                        (D)  0.5 %

b. Aluminium is 

(A) Silvery white in colour                   (B)  Yellow in colour

(C)  Reddish in colour                          (D)  Pale yellow

             c.   Hard ferrites are used for making

(A) Transformer cores.                       (B)  Electrical machinery.

(C)  High frequency equipment.            (D)  Light weight permanent magnets.

             d.   The relative permeability of a paramagnetic substance is

(A)  Unity.                                          (B) Slightly more than unity.

(C)  Zero.                                           (D) Less than unity.           

             e.   The main constituents of glass is

(A) SiO₂ (B)  B₂O₃

(C)  Al₂O₃ (D)  Cr₂O₃

             f.    Micanite is a form of

(A) Built up mica                               

(B)  Hydrated potassium aluminium silicate

(C)  Magnesium mica                          

(D)  Calcium mica

             g.   What is the type of bonding in silicon?  

(A) Ionic                                            (B)  Covalent

(C)  Metallic                                        (D)  Ionic + Metallic          

             h.   P-N junction is

(A) A rectifier.                                    (B) An amplifier.

                   (C) Oscillator.                                     (D) Coupler.

             i.     The conductivity of an extrinsic semiconductor

(A)  Decrease with temperature.         

(B)  Increases with temperature.

(C)  Remains constant with temperature.   

(D)  Decreases and then increases with temperature.         

             j.    When a semiconductor is doped with a P-type impurity, each impurity atom will

(A)  Acquire negative charge.               (B)  Acquire positive charge.

(C)  Remain electrically neutral.            (D) Give away one electron.

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 ionic and oriental polarisation.  (8)

Q.3     a.   Explain the effect of a dielectric on the behaviour of a capacitor.                          (8)

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

Q.4     a.   Explain the factors affecting permeability & hysteresis loss.                                  (8)

b.   Give the properties & applications of soft iron ferrites & permanent magnet materials.                     (8)

Q.5     a.   Explain the energy band diagrams of conductors, semiconductors  & insulators.                  (8)

     b.   What meant by doping? How does it affect a semiconductor?                             (8)

  Q.6     a. Explain the terms dielectric losses and dielectric constant.                                    (8)

             b.   Explain the effect of magnetic field on superconductors. Give a few of its applications.                     (8)

Q.7     a.   Give the properties & applications of copper & aluminium.                                 (8)

             b.   An electric heater element is made of Nichrome wire having resistivity equal to 100 X 10^-8 W –m .The diameter of the wire is 0.3 mm. Calculate the length of the wire required to get a resistance of 30W.                                                           (8)

Q.8     a.    Explain the structure of Germanium & Silicon.                                                    (8)

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

Q.9           Write notes on: -                                 

(i) MOSFET.                                                                                 (8)

(ii) Hall effect.                                                                                 (8)