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Electrical Engineering
Magnetism And Electromagnetism
Quiz 3
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Q.1
Hysteresis loop in case of magnetically hard materials is more in shape as compared to magnetically soft materials.
circular
triangular
rectangular
none of the above
Q.2
The unit of flux is the same as that of
reluctance
resistance
permeance
pole strength
Q.3
A keeper is used to
change the direction of magnetic lines
amplify flux
restore lost flux
provide a closed path for flux
Q.4
Which of the following is not a unit of flux?
Maxwell
Telsa
Weber
All of the above
Q.5
When an iron piece is placed in a magnetic field
the magnetic lines of force will bend away from their usual paths in order to go away from the piece
the magnetic lines of force will bend away from their usual paths in order to pass through the piece
the magnetic field will not be affected
the iron piece will break
Q.6
Temporary magnets are used in
loud-speakers
generators
motors
all of the above
Q.7
Paramagnetic materials have relative permeability
slightly less than unity
equal to unity
slightly more than unity
equal to that ferromagnetic mate rials
Q.8
In a simple magnetic field the strength of magnet flux
is constant and has same value in energy part of the magnetic field
increases continuously from initial value to final value
decreases continuously from initial value to final value
first increases and then decreases till it becomes zero
Q.9
A conductor of length L has current I passing through it, when it is placed parallel to a magnetic field. The force experienced by the conductor will be
zero
BLI
B2LI
BLI2
Q.10
Which of the following type of materials are not very important for engineering applications?
Ferromagnetic
Paramagnetic
Diamagnetic
None of the above
Q.11
The relative permeability of materials is not constant.
diamagnetic
paramagnetic
ferromagnetic
insulating
Q.12
A permeable substance is one
which is a good conductor
which is a bad conductor
which is a strong magnet
through which the magnetic lines of force can pass very easily
Q.13
The stray line of magnetic flux is defined as
a line vertical to the flux lines
the mean length of a ring shaped coil
a line of magnetic flux in a non-uniform field
a line of magnetic flux which does not follow the designed path
Q.14
A permanent magnet
attracts some substances and repels others
attracts all paramagnetic substances and repels others
attracts only ferromagnetic substances
attracts ferromagnetic substances and repels all others
Q.15
Two infinitely long parallel conductors in vacuum any separated 1 metre between centers >then a current of 1 ampere flows the. uk each conductor, produce on each other a force of
2 x 1(T2 N/m)
2 x KT3 N/m
2 x 10"5 N/m
2x 1(T7 N/m)
Q.16
The magnetism left in the iron after exciting field has been removed is known as
permeance
residual magnetism
susceptance
reluctance
Q.17
The materials having low retentivity are suitable for making
weak magnets
temporary magnets
permanent magnets
none of the above
Q.18
One maxwell is equal to
10
-8
webers
10
-4
webers
10
8
webers
10
4
webers
Q.19
For which of the following materials the net magnetic moment should be zero?
Diamagnetic materials
Ferrimagnetic materials
Antiferromagnetic materials
Antiferrimagnetic materials
Q.20
Which of the following is a vector quantity?
Relative permeability
Magnetic field intensity
Flux density
Magnetic potential
Q.21
A coil of wire is placed in a changing magnetic field. If the number of turns in the coil is decreased, the voltage induced across the coil will
Increase
Decrease
Remain constant
Be excessive
Q.22
The retentivity (a property) of material is useful for the construction of
permanent magnets
transformers
non-magnetic substances
electromagnets
Q.23
If the steel disk in a crankshaft position sensor has stopped with the tab in the magnet's air gap, the induced voltage
Increases
Decreases
Is zero
Will remain constant
Q.24
What is the magneto-motive force (mmf) of a wire with 8 turns carrying three amperes of current?
2,400 At
240 At
24 At
2.4 At
Q.25
Magnetism of a magnet can be destroyed by
heating
hammering
by inductive action of another magnet
by all above methods
Q.26
Strength of an electromagnet can be increased by
increasing the cross-sectional area
increasing the number of turns
increasing current supply
all above methods
Q.27
When two ends of a circular uniform wire are joined to the terminals of a battery, the field at the center of the circle
will be zero
will be infinite
will depend on the amount of e.m.f. applied
will depend on the radius of the circle
Q.28
Two long parallel conductors carry 100 A. If the conductors are separated by 20 mm, the force per meter of length of each conductor will be
100 N
10 N
1 N
0.1 N
Q.29
What is the magneto-motive force in a 75-turn coil of wire when there are 4 A of current through it?
18.75 At
30 At
300 At
187 At
Q.30
The magnetic reluctance of a material
decreases with increasing cross sectional area of material
increases with increasing cross-sec-tional area of material
does not vary with increasing cross-sectional area of material
any of the above
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