In this article, we shared the electromagnetism objective questions and answers for electrical and electronics engineers.
Electromagnetism Objective Questions
The below list provides all the multiple-choice questions related to electromagnetism.
Answers are available at the bottom of the article.
1. Which of the following is a vector quantity?
| A) | Magnetic potential |
| B) | Magnetic field intensity |
| C) | Flux density |
| D) | Relative permeability |
2. What is the value of the magnetic vector potential due to an infinitesimally small current element, evaluated at an infinite distance from it?
| A) | Unity. |
| B) | Infinity. |
| C) | Any number between zero and infinity depends on the strength of the current element. |
| D) | Zero. |
3. A permanent magnet
| A) | attracts some substances and repels others |
| B) | attracts only ferromagnetic substances |
| C) | attracts ferromagnetic substances and repels all others |
| D) | attracts all paramagnetic substances and repels others |
4. Reciprocal of reluctance is
| A) | permeance |
| B) | susceptibility |
| C) | permeability |
| D) | reluctivity |
5. In a magnetic material, hysteresis loss takes place primarily due to
| A) | rapid reversal of its magnetization. |
| B) | flux density lagging behind the magnetizing force. |
| C) | It’s high retentivity. |
| D) | molecular friction. |
6. The magnitude of induced emf in a conductor depends upon the
| A) | the flux density of their magnetic field. |
| B) | rate of change of flux linkage. |
| C) | amount of flux cut. |
| D) | amount of flux linkage. |
7. The magnetic field strength of an air-cored coil can be increased by
| A) | increasing the core x-sectional area. |
| B) | increasing the number of turns on the coil. |
| C) | increasing the current strength. |
| D) | any of these answers |
| E) | inserting a soft iron core into the coil. |
8. The uniform magnetic field is
| A) | none of these answers |
| B) | the field of a single conductor |
| C) | the field of a set of parallel conductors |
| D) | the field in winch all lines of magnetic flux are parallel and equidistant |
9. Laminated cores in electrical machines are used to reduce
| A) | copper loss |
| B) | hysteresis loss |
| C) | all of these answers |
| D) | eddy current loss |
10. Tesla is a unit of
| A) | flux density |
| B) | field strength |
| C) | flux |
| D) | inductance |
11. Hysteresis loss least depends on
| A) | frequency. |
| B) | volume of material |
| C) | Steinmetz coefficient of the material |
| D) | ambient temperature |
12. The hysteresis loss is caused by
| A) | structural non-homogeneity. |
| B) | potential work function. |
| C) | none of these answers |
| D) | work required for magnetising the material. |
13. Energy stored by a coil is doubled when its current is increased by
| A) | 100 percent. |
| B) | 50 percent. |
| C) | 35 percent. |
| D) | 41.4 percent. |
14. When a plane wave propagates in a dielectric medium
| A) | The net average energy density is finite. |
| B) | The average electric energy density is not dependent on the average magnetic energy density |
| C) | The average electric energy and the average magnetic energy densities are equal. |
| D) | The average electric energy and the average magnetic energy densities are not equal. |
