Hiried Electrical Engineering Materials Multiple choice Questions and Answers pdf

51. A carbon resistor contains
(a)     carbon crystals
(b)     solid carbon granules
(c)    pulverized coal
(d)    finely divided carbon black.
Ans: d

52.    Which of the following materials does not have covalent bonds ?
(a)    Organic polymers
(b)    Silicon 
(c)     Metals
Ans: c

53.    In graphite, bonding is
(a)     covalent 
(b)     metallic
(c)    Vander Waals
(d)    Vander Waals and covalent
Ans: d

54.    Total number of crystal systems is
(a)     2 
(b)     4
(c)     7 
(d)     12
Ans: c

55.    The number of atoms per unit cell in B.C.C. structure is
(a)     1 
(b)     2
(c)     4 
(d)     8
Ans: b

56.    The conductivity of a metal is determined by
(a)     the electronic concentration and the mobility of the free electrons
(6)     the number of valence electrons per atom
(c)    either (a) or (b)
(d)    none of the above
Ans: a

57.    The resistivity of a metal is a function of temperature because
(a)     the amplitude of vibration of the atoms varies with temperature
(b)     the electron density varies with temperature
(c)     the electron gas density varies with temperature
Ans: a

58.    In a crystal, an atom vibrates at a frequency determined by
(a)    the heat content of the crystal
(b)    the temperature of the crystal
(c)    the stiffness of the bonds it makes with neighbours
Ans: c

59.    Due to which of the following reasons aluminium does not corrode in atmost phere ?
(a)     Aluminium is a noble metal
(b)     Atmospheric oxygen can only diffuse very slowly through the oxide layer which is formed on the surface of aluminium
(c)     No reaction with oxygen occurs ft Any of the above
 Ans: b

60.    The impurity atoms is semiconductors
(a)     inject more charge carriers
(6)     reduce the energy gap
(c)    increase the kinetic energy of valence electrons
(d)    all of the above
Ans: b

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