Electromagnetics Field (3140912) MCQs

MCQs of Magnetic forces, materials and inductance

Showing 91 to 100 out of 171 Questions
7 8 9 10 11 12
91.
Magnetic leakage is undesirable in electric machines because it
(a) Increases weight
(b) Increases cost of manufacturing
(c) Produces fringing
(d) All of above
Answer:

Option (d)

92.
Relative permeability of vacuum is
(a) 1
(b) 1 H/m
(c) 4π × 10–7 H/m
(d) 4π H/m
Answer:

Option (a)

93.
Permanent magnets are normally made of
(a) Alnico alloys
(b) Aluminium
(c) Cast iron
(d) Wrought iron
Answer:

Option (a)

94.
Energy stored by a coil is doubled when its current is increased by percent?
(a) 25
(b) 50
(c) 41.4
(d) 100
Answer:

Option (c)

95.
Those magnetic materials are best suited for making armature and transformer cores which have____permeability and_______hysteresis loss.
(a) High, high
(b) Low, high
(c) High, low
(d) Low, low
Answer:

Option (c)

96.
The rate of rise of current through an inductive coil is maximum at
(a) 63.2% of its maximum steady value
(b) The start of the current flow
(c) One time constant
(d) Final maximum value of current
Answer:

Option (b)

97.
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
Answer:

Option (a)

98.
A material for good magnetic memory should have
(a) Low hysteresis loss
(b) High permeability
(c) Low retentivity
(d) High retentivity
Answer:

Option (d)

99.
Conductivity is analogous to
(a) Retentivity
(b) Resistivity
(c) Permeability
(d) Inductance
Answer:

Option (c)

100.
In a magnetic material hysteresis loss takes place primarily due to
(a) Rapid reversals of its magnetization
(b) Flux density lagging behind magnetizing force
(c) Molecular friction
(d) High retentivity
Answer:

Option (d)

Showing 91 to 100 out of 171 Questions
7 8 9 10 11 12