15. In which of the materials the spin moments associated with two sets of atoms are aligned antiparallel to each other?
| A) | Antiferromagnetic materials |
| B) | Ferromagnetic materials |
| C) | Ferriimagnetic materials |
| D) | Ferrites |
16. The tubes of force within the magnetic material are known as
| A) | lines of force |
| B) | electric flux |
| C) | none of these answers |
| D) | tubes of induction |
17. Which of the following is a ferromagnetic material?
| A) | Nickel |
| B) | Aluminium |
| C) | Copper |
| D) | Tungsten |
18. The direction of magnetic lines of force is
| A) | from south pole to north pole |
| B) | none of these answers |
| C) | from one end of the magnet to another |
| D) | from north pole to south pole |
19. The magnetic reluctance of a material
| A) | does not vary with increasing cross-sectional area of material |
| B) | increases with an increasing cross-sectional area of material |
| C) | any of these answers |
| D) | decreases with increasing cross-sectional area of material |
20. Degaussing is the process of
| A) | remagnetising metallic parts |
| B) | removing gases from the materials |
| C) | removal of magnetic impurities |
| D) | demagnetising metallic parts |
21. A conductor of length L has current I passing through it when it is placed parallel to a magnetic field. The force experienced by the conductor will be
| A) | BIL |
| B) | BL2I |
| C) | BI2L |
| D) | zero |
22. If the area of the hysteresis loop of a material is large, the hysteresis loss in this material will be
| A) | none of these answers |
| B) | large |
| C) | small |
| D) | zero |
23. While comparing magnetic and electric circuits, the flux of the magnetic circuit is compared with which parameter of the electrical circuit?
| A) | Current |
| B) | Conductivity |
| C) | Current density |
| D) | E.m.f. |
24. Two coils are coupled in such a way that the mutual inductance between them is 16 mH. If the inductances of the coils are 20 mH and 80 mH respectively, the coefficient of coupling is
| A) | 0.01 |
| B) | 0.1 |
| C) | 0.0025 |
| D) | 0.4 |
25. According to steinmetz hysteresis law, hysteresis loss in a material is proportional to
| A) | B1.6 |
| B) | B3.6 |
| C) | B2.6 |
| D) | B1.2 |
26. A magnet does not attract
| A) | iron |
| B) | copper |
| C) | nickel |
| D) | cobalt |
27. In a simple magnetic field the strength of magnet flux
| A) | increases continuously from initial value to final value |
| B) | first increases and then decreases till it becomes zero |
| C) | decreases continuously from initial value to final value |
| D) | is constant and has same value in energy part of the magnetic field |
28. An air gap is usually inserted in magnetic circuits so as to
| A) | prevent saturation. |
| B) | increase in flux. |
| C) | increase in mmf. |
| D) | increase in inductance. |
29. For a perfect conductor, the field strength at a distance equal to the skin depth is X% of the field strength at its surface. The value of ‘X%’ is
| A) | Zero |
| B) | 26 % |
| C) | 50 % |
| D) | 36 % |
30. Consider the following statements:
In the case of diamagnetic materials, the magnetic susceptibly is
1. positive.
2. negative.
3.independent of temperature.
4.inversely proportional to temperature.
Of these statements
| A) | 2 and 3 are correct. |
| B) | 1 and 4 are correct. |
| C) | 2 and 4 are correct. |
| D) | 1 and 3 are correct. |
31. A ferrite core has less eddy current loss than an iron core because
| A) | ferrites are magnetic |
| B) | ferrites have high resistance |
| C) | ferrites have high hysteresis |
| D) | ferrites have low permeability |
32. Core of an electromagnet should have
| A) | low coercivity |
| B) | both high susceptibility & low coercivity |
| C) | none of these answers |
| D) | high susceptibility |
33. In a magnetic material hysteresis loss takes place primarily due to
| A) | flux density lagging behind magnetising force |
| B) | molecular friction |
| C) | rapid reversals of its magnetisation |
| D) | it high retentivity |
34. Iron is a
| A) | antifenomagnetic material. |
| B) | ferrimagnetic. |
| C) | ferromagnetic. |
| D) | paramagentic. |
35. If a copper conductor is moved across a magnetic field
| A) | the wire will become magnetic |
| B) | nothing will happen |
| C) | a voltage will be induced in the wire. |
| D) | a current will be induced in the wire |
36. Permeance is to reluctance as conductance is to
| A) | inductance |
| B) | resistance |
| C) | ampere turns |
| D) | capacitance |
37. The electromagnet is made of
| A) | any of these answers |
| B) | steel core. |
| C) | soft iron core wrapped in a coil of fine wire with current flowing through it. |
| D) | soft iron core. |
38. Those magnetic materials are best suited for making armature and transformer cores which have____ permeability and____ hystersis loss.
