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This set of Electromagnetics Multiple Choice Questions & Answers (MCQs) focuses on Electromagnetics Set 16
Q1 | The susceptibility of paramagnetic materials generally lies between
- kt3 and 1ct6
- 1ct3 and 1ct7
- kt4 and kt8
- 10"2 and kt5
Q2 | For which of the following materials the net magnetic moment should be zero ?
- diamagnetic materials
- ferrimagnetic materials
- antiferromagnetic materials
- antiferrimagnetic materials
Q3 | The attraction capacity of electromagnet will increase if the
- core length increases i
- core area increases
- flux density decreases
- flux density increases
Q4 | Which of the following statements is correct ?
- the conductivity of ferrites is better than ferromagnetic materials
- the conductivity of ferromagnetic materials is better than ferrites
- the conductivity of ferrites is very high
- the conductivity of ferrites is same as that of ferromagnetic materials
Q5 | Temporary magnets are used in
- loud-speakers
- generators
- motors
- all of the above
Q6 | Main causes of noisy solenoid are
- strong tendency of fan out of lami-nations at the end caused by repul¬sion among magnetic lines of force
- uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts
- both of above
- none of the above
Q7 | Magnetism of a magnet can be destroyed by
- heating
- hammering
- by inductive action of another magnet
- by all above methods
Q8 | An air gap is usually inserted in magnetic circuits to
- increase m.m.f.
- increase the flux
- prevent saturation
- none of the above
Q9 | The relative permeability of a ferromagnetic material is
- less than one
- more than one
- more than 10
- more than 100 or 1000
Q10 | The unit of magnetic flux is
- henry
- weber
- ampereturn/weber
- ampere/metre
Q11 | Permeability in a magnetic circuit corresponds to in an electric circuit.
- resistance
- resistivity
- conductivity
- conductance
Q12 | Point out the wrong statement.Magnetic leakage is undesirable in electric machines because it
- lowers their power efficiency
- increases their cost of manufacture
- leads to their increased weight
- produces fringing
Q13 | Relative permeability of vacuum is
- 1
- 1 h/m
- 1/4ji
- 4n x 10-\ h/m
Q14 | Permanent magnets are normally made of
- alnico alloys
- aluminium
- cast iron
- wrought iron
Q15 | Those magnetic materials are best suited for making armature and transformer coreswhich have permeability and hystersis loss.
- high, high
- low, high
- high, low
- low, low
Q16 | The rate of rise of current through an inductive coil is maximum
- at 63.2% of its maximum steady value
- at the start of the current flow
- after one time constant
- near the final maximum value of current
Q17 | When both the inductance and resistance of a coil are doubled the value of
- time constant remains unchanged
- initial rate of rise of current is doubled
- final steady current is doubled
- time constant is halved
Q18 | A material for good magnetic memory should have
- low hysteresis loss
- high permeability
- low retentivity
- high retentivity
Q19 | Conductivity is analogous to
- retentivity
- resistivity
- permeability
- inductance
Q20 | In a magnetic material hysteresis loss takes place primarily due to
- rapid reversals of its magnetisation
- flux density lagging behind magnetising force
- molecular friction
- it high retentivity
Q21 | Those materials are well suited for making permanent magnets whichhave retentivity and coercivity.
- low, high
- high, high
- high, low
- low, low
Q22 | If the area of hysteresis loop of a material is large, the hysteresis loss in this materialwill be
- zero
- small
- large
- none of the above
Q23 | Hard steel is suitable for making permanent magnets because
- it has good residual magnetism
- its hysteresis loop has large area
- its mechanical strength is high
- its mechanical strength is low
Q24 | Silicon steel is used in electrical machines because it has
- low co-ercivity
- low retentivity
- low hysteresis loss
- high co-ercivity
Q25 | Conductance is analogous to
- permeance
- reluctance
- flux
- inductance