DipIETE – ET (OLD SCHEME)

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 the best alternative in the following:                                 (2 10)

a. ACSR (Aluminium Conductor Steel Reinforced) are used as

(A)  overhead transmission lines.          (B)  super conductors.

(C)   fuse.                                            (D)  underground cables.

b. The dielectric constant of air is taken as

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

(C)  less than unity.                              (D)  zero.

             c.   Thermocouples are used for the measurement of

(A) humidity.                                      (B)  current.

(C)  voltage.                                        (D)  temperature.

             d.   Permanent magnets are made of

(A)  soft magnetic materials.                (B) hard magnetic materials.

(C)  semi conductors.                          (D) super conductors.       

             e.   All semiconductors in their last orbit have

(A) 8 electrons.                                  (B)  2 electrons.

(C)  4 electrons.                                  (D)  6 electrons.

             f.    The critical temperature above which, the ferromagnetic materials loose their magnetic property is known as

(A) hysteresis.                                    (B)  curie point.

(C)  transition temperature.                  (D)  standard temperature.

             g.   n-type semiconductor is an example of   

(A) extrinsic semiconductor.               (B)  intrinsic semiconductor.

(C)  superconductor.                           (D)  insulators.      

             h.   Materials which provide a path to the magnetic flux, are called

(A) insulating materials.                       (B)  semiconducting materials.

                   (C) magnetic materials.                        (D) dielectric materials.

             i.    Ferrites are

(A)  ferromagnetic materials.                (B)  ferrimagnetic materials.

(C)  anti ferromagnetic materials.          (D)  diamagnetic materials.

             j.    For which of the following Hall effect may be used?

(A)  Calculating the mobility.               

(B)  Determining the type of semiconductor.

(C)  Determining the carrier concentration.

(D)  All the above.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Define resistivity of a material.  Explain the factor affecting the resistivity of conducting materials.                                                                (2+6)

     b.   Explain the effect of magnetic field on superconductors.  Give a few applications of superconductors.                                                                     (5+3)

Q.3     a.   Give a few applications of constantan, German silver, manganin, nichrome.                         (4 2)

b.   Explain ferroelectricity and piezoelectricity.  Give a few examples of each.

(2 4)                      

Q.4     a.   Explain hysteresis loop of magnetic materials.                                                      (6)

b.   An electric heater element is made of nichrome wire having resistivity equal to ohm-metre.  The diameter of the wire is 0.3 mm.  Calculate the length of the wire required to get a resistance of 30 ohms.                                                           (5)

c. Explain the electrical contact materials with examples.                                         (5)

Q.5     a.   Explain the effect of a dielectric on the behaviour of a capacitor.                          (8)

     b.   Explain the properties and applications of

                   (i)   cotton                                           (ii)   porcelain                                          (8)

  Q.6     a. Explain the phenomenon of breakdown in dielectric material.                               (8)

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

Q.7     a.   Give the applications and properties of Iron, Silicon Iron alloy and Nickel Iron alloy.                       (7)

             b.   Explain ferromagnetic domains, magnetization curve and hysteresis loop.             (9)

Q.8     a.    Classify the materials into conductors, semiconductors and insulators.                 (8)

             b.   Explain the working of a p-n-p transistor and their characteristics.                       (8)

Q.9     a.   Explain the effect of temperature on the conductivity of the semiconductor.          (6)

b.   Write short note on:-

(i)   Types of semiconductors.                                                                            (5)

(ii)  Hall effect.                                                                                                   (5)