20635511
Descripción
Test por Owen Ryan Ang, actualizado hace más de 1 año
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Creado por Owen Ryan Ang
hace más de 4 años
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Pregunta 1
Pregunta
The coefficient of self-inductance of a coil is defined as
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NI/Φ
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NΦ/I
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Φ/NI
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ΦI/N
Pregunta 2
Pregunta
Which of the following statement is incorrect?
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Whenever the flux linking with the coil or circuit changes the emf is produced.
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The direction of dynamically induced emf can be determined by Flemming's right hand rule.
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Coefficient of coupling for tightly coupled coil is zero.
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The coefficient of self-inductance is proportional to the square of number of turns on it.
Pregunta 3
Pregunta
Which of the following statements about inductance of a coil is true?
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Inductance is a characteristic of coil occurring only in case of A.C.
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Inductance appears only if the coil has an iron core.
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Inductance is only another expression for self-induced voltage.
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Inductance characterizes the magnetic properties of a coil which are significant for the value of self-induced voltage generated due to current change in the coil.
Pregunta 4
Pregunta
A collapsing field around a coil
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tends to oppose the decay of coil current
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helps the decay of coil current
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tends to aid current flow reversal
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does not affect the coil current flow
Pregunta 5
Pregunta
Energy stores in an inductance is given by
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2LI2 joules
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0 joule
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NΦ/I joules
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1/2 LI2 joules
Pregunta 6
Pregunta
Which of the following is a vector quantity?
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magnetic potential
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flux density
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magnetic field intensity
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relative permeability
Pregunta 7
Pregunta
A conductor of length L has current I passing through it, when it is placed parallel to a strong magnetic field. The force experience by the conductor will be
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BLI
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zero
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B2LI
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BL2I
Pregunta 8
Pregunta
Whenever a conductor cuts magnetic flux, an emf is induced in that conductor. This statement is due to
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Joule's law
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Coulomb's law
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Faraday's law
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Weber and Ewing's theory
Pregunta 9
Pregunta
The left hand rule correlates
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self induction, mutual induction and direction of force on a conductor
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magnetic field, electric field and direction of force on a conductor
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current, induced emf and direction of force on a conductor
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current, magnetic field and direction of force on a conductor
Pregunta 10
Pregunta
In the left hand rule, thumb always represents
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voltage
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current
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direction of force on conductor
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magnetic field
Pregunta 11
Pregunta
The coefficient of coupling between two air core coils depends upon
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self inductance of the two coils only
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mutual inductance between the two coils onjly
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mutual inductance and self inductance of the two coils
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none of the above
Pregunta 12
Pregunta
While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electric circuit?
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e.m.f.
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current density
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conductivity
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current
Pregunta 13
Pregunta
While comparing magnetic and electric circuits, the point of dissimilarity exists while considering
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flux and current flow
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permeance and conductance
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m.m.f. and e.m.f.
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reluctance and resistance
Pregunta 14
Pregunta
The effect of the inductance of a coil on a constant direct current is that
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it strengthens the current
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it does not affect the constant direct current
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it decreases the current
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it causes a higher voltage drop
Pregunta 15
Pregunta
Good smoothing factor of a coil depends on the
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terminal voltage
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property of the wire of the coil
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inductance of the coil
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cross-sectional area of the wire of the coil
Pregunta 16
Pregunta
Leakage factor is
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less than unity
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equal to unity
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more than unity
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zero
Pregunta 17
Pregunta
The law that induces emf and current always opposes the cause producing them was discovered by
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Lenz
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Faraday
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Maxwell
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Ohm
Pregunta 18
Pregunta
According to Lenz's law the direction of induced e.m.f. and hence current
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may be found by the right hand rule
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always opposes the cause producing it
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is determined by the rate of cutting flux
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may be found by the left hand rule
Pregunta 19
Pregunta
Sparking occurs when a load is switched off because the resistance has high
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capacitance
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inductance
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resistance
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impedance
Pregunta 20
Pregunta
The flux linked with a coil of inductance L carrying current i is d/dt(Li)
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True
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False
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Partly true
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Partly false
Pregunta 21
Pregunta
When steel toroidal ring is magnetized by passing current through its coil, it develops no magnetic poles
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True
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False
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Partly true
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Partly false
Pregunta 22
Pregunta
Air gap in the iron core of an inductor prevents
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hyteresis loss
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flux change
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transformer action
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core saturation
Pregunta 23
Pregunta
The growth of current in an inductive circuit follows
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hyperbolic law
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Ohm's law
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exponential law
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linear law
Pregunta 24
Pregunta
The time constant of an inductive circuit is defined as
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R/L
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Rt/L
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Lt/R
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L/R
Pregunta 25
Pregunta
The time constant is the time it takes the current of an inductive circuit to rise to
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66% of its final steady state value
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70% of its final steady state value
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63% of its final steady state value
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50% of its final steady state value
Pregunta 26
Pregunta
Mutual inductance can also be defined as
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M = N2 dΦ/dt
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M = N2 dt/di
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M = N2 di/dt
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M = N2 dt/dΦ
Pregunta 27
Pregunta
The mutual inductance of two coils is maximum when the coils are
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inclined at an angle of 45 degrees
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at right angle to each other
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facing each other
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touching each other
Pregunta 28
Pregunta
The value of mutual inductance in terms of self inductance of the two coils L1 and L2 is proportional to
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L1L2
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L1/L2
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√L1√L2
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√L1L2
Pregunta 29
Pregunta
Coupling coefficient k, a term much used in radio work can be obtained from
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K = M√L1L2
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K = M√L1/L2
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K = M/√L1L2
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K = ML1L2
Pregunta 30
Pregunta
The coupling coefficient denotes
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the degree of magnetic linkage
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whether the reluctance remains constant
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the variation of inductance between the two coils
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whether the flux linkage is constant
Pregunta 31
Pregunta
it is difficult to magnetize steel because of its
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low permeability
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high retentivity
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high permeability
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high density
Pregunta 32
Pregunta
In electrical machines, laminated cores are used with a view of reducing
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eddy current loss
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copper loss
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hysteresis loss
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windage loss
Pregunta 33
Pregunta
The area of hysteresis loop represents hysteresis loss in
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J/m3/s
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J/cycle
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J/s
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J/m3
Pregunta 34
Pregunta
According to hysteresis law, hysteresis loss in a material is proportional to
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B^1.2
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B^1.6
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B^0.6
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B^3.6
Pregunta 35
Pregunta
A degaussing is the process of
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removing gases from materials
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removal of magnetic impurities
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demagnetizing metallic part
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magnetizing nonmetallic part
Pregunta 36
Pregunta
Hysteresis losses can be reduced by
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using grain-oriented silicon steel
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increasing the frequency of the field
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laminating the core
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none of these
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