### 1.An air gap is usually inserted in magnetic circuits to

• AIncrease m.m.f
• BIncrease the flux
• CPrevent saturation
• DNone of the above

Prevent saturation

Explanation:

An air gap is usually inserted in magnetic circuits to Prevent saturation.

### 2.The relative permeability of a ferromagnetic material is

• ALess than one
• BMore than one
• CMore than 10
• DMore than 100 or 1000

More than 100 or 1000

Explanation:

The relative permeability of a ferromagnetic material is More than 100 or 1000.

### 3.The unit of magnetic flux is

• AHennery
• BWeber
• CAmpere-turn/weber
• DAmpere/meter

Weber

Explanation:

The unit of magnetic flux is Weber.

### 4.Permeability of a magnetic circuit corresponds to____________ In an electrical circuits.

• AResistance
• BResistivity
• CConductivity
• DConductance

Conductivity

Explanation:

### 5.Point out the wrong statement.Magnetic leakage is undesirable inn electric machine because it

• ALower their power efficiency
• BIncreases their cost of manufacture
• CLeads to their increased weight
• DProduces fringing

Lower their power efficiency

Explanation:

### 6.Permanent magnets are normally made of

• AAlnico alloys
• BAluminium
• CCast iron
• DWrought iron

Alnico alloys

Explanation:

Permanent magnets are normally made of Alnico alloys.

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

• A25
• B50
• C41.4
• D100

41.4

Explanation:

Energy stored by a coil is doubled when its current is increased by 41.4 percent.

### 8.Those magnetic materials are best suited for making armature and transformer cores should have

• AHigh permeability, high hysteresis loss
• BLow permeability, high hysteresis loss
• CHigh permeability, Low hysteresis loss
• DLow permeability, Low hysteresis loss

High permeability, Low hysteresis loss

Explanation:

Those magnetic materials are best suited for making armature and transformer cores should have High permeability, Low hysteresis loss.

### 9.The rate of rise of current through an inductive coil is maximum

• AAt 63.2% of its maximum steady value
• BAt the start of the current flow
• CAfter one time constant
• DNear the final maximum value of current

At the start of the current flow

Explanation:

The rate of rise of current through an inductive coil is maximum At the start of the current flow.

### 10.When both the inductance and resistance of the coil are doubled the value of

• ATime constant remains unchanged
• BInitial rate of rise of current is doubled
• CFinal steady current is doubled
• DTime constant is halved

Time constant remains unchanged

Explanation:

When both the inductance and resistance of the coil are doubled the value of Time constant remains unchanged.

• A50
• B20
• C0.05
• D500

20

Explanation:

### 12.A material for good magnetic memory should have

• ALow hysteresis loss
• BHigh permeability
• CLow retentivity
• DHigh retentivity

High retentivity

Explanation:

A material for good magnetic memory should have High retentivity.

### 13.Conductivity is analogous to

• ARetetnivity
• BResistivity
• CPermeability
• Dinductance

Permeability

Explanation:

### 14.In a magnetic material hysteresis loss takes place primarily due to

• ARapid reversals of its magnetization
• BFlux density lagging behind magnetising force
• CMolecular friction
• DIt's high retentivity

It's high retentivity

Explanation:

In a magnetic material hysteresis loss takes place primarily due to It's high retentivity.

### 15.Those materials are well suited for making permanent magnets should have

• ALow retentivity, high Coercivity
• BHigh retentivity, high Coercivity
• CHigh retentivity, low Coercivity
• DLow retentivity, low Coercivity

High retentivity, high Coercivity

Explanation:

Those materials are well suited for making permanent magnets should have High retentivity, high Coercivity.

### 16.If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be

• AZero
• Bsmall
• CLarge
• DNone of the above

Large

Explanation:

If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be Large.

### 17.Hard steel is suitable for making permanent magnets because

• AIt has good residual magnetism
• BIts hysteresis loop has large area
• CIts mechanical strength is high
• DIts mechanical strength is low

It has good residual magnetism

Explanation:

Hard steel is suitable for making permanent magnets because It has good residual magnetism.

### 18.Silicon steel is used in electrical machines because it has

• ALow co-ercivity
• BLow retentivity
• CLow hysteresis
• DHigh co-ercivity

Low hysteresis

Explanation:

Silicon steel is used in electrical machines because it has Low hysteresis.

• Aq
• Bq
• Cq
• Dq

q

Explanation:

• APermanence
• BReluctance
• CFlux
• DInductance