43. An ideal conducting material has
A. zero conductivity
B. small conductivity
C. large conductivity
D. infinite conductivity
44. Superconductors are
A. monovalent metals
B. ferromagneti and antiferromagnetic metals
C. ferrimagnetic metals
D. amorphour thin films of Be, Bi and Fi.
45. Soft superconductor follow
A. Silsbee's rule alone
B. Meissner effect alone
C. both (a) and (b) above
D. none of the above
46. Hard superconductors observe
A. breakdown by Silsbee's rule
B. incomplete Meissner effect
C. high critical field and transition temperature
D. all of these
47. Superconductivity is observed for
A. dc and low frequencies
B. high frequencies
C. microwave frequencies
D. infra-red frequencies
48. Two wires A and B of the same material and lengths L and 2L have radius r and 2r respectively. The ratio of their specific resistance will be
A. 1:1
B. 1:2
C. 1:4
D. 1:8
49. The skin depth of copper is found to be 66 im at 1 MHz at a certain temperature. At the same temperature and at 2MHz, the skin depth would be approximately
A. 47 gm
B. 33 1.1M
C. 92 gm
D. 122 11111
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