## electrical

### Magnetic Circuit MCQ Questions and Answers

1.
 An air gap is usually inserted in magnetic circuits to A Increase m.m.f B Increase the flux C Prevent saturation D None of the above Answer : C Explanation :
2.
 The relative permeability of a ferromagnetic material is A Less than one B More than one C More than 10 D More than 100 or 1000 Answer : D Explanation :
3.
 The unit of magnetic flux is A Henry B Weber C Ampere-turn/weber D Ampere/meter Answer : B Explanation :
4.
 Permeability of a magnetic circuit corresponds to………. In an electrical circuit A Resistance B Resistivity C Conductivity D Conductance Answer : C Explanation :
5.
 Point out the wrong statement. Magnetic leakage is undesirable inn electric machine because it A Lower their power efficiency B Increases their cost of manufacture C Leads to their increased weight D Produces fringing Answer : A Explanation :
6.
 The magnetising force (H) and magnetic flux density (B) are connected by the relation A B = µrH/µ0 B B = µH C B = H/µrµ0 D B = µr/Hµ0 Answer : B Explanation :
7.
 Permanent magnets are normally made of A Alnico alloys B Aluminium C Cast iron D Wrought iron Answer : A Explanation :
8.
 Energy stored by a coil is doubled when its current is increased by ………. percent. A 25 B 50 C 41.4 D 100 Answer : C Explanation :
9.
 Those magnetic materials are best suited for making armature and transformer cores which have …. permeability and …… hysteresis loss. A High, high B Low, high C High, Low D Low, Low Answer : C Explanation :
10.
 The rate of rise of current through an inductive coil is maximum A At 63.2% of its maximum steady value B At the start of the current flow C After one time constant D Near the final maximum value of current Answer : B Explanation :
11.
 When both the inductance and resistance of the coil are doubled the value of A Time constant remains unchanged B Initial rate of rise of current is doubled C Final steady current is doubled D Time constant is halved Answer : A Explanation :
12.
 The initial rate of rise of current through a coil of inductance 10H when suddenly connected to a D.C. supply of 200v is …… A/s A 50 B 20 C 0.05 D 500 Answer : B Explanation :
13.
 A material for good magnetic memory should have A Low hysteresis loss B High permeability C Low retentivity D High retentivity Answer : D Explanation :
14.
 Conductivity is analogous to A Retentivity B Resistivity C Permeability D inductance Answer : C Explanation :
15.
 In a magnetic material hysteresis loss takes place primarily due to A Rapid reversals of its magnetisation B Flux density lagging behind magnetising force C Molecular friction D It high retentivity Answer : D Explanation :
16.
 Those materials are well suited for making permanent magnets which have ……. retentivity and ………. Coercivity. A Low, high B High, high C High, low D Low, low Answer : B Explanation :
17.
 If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be A Zero B Small C Large D None of the above Answer : C Explanation :
18.
 Hard steel is suitable for making permanent magnets because A It has good residual magnetism B Its hysteresis loop has large area C Its mechanical strength is high D Its mechanical strength is low Answer : A Explanation :
19.
 Silicon steel is used in electrical machines because it has A Low co-ercivity B Low retentivity C Low hysteresis D High co-ercivity Answer : C Explanation :
20.
 Conductance is analogous to A Permanence B Reluctance C Flux D Inductance Answer : A Explanation :
21.
 The property of a material which opposes the creation of magnetic flux in int is known as A Reluctivity B Magnetomotive force C Permeance D Reluctance Answer : D Explanation :
22.
 The unit of retentivity is A Weber B Weber/sq.m C Ampere turn/metre D Ampere turn Answer : B Explanation :
23.
 Reciprocal of reluctance is A Reluctivity B Permanence C Permeability D Susceptibility Answer : B Explanation :
24.
 While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit? A E.m.f B Current C Current density D Conductivity Answer : B Explanation :
25.
 The unit of reluctance is A Metre/henry B Henry/metre C Henry D 1/henry Answer : D Explanation :
26.
 A ferrite core has less eddy current loss than an iron core because A Ferrites have high resistance B Ferrites are magnetic C Ferrites have low permeability D Ferrites have high hysteresis Answer : D Explanation :
27.
 A ferromagnetic core subjected to cycles of magnetisation will exhibit hysteresis when the cycle is A Rotating B Alternating C Pulsating D Any of the above Answer : D Explanation :
28.
 In order to minimise loss due to hysteresis, the magnetic material should have A High resistivity B Low hysteresis is co-efficient C Large B-H loop area D High retentivity Answer : B Explanation :
29.
 Hysteresis loss least depends on A Volume of material B Frequency C Steinmetz co-efficient of material D Ambient temperature Answer : D Explanation :
30.
 Laminated cores, in electrical machines are used to reduce A Copper loss B Eddy current loss C Hysteresis loss D All of the above Answer : B Explanation :
31.
 The area of hysteresis loss is a measure of A Permittivity B Permeance C Energy loss per cycle D Magnetic flux Answer : C Explanation :
32.
 Permeance is to reluctance as conductance is to A Ampere turns B Inductance C Capacitance D Resistance Answer : D Explanation :
33.
 According to steinmetz hysteresis law, hysteresis loss in a material is proportional to A B 3.6 B B1.6 C B1.2 D B2.6 Answer : B Explanation :
34.
 The transformer cores operating at microwave frequency range, are usually made of A Carbon B Copper C Silicon steels D Ferrites Answer : D Explanation :