Pregunta 1
Pregunta
The coefficient of self-inductance of a coil is defined as
Pregunta 2
Pregunta
Which of the following statement is incorrect?
Respuesta
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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
Respuesta
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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
Respuesta
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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?
Respuesta
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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
Pregunta 8
Pregunta
Whenever a conductor cuts magnetic flux, an emf is induced in that conductor. This statement is due to
Respuesta
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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
Respuesta
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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
Pregunta 11
Pregunta
The coefficient of coupling between two air core coils depends upon
Respuesta
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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?
Respuesta
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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
Pregunta 14
Pregunta
The effect of the inductance of a coil on a constant direct current is that
Respuesta
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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
Pregunta 16
Pregunta
Leakage factor is
Respuesta
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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
Pregunta 18
Pregunta
According to Lenz's law the direction of induced e.m.f. and hence current
Respuesta
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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
Respuesta
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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
Respuesta
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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
Respuesta
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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
Pregunta 25
Pregunta
The time constant is the time it takes the current of an inductive circuit to rise to
Respuesta
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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
Pregunta 28
Pregunta
The value of mutual inductance in terms of self inductance of the two coils L1 and L2 is proportional to
Pregunta 29
Pregunta
Coupling coefficient k, a term much used in radio work can be obtained from
Respuesta
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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
Respuesta
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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
Respuesta
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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
Pregunta 34
Pregunta
According to hysteresis law, hysteresis loss in a material is proportional to
Pregunta 35
Pregunta
A degaussing is the process of
Respuesta
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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