Top 350+ Solved Electromagnetics MCQ Questions Answer
Q. An air gap is usually inserted in magnetic circuits to
a. increase m.m.f.
b. increase the flux
c. prevent saturation
d. none of the above
Q. The relative permeability of a ferromagnetic material is
a. less than one
b. more than one
c. more than 10
d. more than 100 or 1000
Q. Permeability in a magnetic circuit corresponds to in an electric circuit.
a. resistance
b. resistivity
c. conductivity
d. conductance
Q. Point out the wrong statement.Magnetic leakage is undesirable in electric machines because it
a. lowers their power efficiency
b. increases their cost of manufacture
c. leads to their increased weight
d. produces fringing
Q. Permanent magnets are normally made of
a. alnico alloys
b. aluminium
c. cast iron
d. wrought iron
Q. Those magnetic materials are best suited for making armature and transformer coreswhich have permeability and hystersis loss.
a. high, high
b. low, high
c. high, low
d. low, low
Q. 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
Q. 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
Q. A material for good magnetic memory should have
a. low hysteresis loss
b. high permeability
c. low retentivity
d. high retentivity
Q. In a magnetic material hysteresis loss takes place primarily due to
a. rapid reversals of its magnetisation
b. flux density lagging behind magnetising force
c. molecular friction
d. it high retentivity
Q. Those materials are well suited for making permanent magnets whichhave retentivity and coercivity.
a. low, high
b. high, high
c. high, low
d. low, low
Q. If the area of hysteresis loop of a material is large, the hysteresis loss in this materialwill be
a. zero
b. small
c. large
d. none of the above