In electro-mechanical conversion devices like generators and motors the reason why a small air gap is left between the rotor and stator is to
permit mechanical clearance
increase flux density in air gap
decrease the reluctance of magnetic path
complete the magnetic path
Correct Answer :
A. permit mechanical clearance
Related Questions
The hot resistance of an incandescent lamp is about _______ its cold resistance.
10 times
100 times
5 times
50 times
There are how many compounds available in nature?
300a000
Unlimited
The greater percentage of materials is _________.
diamagnetic
paramagnetic
ferromagnetic
non-magnetic
Defined as the flux density produced in it due to its own induced magnetism
Magnetic field intensity
Electric field intensity
Electromagnetic field intensity
Intensity magnetization
The electric field intensity between the parallel plate air capacitor is 20 N/C. If an insulating slab of relative permittivity 5 is placed between the platesa then electric field intensity will be
20 N/C
100 N/C
4N/C
40 N/C
When a wire loop is rotated in a magnetic field the direction of the induced emf changes one in every _______ revolution
Electromotive force in a circuit
causes free electrons to flow
increases the circuit resistance
maintains circuit resistance
is needed to make the circuit complete
Magnetic intensity is a
Phasor quantity
Physical quantity
Scalar quantity
Vector quantity
Calculate the permeability (in T/A. t/m) of a magnetic material that has a relative permeability of 300
3.78 x 10^4
3.78 x 10^-5
3.78 x 10^-3
3.78 x 10^-6
The potential at a point due to a charge is 15 V. If the distance is times, the potential at the point will be
5 V
18 V
45 V
15 V
Electric potential is a _______ quantity.
scalar
phasor
vector
variable
Three charges of +5 Ca -6 C and +9 C are placed inside a sphere. What is the total flux passing through the surface of sphere?
8 C
14 C
20 C
-6 C
What principle states that each electron in an atom must have a different set of quantum numbers?
Inclusion principle
Exclusion principle
Quantum principle
Electron principle
What is the relative permittivity of air?
8.854 × 10^-12
4 × 10^7
If the number of valence electrons of an atom is less than 4a the substance is called
a conductor
a semiconductor
an insulator
a superconductor
The process by which an emf and hence current is generated or induced in a conductor when there is a change in the magnetic flux linking the conductor is called
Electromagnetic induction
Mutual induction
Faraday's law
Electromagnetic interference
If the right handed bottle-opener cork screw is assumed to be along the conductor so as to advance in the direction of current flow, the motion of its handle will indicate the direction of magnetic flux produced around the conductor. This is known as
Right hand rule
Left hand rule
Cork screw rule
End rule
The electric flux density is a ________ quantity.
phasor
vector
scalar
variable
The conduction of electricity across the surface of a dielectric is called
creepage
skin effect
surface effect
crosstalk
Which of the following is a natural magnet?
Steel
Magnesia
Lodestone
S oft iron
If you hold the conductor with right hand so that the stretched thumb points in the direction of the currenta then encircling fingers will give the direction of magnetic lines of force round the conductor. This is known as
Left hand cork screw rule
Right hand cork screw rule
Left hand rule
Right hand rule
Which of the following is a paramagnetic material?
Carbon
Copper
Bismuth
Oxygen
If a 20 V potential is applied across a relay coil with 50 turns having 1 ? of resistancea the total magnetomotive producing magnetic flux in the circuit is
10 Wb
50 T
1000 A t/m
1000,t
If on looking at any one end of a solenoid; the direction of current flow is found to be clockwise then the end under observation is a south pole. This is known as
Right hand rule
Left hand rule
Cork screw rule
End Rule
Electric field intensity is a ________.
scalar
phasor
vector
variable
The electric potential at a point in air due to a charge is 21 V. If the air is replaced by a medium of relative permittivity of 3a then electric potential at that point will be
63 V
21 V
7 V
42 V
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Soft magnetic materials
Hard magnetic materials
High hysteresis loss materials
Low hysteresis loss materials
If the value of 25 of a conductor is 1/230 per oCa then the value of 0is
1/180 peroC
1/150 per oC
1/280 per oC
1/230 per oC
A law that states that the polarity of the induced voltage will oppose the change in magnetic flux causing the induction.
Joule's law
Faraday's law
Coulomb's law
Lenz' law
One that has magnetic poles produced by internal atomic structure with no external current necessary
Diamagnetic
Permanent magnets
Paramagnetic
Electromagnetic