Code: D-04                                                                    Subject: ENGINEERING MATERIALS

Time: 3 Hours                                                                 June 2006                                     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 is

(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 in colour.

             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) an Oscillator.                                 (D) a Coupler.

             i.    The conductivity of an extrinsic semiconductor

(A)  decreases 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.   Name and explain the factors on which resistivity of a conducting material depends.            (4)

             b.   The field resistance of a dc machine is 50 ohm at C. The resistance increases to 55 ohm at C. Find the temperature coefficient of the resistance material.                                                          (4)

             c.   Explain the suitability of copper and aluminium that is used as electrical conducting materials.                                                                      (8)

Q.3     a.   What is super conductivity? Explain the effect of magnetic field on superconductors. Also give a few applications of superconductors.          (8)

             b.   Give one application of each of the contact materials: constantan, German silver, manganin, nichrome.                                                                    (4)

     c.   What are thermocouples? Give two examples of the most commonly used thermocouples.              (4)

Q.4     a.   Explain ionic and oriental polarisation.  (6)

b.   Explain the following terms: Dielectric constant, dielectric loss angle.                    (6)

             c.    Give the properties and applications of mica.                                                      (4)

Q.5     a.   Explain Ferroelectricity and piezoelectricity.                                                        (8)

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

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

             b.   What are ferrites? Why are they used in high frequency devices?                         (6)

             c.   Explain the hysteresis loop of a magnetic material.                                               (4)

Q.7     a.   Classify the magnetic materials into diamagnetic, paramagnetic,  ferromagnetic and ferrimagnetic materials. Also give examples of each.                 (12)

b.   Explain the factors affecting permeability and hysteresis loss.                               (4)

Q.8     a.   Explain the working of a NPN transistor.                                                            (8)

             b.   What is meant by doping? Explain the two types of materials that are formed after doping.              (8)

Q.9     a.   Draw the symbols and diagrams of both P-channel and N-channel MOSFET. Also explain the construction of a MOSFET.                                    (8)

b.   Explain a P-N junction with a suitable diagram.                                                   (8)