Code: DE-04                                                                  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. Materials that store electrical energy are classified as  

(A)  Magnetic material                         (B)  Dielectric material

(C)   Insulating material                        (D)  Conducting material

b. Paper is hygroscopic and absorbent.

(A) True                                             (B)  False

             c.   Insulators have

(A) A full valence band.                      (B)  An empty conduction band.

(C)  A large energy gap.                      (D)  All the above.

             d.   Hysteresis loss least depends on

(A)  Frequency.                                  (B) Magnetic field intensity.

(C)  Volume of the material.                (D) Grain orientation of material.    

             e.   For Germanium the forbidden gap is

(A) 1.1ev                                           (B)  0.25ev

(C)  0.5ev                                           (D)  0.7ev

             f.    Atoms with four valence electrons are good conductos.

(A) True                                             (B)  False

             g.   Semi-conductors have ________ temperature coefficient of resistance.   

(A) Negative                                      (B)  Positive

(C)  Both positive and negative            (D)  None of the above     

             h.   Tick off the material, which is different from the group  

(A) Constantan.                                  (B) Manganin.

                   (C) Nichrome.                                     (D) Brass.

             i.     Ferrites are

(A)  Ferromagnetic materials.               (B)  Ferrimagnetic materials.

(C)  Anti ferromagnetic materials.         (D)  Diamagnetic materials.

             j.    Tick of the property, which is different from the group   

(A)  Ductility.                                       (B)  Resistivity.

(C)  Tensile strength.                            (D) Hardness.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Give three important, electrical properties of copper as a conducting material.  Why copper is preferred over aluminium for transformer windings or generator windings?                                                 (4+5)

     b.   What is superconductivity?  Give a few applications of superconductors.         (3+4)

Q.3           Explain the properties and applications of

(i)   cotton                                           (ii)   glass

                   (iii) asbestos                                        (iv)  PVC.                                        (4  4)

Q.4     a.   Differentiate between, ferroelectric and piezoelectric materials.  Give a few properties and applications of each.                                                                                                         (4+4+4)

b.   Give few applications of German silver and nichrome.                                     (2+2)

Q.5     a.   Explain Hall effect (Hall voltage, Hall Coefficient, Hall mobility and Hall angle) and its applications.                                                             (10)

     b.   A 6 V / 2.5 mA relay is connected in the output stage of a transistor.  The coil is made of aluminium having .  The resistance of the coil is 600  at .  Calculate the resistance of the coil at .                                                            (6)

  Q.6           Define polarization of a dielectric material.  Explain the different types of polarization and the effect of frequency of applied electric field on

them.                                                                                                         (2+8+6)

Q.7     a.   Give the applications and properties of silicon iron alloy and nickel iron alloy.                      (8)

             b.   Distinguish briefly between diamagnetic, paramagnetic and ferromagnetic materials.             (8)

Q.8     a.    Explain the energy bands in solids.  Also classify the materials based on the energy bands and explain them.                                                                                                                         (8)

             b.   Explain the different types of semiconductors and the conduction process in them.               (8)

Q.9     a.   Explain the effect of impurities on the conductivity of the semiconductor.              (8)

b.   Write notes on

(i) Electrical contact materials.                                                        (4)

(ii) Thermocouple.                                                                           (4)