| A) | high, high |
| B) | low, low |
| C) | high, low |
| D) | low, high |
39. The commonly used material for shielding or screening magnetism is
| A) | soft iron |
| B) | copper |
| C) | brass |
| D) | aluminium |
40. How does the. magnetic compass needle behave in a magnetic field?
| A) | lt assures a position which follows a line of magnetic flux |
| B) | It starts rotating |
| C) | None of these answers |
| D) | It assures a position right angle to magnetic field |
41. The bar magnet has
| A) | none of these answers |
| B) | both monopole moment and dipole moment. |
| C) | dipole moment. |
| D) | monopole moment. |
42. The shape of B-H curve for air gap is
| A) | ellipse. |
| B) | parabola. |
| C) | sinusoidal. |
| D) | straight line. |
43. Out of the following statements, concerning an electric field, which statement is not true ?
| A) | The electric intensity is vector quantity |
| B) | Unit field intensity in the exertion of a force of one newton on a charge of one coulomb |
| C) | The electric field intensity at a point is numerically equal to the force exerted upon a charge placed at that point |
| D) | M electric field is defined as a point in space at which an electric charge would experience a force |
44. The surface integral of the electrical field intensity is the
| A) | flux density. |
| B) | net flux emanating from the surface. |
| C) | electric charge. |
| D) | charge density. |
45. The main constituent of permalloy is
| A) | cobalt |
| B) | tungsten |
| C) | nickel |
| D) | chromium |
46. Two coils having equal resistances but different inductances are connected in series.
The time constant of the series combination is the
| A) | sum of the time constant of the individual coils. |
| B) | average of the time constants of the individual coils. |
| C) | product of the time constants of the individual coils. |
| D) | geometric mean of the time constants of the individual coils. |
47. Ferrites are a sub-group of
| A) | ferro-magnetic materials |
| B) | ferri-magnetic materials |
| C) | non-magnetic materials |
| D) | paramagnetic materials |
48. The property of a material which opposes the production of magnetic flux in it is known as
| A) | permittivity. |
| B) | permeance. |
| C) | mmf. |
| D) | reluctance. |
49. Conductance is analogous to
| A) | permeance |
| B) | flux |
| C) | inductance |
| D) | reluctance |
50. The magnetising force (H) and magnetic flux density (B) are connected by the relation
| A) | B = μrH/μ0 |
| B) | B = H/μ0μr |
| C) | B = μ0H/μr |
| D) | B = μH |
51. Conductivity is analogous to
| A) | resistivity |
| B) | permeability |
| C) | inductance |
| D) | retentivity |
52. The unit of magnetic flux is
| A) | ampere-turn/weber |
| B) | weber |
| C) | henry |
| D) | ampere/metre |
53. Supermagnetic materials are composed of
| A) | none of these answers |
| B) | ferromagnetic particles in ferromagnetic matrix |
| C) | non-ferromagnetic particles in paramagnetic matrix |
| D) | ferromagnetic particles in a nonferromagnetic matrix |
54. Which of the following statements should be true if one compares the hysteresis loops of hard and soft magnetic materials?
1. Hysteresis loss of hard magnetic material will be less than that of soft material.
2. Coercivity of hard material will be greater than that of soft material.
3. Retentivity of two materials will always be equal.
Select the correct answer using the codes given below Codes:
| A) | 2 and 3 |
| B) | 1, 2 and 3 |
| C) | 2 alone |
| D) | 1 alone |
55. The use of permanent magnets is not made in
| A) | energy meters |
| B) | transformers |
| C) | loud-speakers |
| D) | magnetoes |
56. What is the value of total electric flux coming out of a closed surface?
| A) | Zero. |
| B) | Equal to the surface charge density. |
| C) | Equal to volume charge density. |
| D) | Equal to the total charge enclosed by the surface. |
57. According to Faraday’s law of electromagnetic induction an emf is induced in a conductor whenever it
| A) | cuts the magnetic flux. |
| B) | lies in a magnetic field. |
| C) | moves parallel to the direction of magnetic field. |
| D) | lies perpendicular to the magnetic field. |
58. A certain amount of current flows through a ring-shaped coil with a fixed number of turns.
How does the magnetic induction B varies inside the coil if an iron core is threaded into coil without dimensional change of coil?
