211. Permanent magnets are normally made of
A. alnico alloys
B. aluminium
C. cast iron
D. wrought iron
212. Energy stored by a coil is doubled when its currest is increased by ...... percent.
A.25
B.50
C.41.4
D.100
213. The rate of rise of current through an inductive coil is maximum
A. at 63.2% of its maximum steady value
B. at the start of the current flow
C. after one time constant
D. near the final maximum value of current
214. When both the inductance and resistance of a coil are doubled the value of
A. time constant remains unchanged
B. initial rate of rise of current is doubled
C. final steady current is doubled
D. time constant is halved
215. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is .... A/s
A.50
B.20
C.0.05
D.500
216. A material for should have
A. low hysteresis loss
B. high permeability
C. low retentivity
D. high retentivity
217. Conductivity is analogous to
A. retentivity
B. resistivity
C. permeability.
D. inductance
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