Electrical Engineering Materials MCQ

21. The first critical condition at which free electrons are diffracted in an FCC crystal would occur at which one of the following values of the wave number ‘k’?(‘a’ is lattice parameter)

(a) 2/a
(b) πa/√3
(c) π/a
(d) √3π/a

22. What is the packing fraction of a BCC (body-centered cubic) unit cell ?

(a) √3π/16
(b) √3π/18
(c) √3π/12
(d) √2π/8

23. Vacant lattice sites in halide crystals cause

(a) plastic deformation and ionic conductivity.
(b) transparency and diffusion.
(c) diffusion and ionic conductivity.
(d) plastic deformation and transparency.

24. The geometrical configuration of one molecule of C_60- buckminsterfullerene contains

(a) 12 hexagons and 20 pentagons of Carbon atoms.
(b) 20 hexagons and 12 pentagons of Carbon atoms.
(c) 20 hexagons and 20 pentagons of Carbon atoms.
(d) 12 hexagons and 12 pentagons of Carbon atoms.

25. In a Hexagonal Close Packed (HCP) crystal structure, if ‘a’ and ‘c’ represent, respectively the short and long unit cell dimensions,

then (c/a) should be
(a) 12.00
(b) 0.74
(c) 1.633
(d) 16.33

26. Consider the following types of semiconductors:

1. N-type.
2. P-type.
3. Intrinsic.
4. Extrinsic.

Which of these types of semiconductors are formed by doping germanium with gallium?
(a) 1 and 3.
(b) 2 and 4.
(c) 1 and 4.
(d) 2 and 3. [I.E.S. E.E.-1, 2000]

28. The conductivity of material ‘A’ is half that of material ‘B’. The ratio of relaxation time of ‘A’ to that of ‘B’ is

(a) 0.5
(b) 1
(c) 2
(d) 4.1

29. For which one of the following materials is the Hall coefficient zero?

(a) Metal.
(b) Insulator.
(c) Intrinsic semiconductor.
(d) Alloy

31. Principle of Hall effect is used in the construction of which one of the following?

(a) Ammeter.
(b) Voltmeter.
(c) Galvanometer.
(d) Gaussmeter.

32. Consider the following statements: In a Hall effect experiment, the sign of Hall voltage will change if

1. direction of applied field is changed.
2. direction of applied magnetic field is changed.
3. direction of both applied electric and magnetic fields are changed.
4. direction of current is changed.

Which of the above statements is/are correct?
(a) 1, 2 and 3.
(b) 3 only.
(c) 1, 2 and 4.
(d) 3 and 4.

33. The band-gap of a semiconductor is 1.43 eV. Its cut-off wavelength is

(a) 1 µm
(b) 0.81 µm
(c) 0.56 µm
(d) 0.27 µm

34. When temperature of a conductor is approaching zero Kelvin, the mean free path of the free electrons in the conductor is proportional to

(a) T
(b) T³
(c) (1/T)^1/3
(d) 1/T³

35. Consider the following functions:

1. To mask against diffusion or ion implant.
2. To act as a component in MOS devices.
3. To provide low resistivity paths.
4. To facilitate the entry of dopants.

The function of an oxide layer on a silicon wafer would include
(a) 1 and 2.
(b) 2 and 3.
(c) 3 and 4.
(d) 1 and 4.

36. Consider the following statements:

1. momentum changes.
2. direction of motion changes.
3. potential energy changes.
4. kinetic energy remains constant.

Which of these statements are correct?
(a) 3 and 4.
(b) 2 and 3.
(c) 1 and 2.
(d) 1 and 4.

37. In a linear chain of atoms of inter atomic distance ‘l‘; the first Brillouin zone occurs between wave numbers

(a) -π/l and +π/l
(b) -2π/l and +2π/l
(c) zero and 2π/l
(d) -1/l and +1/l

38. The properties to be considered in selection of electrical engineering materials are

(a) physical.
(b) chemical.
(c) electrical.
(d) mechanical.
(e) thermal
(f) all of these.

39. The important consideration(s) to be made in selection of materials is/are

(a) ease of fabrication.
(b) cost.
(c) availability.
(d) all of these.

40. The electrical conductivity of metals is typically of the order of (in ohm^-1m^-1)

(a) 10⁷
(b) 10^-4
(c) 10⁵
(d) 10^-6