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Electrical Engineering Objective Questions { Material And Components }

64. The transition temperature of mercury is
A. 0? K
B. 20? K to 40? K
C. 4.12? K
D. above 60? K

65. Superconducting material on being subject to critical field changes to
A. normal state
B. superconductivity which is independent of temperature
C. remains uninfluenced
D. critical conductivity

66.  Wire wound crypton is a super conductor having
A. copper as control wire and tungsten as gate wire
B. tungsten as control wire and tantatum as gate wire
C. tantatum as a control wire and niobium as a gate wire
D. niobium as control wire and tantatum as gat wire

67. A superconducting material when placed in a magnetic field will
A. not influence the magnetic field
B. repel all the magnetic lines of force passing through it
C. attract the magnetic field towards its centre
D. attract the magnetic field but transfer it into a concentrated zone

68. Value of critical current density Jc in a superconductor depends upon
A. temperature alone
B. magnetic field alone
C. both temperature and magnetic field
D. Silsbee effect

69. Transition temperature Tc and critical field I-1c for a superconductor are related as
A. H = Te (1 ? Ho)
B. He = Ho [I ? (--)21
C. He = H41 ? ?T
D. Te =T(1 ?

70. Superconductors are currently used for
A. reducing 12R losses
B. generating very strong magnetic field -
C. generating very strong electric field
D. generating regions free from electric or magnetic fields

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