| A) | Decreases |
| B) | Increases |
| C) | Remains same |
| D) | First increases and then decreases depending on the depth of iron insertion |
59. Two long parallel conductors carry 100 A. If the conductors are separated by 20 mm, the force per meter of length of each conductor will be
| A) | 0.1 N |
| B) | 1 N |
| C) | 10 N |
| D) | 100 N |
60. Magnetostriction is a phenomenon of
| A) | generation of electricity in ferromagnetic materials |
| B) | generation of magnetism in conductors |
| C) | change in permeability of ferromagnetic materials during magnetization. |
| D) | change in physical dimensions of ferromagnetic materials during magnetization |
61. The magnetic susceptibility of a paramagnetic material is
| A) | equal to zero. |
| B) | less than zero. |
| C) | greater than one. |
| D) | less than one but positive. |
62. The principle of dynamically induced emf is utilized in a
| A) | thermocouple. |
| B) | transformer. |
| C) | choke. |
| D) | generator. |
63. Two parallel wires separated by a distance dare carrying a current in the same direction. The magnetic field along a line running parallel to these wires and midway between them
| A) | depends upon the permeability of medium between the wires |
| B) | depends upon I. |
| C) | depends upon d. |
| D) | is zero. |
64. A coil with a certain number of turns has a specified time constant. If the number of turns is doubled, its time constant would
| A) | become doubled. |
| B) | get halved. |
| C) | become four fold. |
| D) | remain unaffected. |
65. For which of the following materials the net magnetic moment should be zero?
| A) | Diamagnetic materials |
| B) | Antiferrimagnetic materials |
| C) | Antiferromagnetic materials |
| D) | Ferrimagnetic materials |
66. A 300 mm long conductor is carrying a current of 10 A and is situated at right angles to a magnetic field having a flux density of 0.8 T the force on the conductor will be
| A) | 0.24 N |
| B) | 2.4 N |
| C) | 240 N |
| D) | 24 N |
67. The unit of retentivity is
| A) | weber/sq. m |
| B) | weber |
| C) | ampere turn/metre |
| D) | ampere turn |
68. Which of the following statements is correct?
| A) | The magnetic flux inside the exciting coil is the same as on its outer surface |
| B) | The magnetic flux inside the exciting coil is greater than that on its outside surface. |
| C) | The magnetic flux inside an exciting coil is zero. |
| D) | The magnetic flux inside the exciting coil is lower than that on the outside surface. |
69. Which of the following is not a unit of flux?
| A) | Maxwell |
| B) | Weber |
| C) | Telsa |
| D) | All of these answers |
70. The unit of relative permeability is
| A) | it is dimensionless |
| B) | henry/metre |
| C) | henry/sq. m |
| D) | henry |
71. A coil wound over an iron ring carries a certain current and establishes flux in the ring. If the area of the x-section of the ring is doubled, the flux density in the core
