Chapter 3 : Electromagnetism
141. Permeability in a magnetic circuit corresponds to ...... in an electric circuit.
A. resistance
B. resistivity
C. conductivity
D. conductance
...
Answer is ( C)
142. Point out the wrong statement. magnetic leakage is undesirable in electric machines because it
A. leads to their increased weight
B. produces fringing
C. lowers their power efficiency
D. increases their cost of manufacture
144. Permanent magnets are normally made of
A. alnico alloys
B. aluminium
C. cast iron
D. wrought iron
...
Answer is (A)
145. Energy stored by a coil is doubled when its currest is increased by ...... percent.
146. The rate of rise of current through an inductive coil is maximum
A. after one time constant
B. near the final maximum value of current
C. at 63.2% of its maximum steady value
D. at the start of the current flow
...
Answer is (D)
147. When both the inductance and resistance of a coil are doubled the value of
A. final steady current is doubled
B. time constant is halved
C. time constant remains unchanged
D. initial rate of rise of current is doubled
148. 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
... Answer is (D)149. A material for should have
A. low hysteresis lossB. high permeability
C. low retentivity
D. high retentivity
150. Conductivity is analogous to
A. permeability.
B. inductance
C. retentivity
D. resistivity
...
Answer is (A)
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