Free Electrical Machines MCQs with Answers

• A. copper
• B. aluminium
• C. soft iron
• D. brass

Explanation: Soft iron has high permeability, so it provides an easy path for magnetic flux and diverts the field away from the screened region.

• A. Kirchhoffs law
• B. Lenz's law
• C. Ampere's law
• D. Faraday's laws

Explanation: Ampère's law relates current to the magnetic field around it, while the Biot-Savart law gives the field contribution from each small…

• A. less than that of disc but in opposite direction
• B. equal to that of disc and in the same direction
• C. equal to that of disc and in the opposite direction
• D. less than that of disc and in the same direction

Explanation: The rotating copper disc produces eddy currents whose magnetic field opposes the relative motion of the needle.

• A. 2
• B. 4
• C. 6
• D. 8

Explanation: Ampere-turns equal NI, so the current is I = 3200/800 = 4 A. The correct value is therefore option b.

• A. ferromagnetic
• B. paramagnetic
• C. diamagnetic
• D. dielectric

Explanation: Diamagnetic materials have relative permeability slightly below unity, so they conduct magnetic flux slightly less readily than air.

• A. permanent magnets
• B. transformers
• C. non-magnetic substances
• D. electromagnets

Explanation: Retentivity is the ability to retain magnetism after the magnetising field is removed, which is essential for permanent magnets.

• A. attracts some substances and repels others
• B. attracts all paramagnetic substances and repels others
• C. attracts only ferromagnetic substances
• D. attracts ferromagnetic substances and repels all others

Explanation: A permanent magnet attracts magnetic substances such as iron and can repel another magnet when like poles face each other.

• A. diamagnetic
• B. paramagnetic
• C. ferromagnetic
• D. insulating

Explanation: Ferromagnetic materials have a strongly field-dependent permeability because their magnetic domains align and later become nonlinear or…

• A. loud-speakers
• B. generators
• C. motors
• D. all of the above

Explanation: Temporary magnets are electromagnets whose magnetism exists mainly while current flows, making them useful in loudspeakers, generators…

• A. strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force
• B. uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts
• C. both of above
• D. none of the above

Explanation: Solenoid noise can result from magnetic pull and repulsion that make laminations fan out, or from uneven bearing surfaces caused by dirt…

• A. by means of a small auxiliary motor
• B. from AC. side as induction motor
• C. from D.C. side as D.C. motor
• D. any of the above methods
• E. none of the above methodsHire Civil Engineers

Explanation: A synchronous converter has no inherent starting torque, so it may be brought up to speed by an auxiliary motor or started through its AC…

• A. two
• B. three
• C. four
• D. six
• E. noneTry Prep Courses

Explanation: A single-phase rotary converter receives single-phase AC through two slip rings, while its commutator supplies DC.

• A. an induction motor and a D.C. generator
• B. a synchronous motor and a D.C. generator
• C. a D.C. series motor and a D.C. generator
• D. none of the aboveCompare Home Electronics

Explanation: A rotary converter is essentially a synchronous motor and a DC generator combined on one armature and shaft.

• A. Motor generator set
• B. Motor converter
• C. Rotary converter
• D. Any of the above
• E. None of the above

Explanation: A rotary converter can work in reverse, accepting DC through its commutator and delivering AC through its slip rings.

• A. one armature and one field
• B. two armatures and one field
• C. one armature and two fields
• D. none of the above

Explanation: A rotary converter uses one armature carrying both the AC and DC windings, with one field system producing the magnetic flux.

• A. a transformer
• B. an induction motor
• C. an alternator
• D. any D.C. machine

Explanation: Its rotating armature, field system and commutator make a rotary converter structurally similar to a DC machine.

• A. low power factor
• B. high power factor
• C. zero power factor
• D. none of the above

Explanation: A rotary converter normally operates with a high power factor, especially when its excitation is properly adjusted.

• A. d.c. only
• B. a.c. only
• C. partly a.c. and partly d.c.

Explanation: The armature conductors carry alternating currents in the armature winding, while the commutator makes the external DC current…

• A. Synchronous motor
• B. Squirrel cage induction motor
• C. Slip ring induction motor
• D. Any of the above

Explanation: A synchronous motor is commonly used to drive large motor-generator sets because it operates at constant speed and can provide high…

• A. same
• B. less
• C. double
• D. three times

Explanation: A rotary converter performs conversion with fewer armature windings and generally has lower copper resistance than a DC generator of…