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