211. Permanent magnets are normally made of
A. alnico alloys
B. aluminium
C. cast iron
D. wrought iron

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212. Energy stored by a coil is doubled when its currest is increased by ...... percent.
A.25
B.50
C.41.4
D.100

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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

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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

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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

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216. A material for should have
A. low hysteresis loss
B. high permeability
C. low retentivity
D. high retentivity

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217. Conductivity is analogous to
A. retentivity
B. resistivity
C. permeability.
D. inductance

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