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 dielectric constant of air is practically taken as

(A)  Unity                                            (B)  More than unity

(C)   Zero                                            (D)  Less than unity

b. The covers of electrical machines are made of

(A) Soft magnetic materials                

(B)  Hard magnetic materials

(C)  Superconductors                         

(D)  Semiconductors

             c.   The material with lowest resistivity is

(A) Constantan.                                  (B)  Silver.

(C)  Manganin.                                    (D)  Nichrome.

             d.   Hysteresis loss least depends on

(A)  Frequency.                                 

(B) Magnetic field intensity.

(C)  Volume of the material.               

(D) Grain orientation of material.        

             e.   Ceramics are good

(A) Insulators                                     (B)  Conductors

(C)  Superconductors                          (D)  Semiconductors

             f.    Manganin is an alloy of

(A) Copper, manganese and nickel    

(B)  Copper & manganese

(C)  Nickel & manganese                   

(D)  Aluminium, manganese & nickel

             g.   The dielectric strength of transformer oil should be  

(A) 100 V                                          (B)  6 KV

(C)  30 KV                                         (D)  132KV          

             h.   Resistivity of conductors is most affected by

(A) Composition.                                (B) Temperature.

                   (C) Pressure.                                       (D) Current.

             i.     In silicon the forbidden gap is

(A)  1.1eV.                                         (B)  0.25 eV.

(C)  0.5 eV.                                        (D)  0.7eV.           

             j.    In order to obtain P-type germanium, it should be doped with a

(A)  Tetravalent impurity.                    

(B)  Pentavalent impurity.

(C)  Trivalent impurity.                        

(D) Any of the above will do.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Classify the conducting materials and give their properties.                                  (8)

     b.   Explain the properties and applications of 

                   (i) Asbestos                                        

                   (ii) PVC                                                                                                             (8)

Q.3     a.   Explain the magnetisation- curves of magnetic materials.                                      (8)

b.   Explain the significance of the loss tangent of a dielectric material.                        (8)                      

Q.4     a.   Write a note on superconductors.                                                                       (8)

b.   Give the four alloys & their composition, which are used for making heater and thermocouples elements.                                                                (4)

c.   Write a note on thermocouples.                                                                          (4)

Q.5     a.   Explain the P-N junction with a suitable diagram.                                                (8)

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

  Q.6     a. Explain the effect of temperature on electrical conductivity of metals.                   (8)

             b.   Give the properties & applications of carbon & steel.                                          (8)

Q.7     a.   Explain ferroelectricity and piezoelectricity& also give their applications.              (8)

             b.   Write the properties & applications of silicon & nickel iron alloy.                         (8)

Q.8     a.    Explain the terms Valence Electrons, Conduction Band, Valence Band & Energy Gap with   suitable diagrams.                                            (8)

             b.   Explain ferrites and give their applications.                                                          (8)

Q.9     a.   Explain Hysteresis loop of magnetic materials.                                                     (8)

b.   With examples explain diamagnetic, paramagnetic  & ferromagnetic materials.                     (8)