| A) | is double of the previous value. |
| B) | is half of the previous value. |
| C) | is not possible to predict. |
| D) | is same as the previous value. |
72. Reluctance offered by the magnetic circuit depends upon
| A) | the cross-sectional area of the material. |
| B) | nature of magnetic material. |
| C) | length of magnetic flux path |
| D) | all of these answers |
73. Which of the following materials are diamagnetic?
| A) | Copper |
| B) | Iron |
| C) | Silver and copper |
| D) | Silver |
74. Remanent magnetism is one which
| A) | is left in the iron piece after the removal of the magnetic field. |
| B) | is produced by the superconductor coils. |
| C) | is produced by induction. |
| D) | is produced by electric current. |
75. The coupling between two magnetically coupled coils is said to be ideal if the coefficient of coupling is
| A) | 1 |
| B) | zero |
| C) | 2 |
| D) | 0.1 |
76. Which law is synonymous to the occurrence of diamagnetism?
| A) | Ampere’s law. |
| B) | Coulomb’s law. |
| C) | Lenz’s law. |
| D) | Maxwell’s law. |
77. The conductance of an electrical circuit is analogous to the magnetic circuit by
| A) | relative permeability. |
| B) | reluctance. |
| C) | permeance. |
| D) | flux. |
78. The magnetism left in the iron after the exciting field has been removed is known as
| A) | reluctance |
| B) | susceptance |
| C) | residual magnetism |
| D) | permeance |
79. The magnetic materials exhibit the property of magnetization due to
| A) | spin of electrons. |
| B) | orbital motion of electrons. |
| C) | all of these answers |
| D) | spin of nucleus. |
80. Magnetostriction is a phenomenon whereby the magnetization of a ferromagnetic material leads to a change in
| A) | physical dimensions |
| B) | magnetic susceptibility |
| C) | relative permeability |
| D) | spontaneous magnetization |
81. The unit of flux is the same as that of
| A) | resistance |
| B) | permeance |
| C) | pole strength |
| D) | reluctance |
82. Which of the following is correct?
| A) | B = µ0 H + M |
| B) | B = µ0 (H + M) |
| C) | B = M/µ0 |
| D) | B = µ0 M + H |
83. The rate of rise of current through an inductive coil is maximum
| A) | at 63.2% of its maximum steady value |
| B) | after one time constant |
| C) | near the final maximum value of current |
| D) | at the start of the current flow |
84. The most effective and quickest way of making a magnet from soft iron is by
| A) | placing it inside a coil carrying current |
| B) | the use of a permanent magnet |
| C) | rubbing with another magnet |
| D) | induction |
85. Air exhibits
| A) | antiferromagnetism. |
| B) | paramagnetism. |
| C) | ferromagnetism. |
| D) | ferromagnetic. |
86. When both the inductance and resistance of a coil are doubled the value of
| A) | initial rate of rise of current is doubled |
| B) | time constant remains unchanged |
| C) | final steady current is doubled |
| D) | time constant is halved |
87. Δ x E = dB/dt is derived from
| A) | none of these answers |
| B) | Faraday’s law. |
| C) | Ampere’s law. |
| D) | Gauss’s law. |
88. Which of the following type of materials are not very important for engineering applications?
| A) | Ferromagnetic |
| B) | Paramagnetic |
| C) | None of these answers |
| D) | Diamagnetic |
89. The magnitude of the force acting on a current-carrying conductor placed in a magnetic field is independent of
| A) | flux density. |
| B) | cross-sectional area of conductor. |
| C) | length of conductor. |
| D) | current flowing through the conductor. |
90. An electric field is parallel but opposite to a magnetic field. Electrons with some initial velocity enter the region of the fields at an angle θ along the direction of the electric field. The electron path will be
| A) | helical. |
| B) | elliptical. |
| C) | circular. |
| D) | straight. |
91. Energy stored by a coil is doubled when its current is increased by____ percent.
| A) | 50 |
| B) | 100 |
| C) | 25 |
| D) | 41.4 |
92. When a battery of E volts is suddenly applied across an ideal inductance of L henry, the current through inductance will be
| A) | increasing linearly at the rate of E/L ampere/s. |
| B) | none of these answers |
| C) | zero. |
| D) | infinity instantaneously. |
93. Which of the following statements associated with the magnetic field is correct?
| A) | The electric current produces magnetic field only in presence of a coil. |
| B) | The electric current always produces a magnetic field. |
| C) | Only large currents produce a magnetic field. |
| D) | The electric current produces magnetic field only in presence of an iron core |
