Electrical Engineering Materials Question Paper of 3rd Semester Electrical(D) Download Previous Years Question Paper 5

S.B. Roll No.______

ELECTRICAL ENGINEERING MATERIALS

3^rd Exam/Elect/5243/May’06

Duration: 3 hrs.

Note: Attempt any five questions.

1.      

a.     Give the atomic structure of any one of the semi conductor materials and explain how it differs form that of conducting and insulating materials.

b.     A length of wire has a resistance of 14.5 ohms. Find the resistance of another wire of the same material, three times as long and twice a big in cross sectional area.

2.      

a.     Explain why copper is used in the windings of electrical machines and in flexible wires oven through it is expensive.

b.     Write down the names of the alloys composed of the following metals:

                                                             i.      Iron –chromium-nickel

                                                           ii.      Nickel-copper

                                                        iii.      Copper-nickel

                                                        iv.      Copper manganese-nickel

                                                           v.      Copper zinc

c.      State one application of each of the following in electrical field

                                                             i.      Tungsten

                                                           ii.      Carbon

                                                        iii.      Mercury

                                                        iv.      Silver

                                                           v.      Platinum

3.       

a.     State the properties of semi conducting materials.

b.     How is insulation resistance affected by?

                                                             i.      Temperature

                                                           ii.      Age

                                                        iii.      Moisture

                                                        iv.      Applied voltage

c.      In case of insulating materials, define the following:

                                                             i.      Volume resistivity

                                                           ii.      Solubility

                                                        iii.      Weather ability

4.       

a.     Mention one electrical application of each of the following insulating material.

                                                             i.      Rubber

                                                           ii.      Impregnated paper

                                                        iii.      Class wool

                                                        iv.      Asbestos

                                                           v.      Bakelite

b.     State the purpose of Enameling, mention a few enamels with their applications

c.      Which of the following are thermosetting or thermoplastic materials.

                                                             i.      PVC

                                                           ii.      Polyethylene

                                                        iii.      Epoxy resins

                                                        iv.      Bakelite

5.       

a.     State the difference between soft magnetic material and hard magnetic material.

b.     How do the above two magnetic materials differ form each other?

c.      State the properties of these two magnetic materials and applications.

6.       

a.     Explain briefly the reasons for the following

                                                             i.      Hearing element is not made of iron

                                                           ii.      Conducting materials should have a low valve of temperature co-efficient of resistance

                                                        iii.      Air is replaced by nitrogen as an insulating material in certain applications

                                                        iv.      The windings of power transformer are immersed in oil.

                                                           v.      Synthetic rubber is inferior to natural rubber in electrical properties.

b.     Explain the phenomenon of hysteresis

7.       

a.     What are bimetals ? where are they used?

b.     State the advantages of cartridge fuse over Rewritable fuse.

c.      State the applications of nitrogen , hydrogen of SF as insulating agent.

8.       

a.     Why are conductors stranded?

b.     Name the materials used in the manufacturing of transformer core. Give reasons for you answer.

c.      What will be the effect on the rating of an apparatus if its insulation is by another of higher temperature class?