Electrical material objective Question

1➤ In the magnetic core the electromotive forces (emf) induced in accor- dance with Faraday's law of electromagnetic induction give rise to

field current.armature current.excitation currenteddy current

2➤ The important considerations to be made in selection of materials is /are

Ease of fabrication Availability CostAll of these

3➤ The converse of magnetostriction effect is

Villari effectSkin effectSee back effectSkin effect

4➤ Which of the following inductors will have the least eddy current losses?

Wooden coredAir cored Iron coredLaminated iron cored

5➤ When a ferromagnetic substance is magnetized the phenomenon of 'magnetostrictriction' causes

Small changes in its dimensions Change in permeability of the substance Decrease in saturation flux-densityIncrease in the body temperature

6➤ Conductivity of aluminium is _______time of copper

2.50.60.41.63

7➤ Which one of the following materials has temperature coefficient of resistance very close to zero

NichromeCarbon MaganinAluminium

8➤ Platinum is employed in

Electrical contacts and thermocouple Grids for special purpose vaccum tubesAll of theseHeating elements for electric furnace

9➤ High frequency transformer cores are generally made from

Mu-metalCobaltNone metalFerrites

10➤ Wire wound resistances are used only when

High power rating is necessary Precision is essential Low values are required Costly equipment are manufactured

11➤ Maximum flux density in cold rolled grain Oriented steel is

2.01.51.10.5

12➤ The shape B-H curve for air gap is

ParabolaEllipseStraight line Sinusoidal

13➤ Total number of electrons that can be accommodated in various electron states in a valance band of given solid is equal to

Atomic number of solidThe number of atoms in the solidHalf of number of atoms in solidAll of these

14➤ The coordination number of a cubic structure is

8624

15➤ The difference between the number of atoms in a unit cell of a BCC crystal and FCC crystal is

1462

16➤ What type of defects causes F-centers in a crystal

Stoichiometric defectMetal excess defects due to anion vacancies Frenkel effectMetal excess defect due to extra cations

17➤ In ionic crystal electrical conductivity is

Practically zeroDepends on temperature Very highDepends on material

18➤ In. Crystal lattice what are the vacancies created by the absence of certain things atoms known as

Hertz defectPauli defectsSchottky defectsCrystal defects

19➤ Epitaxial III-V group semiconductor compounds have which one of the following crystal structure?

BCCZinc blendsFCCHexagonal

20➤ Specific resistance of a conductor depends upon

Dimensions of the conductor Composition of conductor material Both a and bResistance of conductor

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