94. Core of an electromagnet should have
| A) | none of these answers |
| B) | low coercivity. |
| C) | both low coercivity and high susceptibility. |
| D) | high susceptibility. |
95. Unit for the quantity of electricity is
| A) | ampere-hour |
| B) | joule |
| C) | coulomb |
| D) | watt |
96. Which of the following is the unit of magnetic flux density?
| A) | lumens |
| B) | tesla |
| C) | weber |
| D) | none of these answers |
97. The relative permeability of a ferromagnetic material is
| A) | more than 10 |
| B) | more than 100 or 1000 |
| C) | less than one |
| D) | more than one |
98. The magnetic materials exhibit the property of magnetization because of
| A) | spin of nucleus |
| B) | all of these answers |
| C) | none of these answers |
| D) | spin of electrons |
| E) | orbital motion of electrons |
99. The two conductors of a transmission line carry equal current I in opposite directions. The force on each conductor is
| A) | proportional to distance between the conductors |
| B) | proportional to I |
| C) | proportional to I2 |
| D) | inversely proportional to I2 |
100. What will be the magnetic potential difference across the air gap of 2 cm length in the magnetic field of 200 AT/m?
| A) | 4 AT |
| B) | 6 AT |
| C) | 10 AT |
| D) | 2 AT |
101. Soft magnetic material is
| A) | tungsten steel. |
| B) | iron. |
| C) | bismuth. |
| D) | Alcomax. |
102. Linkage flux per unit current is called
| A) | inductance. |
| B) | capacitance. |
| C) | resistance. |
| D) | capacitive reactance. |
103. A coil of 1,000 turns is wound on a core. A current of 1 A flowing through the coil creates a core flux 1 m Wb. The energy stored in the magnetic field is
| A) | 2 J. |
| B) | 0.25 J. |
| C) | 1 J. |
| D) | 0.5 J. |
104. The energy stored in the magnetic field of a solenoid 30 cm long and 3 cm diameter wound with 1,000 turns of wire carrying a current of 10 A is
| A) | 0.5 J |
| B) | 0.015 J |
| C) | 0.15 J |
| D) | 1.15 J |
105. The____ materials are a bit inferior conductors of magnetic flux than air
| A) | diamagnetic |
| B) | ferromagnetic |
| C) | paramagnetic |
| D) | dielectric |
106. Air gap has____ reluctance as compared to iron or steel path
| A) | lower |
| B) | higher |
| C) | little |
| D) | zero |
107. If in an iron cored coil the iron core is removed so as to make the air-cored coil, the inductance of the coil will be
| A) | none of these answers |
| B) | more. |
| C) | less. |
| D) | the same |
108. The emf induced in a coil due to the relative motion of a magnet is independent of
| A) | coil resistance. |
| B) | magnet motion. |
| C) | pole strength of the magnet. |
| D) | number of coil turns. |
109. Two identical coils of negligible resistance, when connected in series across a 50Hz fixed voltage source, draw a current of 10 A. When the terminals of one of the coils are reversed, the current drawn is 8 A. The coefficient of coupling between the two coils is
| A) | 8/10 |
| B) | 1/100 |
| C) | 1/9 |
| D) | 4/10 |
110. The attraction capacity of the electromagnet will increase if the
| A) | flux density decreases |
| B) | core length increases |
| C) | core area increases |
| D) | flux density increases |
111. The overall inductance of two coils connected in series, with mutual inductance aiding self-inductance is L1 with mutual inductance opposing self-inductance the overall inductance is L2. The mutual inductance M is given by
| A) | L1 – L2 |
| B) | L1 + L2 |
| C) | 1/4 (L1 – L2) |
| D) | 1/2 (L1 + L2) |
112. The change of the cross-sectional area of a conductor in a magnetic field will affect
| A) | resistance of conductor |
| B) | none of these answers |
| C) | reluctance of conductor and resistance of conductor |
| D) | reluctance of conductor |
113. A 200 turn coil having an axial length of 30 mm and a radius of 10 mm is pivoted in a magnetic field having a flux density of 0.8 T. If the coil carries a current of 0.5 A, the torque acting on the coil will be
| A) | 0.0048 N-m |
| B) | 0.048 N-m |
