### questions

Title
###### An air gap is usually inserted in magnetic circuits to

An air gap is usually inserted in magnetic circuits to

1. increase m.m.f.
2. increase the flux
3. prevent saturation
4. none of the above
###### The relative permeability of a ferromagnetic material is

The relative permeability of a ferromagnetic material is

1. less than one
2. more than one
3. more than 10
4. more than 100 or 1000
###### The unit of magnetic flux is

The unit of magnetic flux is

1. henry
2. weber
3. ampereturn/weber
4. ampere/metre
###### Permeability in a magnetic circuit corresponds to______ in an electric circuit

Permeability in a magnetic circuit corresponds to______ in an electric circuit.

1. resistance
2. resistivity
3. conductivity
4. conductance
###### Point out the wrong statement.Magnetic leakage is undesirable in electric machines because it

Point out the wrong statement.Magnetic leakage is undesirable in electric machines because it

1. lowers their power efficiency
2. increases their cost of manufacture
3. leads to their increased weight
4. produces fringing
###### Relative permeability of vacuum is

Relative permeability of vacuum is

1. 1
2. 1 H/m
3. 1/4JI
4. 4n x 10-' H/m
###### Permanent magnets are normally made of

Permanent magnets are normally made of

1. alnico alloys
2. aluminium
3. cast iron
4. wrought iron
###### Energy stored by a coil is doubled when its current is increased by percent

Energy stored by a coil is doubled when its current is increased by percent.

1. 25
2. 50
3. 41.4
4. 100
###### Those magnetic materials are best suited for making armature and transformer coreswhich have____permeability and_______hystersis loss

Those magnetic materials are best suited for making armature and transformer coreswhich have____permeability and_______hystersis loss.

1. high, high
2. low, high
3. high, low
4. low, low
###### The rate of rise of current through an inductive coil is maximum

The rate of rise of current through an inductive coil is maximum

1. at 63.2% of its maximum steady value
2. at the start of the current flow
3. after one time constant
4. near the final maximum value of current
###### When both the inductance and resistance of a coil are doubled the value of

When both the inductance and resistance of a coil are doubled the value of

1. time constant remains unchanged
2. nitial rate of rise of current is doubled
3. inal steady current is doubled
4. time constant is halved
###### The initial rate of rise of current through a coil of inductance 10 H when suddenlyconnected to a D.C. supply of 200 V is_______Vs

The initial rate of rise of current through a coil of inductance 10 H when suddenlyconnected to a D.C. supply of 200 V is_______Vs

1. 50
2. 20
3. 0.05
4. 500
###### A material for good magnetic memory should have

A material for good magnetic memory should have

1. low hysteresis loss
2. high permeability
3. low retentivity
4. high retentivity
###### Conductivity is analogous to

Conductivity is analogous to

1. retentivity
2. resistivity
3. permeability
4. inductance
###### In a magnetic material hysteresis loss takes place primarily due to

In a magnetic material hysteresis loss takes place primarily due to

1. rapid reversals of its magnetisation
2. flux density lagging behind magnetising force
3. molecular friction
4. it high retentivity
###### Those materials are well suited for making permanent magnets whichhave______retentivity and _______coercivity

Those materials are well suited for making permanent magnets whichhave______retentivity and _______coercivity

1. low, high
2. high, high
3. high, low
4. low, low
###### If the area of hysteresis loop of a material is large, the hysteresis loss in this materialwill be

If the area of hysteresis loop of a material is large, the hysteresis loss in this materialwill be

1. zero
2. small
3. large
4. none of the above
###### Hard steel is suitable for making permanent magnets because

Hard steel is suitable for making permanent magnets because

1. it has good residual magnetism
2. its hysteresis loop has large area
3. its mechanical strength is high
4. its mechanical strength is low
###### Silicon steel is used in electrical machines because it has

Silicon steel is used in electrical machines because it has

1. low co-ercivity
2. low retentivity
3. low hysteresis loss
4. high co-ercivity
###### Conductance is analogous to

Conductance is analogous to

1. permeance
2. reluctance
3. flux
4. inductance

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