Quiz sheet for magnetic circuits

A material of low reluctance:

A) may be machined easily

B) has a low reactance

C) has a low permeability

D) has a high permeability

ANSWER: D

If an air gap is introduced into a magnetic circuit the total flux in the magnetic circuit is:

A) reduced to zero

B) increased to saturation

C) reduced, depending on the gap width

D) unchanged

ANSWER: C

Reluctance is the magnetic equivalent of which electrical unit:

A) voltage

B) current

C) reactance

D) resistance

ANSWER: D

The small amount of magnetism that is retained by iron on removal of a magnetising force is termed: 

A) residing magnetism

B) residual magnetism

C) permeability

D) saturation

ANSWER: B

The term saturation used in B-H curves means that for a further increase in magnetising force will result in: 

A) very little increase in flux density

B) a large change in flux density

C) a large linear change in flux density

D) the flux density will decrease

ANSWER: A

The type of magnet created when a coil of wire wound around a bar of steel is:

A) A horseshoe magnet

B) A permenant magnet

C) A bar magnet

D) An electromagnet

ANSWER: D

The unit of flux density is: 

A) henry

B) ampere turn

C) ampere turn per metre

D) tesla

ANSWER: D

The unit of flux density is the:

A) Ampere

B) Volt

C) Tesla

D) Weber

ANSWER: C

The unit of magnetomotive force is the: 

A) henry

B) tesla

C) ampere turn

D) ampere turns per metre

ANSWER: C

When using the right hand  rule for conductors, the thumb indicates: 

A) direction of voltage

B) south pole

C) direction of current

D) north pole

ANSWER: C

Magnetic screening may be provided by using:

A) manganin

B) iron

C) copper

D) glass

ANSWER: B

The point at which saturation starts to occur on the magnetisation curve is known as the:

A) linear point

B) peak flux density

C) bend

D) knee

ANSWER: D

Soft iron is often used for direct current electromagnetic cores because it:

A) has low retentivity

B) has zero reluctance

C) is cheap

D) has low permeability

ANSWER: A

The strength of the magnetic flux of a solenoid is proportional to:

A) permeability, turns and current

B) resistivity, turns and current

C) reluctance, permeability and current

D) magnetising force, turns and reluctance

ANSWER: A

Hysteresis loss is due to:

A) residual magnetism

B) high reluctance 

C) low permeability

D) excessive flux density

ANSWER: A

In reference to a hysteresis loop, another name for residual magnetism is:

A) coercive magnetism

B) temporary magnetism

C) permanent magnetism

D) remanent magnetism

ANSWER: D

Residual magnetism may cause d.c. relays to:

A) overheat

B) remain closed when de-energised

C) chatter

D) remain open when the supply is switched on.

ANSWER: B

Saturation of a magnetic material means that any further increase in the magnetomotive force will:

A) cause the material to overheat

B) result in a small increase in magnetic flux within the material

C) reduce the magnetic flux within the material

D) make the material act as a magnetic screen

ANSWER: B

A B-H curve shows how the flux density changes due to the.

A) magnetising force

B) material reluctance

C) flux

D) reluctance

ANSWER: A

Change in number of magnetic field lines induces

A) EMF in the coil

B) current in coil

C) frequency in coil

D) both current and frequency

ANSWER: A

Flux density is a measure of the amount of:

A) magnetic flux per unit area.

B) magnetic flux.

C) reluctance per unit area.

D) inductance flux per unit area.

ANSWER: A

The direction of the magnetic field around a single current carrying conductor can be determined by:

A) the right hand conductor rule.

B) Fleming's right hand rule.

C) Fleming's left hand rule.

D) the right hand solenoid rule

ANSWER: A

Direction of induced emf in a circuit is in accordance with law of

A) conservation of energy

B) conservation of mass

C) conservation of charge

D) conservation of momentum

ANSWER: A

Force on a wire inside magnetic field increase when

A) current is increased

B) current is constant

C) current is changing

D) current decreased

ANSWER: A

If coil is placed perpendicular to field lines then number of lines passing through coil are

A) maximum

B) minimum

C) zero

D) may be max. or min

ANSWER: A

The lagging of changes in magnetic flux density behind changes in magnetising force is known as:

A) hysterisis

B) permitivity

C) eddy current loss

D) reluctance

ANSWER: A

______ occurs when the flux density of a material cannot be increased further for increases in magnetising force.

A) Saturation

B) Retentivity

C) Coercive force

D) Residual magnetism

ANSWER: A

Direction of induced current always

A) opposes the cause

B) remains same as that of cause

C) equal to cause that produces it

D) directs the cause

ANSWER: A

Last modified: Tuesday, 1 June 2021, 9:38 AM