| C) | 4.8 N-m |
| D) | 0.48 N-m |
114. The stray line of magnetic flux is defined as
| A) | a line vertical to the flux lines |
| B) | a line of magnetic flux in a non-uniform field |
| C) | a line of magnetic flux which does not follow the designed path |
| D) | the mean length of a ring shaped coil |
115. Magnetic flux density emerging out of a closed surface is
| A) | zero. |
| B) | none of these answers |
| C) | infinite. |
| D) | dependent upon the magnetic movement inside the closed surface. |
116. Susceptibility is positive for
| A) | ferromagnetic substances |
| B) | non-magnetic substances |
| C) | diamagnetic substances |
| D) | none of these answers |
117. Two conducting thin coils X and Y (identical except for a thin cut in coil Y) are placed in a uniform magnetic field which is decreasing at a constant rate. If the plane of the coils is perpendicular to the field lines, which of the following statement is correct? As a result, emf is inducted in
| A) | coil Y only. |
| B) | coil X only. |
| C) | both the coils. |
| D) | none of the two coils |
118. When a single turn coil rotates in a uniform magnetic field, at a uniform speed the induced emf will be
| A) | alternating. |
| B) | steady. |
| C) | none of these answers |
| D) | pulsating. |
119. The relative permeability of____materials is not constant
| A) | ferromagnetic |
| B) | diamagnetic |
| C) | insulating |
| D) | paramagnetic |
120. Permanent magnets are normally made of
| A) | alnico alloys |
| B) | aluminium |
| C) | cast iron |
| D) | wrought iron |
121. Inductance has the dimensions of
| A) | none of these answers |
| B) | flux/current. |
| C) | ( voltage |
| D) | flux/length. |
122. The retentivity (a property) of material is useful for the construction of
| A) | permanent magnets |
| B) | non-magnetic substances |
| C) | transformers |
| D) | electromagnets |
123. An air gap is usually inserted in magnetic circuits to
| A) | none of these answers |
| B) | increase m.m.f. |
| C) | prevent saturation |
| D) | increase the flux |
124. An infinitely long straight conductor located along Z-axis carries a current I in the +ve Z-direction. The magnetic field at any point P in the X-Y plane is in which direction?
| A) | In the positive Z-direction. |
| B) | In the negative Z-direction |
| C) | In the direction perpendicular to the radial line OP (in X-Y plane) joining the origin O to the point P. |
| D) | Along the radial line OP. |
125. The magneto-motive force is
| A) | the flow of an electric current |
| B) | the sum of all currents embraced by one line of magnetic field |
| C) | the passage of magnetic field through an exciting coil |
| D) | the voltage across the two ends of exciting coil |
126. The field at any point on the axis of a current-carrying coil will be
| A) | zero. |
| B) | at an angle of 45° with the axis. |
| C) | perpendicular to the axis. |
| D) | parallel to the axis. |
127. A rectangular magnet of magnetic moment M is cut into two piece of the same length, the magnetic moment of each piece will be
| A) | M |
| B) | M/2 |
| C) | 2 M |
| D) | M/4 |
128. The coils having self-inductance of 10 mH and 15 mH and an effective inductance of 40 mH, when connected in series aiding. What will be the equivalent inductance if we connect them in series opposing?
| A) | 20 mH |
| B) | 5 mH |
| C) | zero |
| D) | 10 mH |
129. Main causes of noisy solenoid are
| A) | uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts |
| B) | strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force |
| C) | none of these answers |
| D) | strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force & uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts |
130. A permeable substance is one
| A) | which is a strong magnet |
| B) | through which the magnetic lines of force can pass very easily. |
| C) | which is a bad conductor |
| D) | none of these answers |
131. Ferrites are____ materials
| A) | none of these answers |
| B) | diamagnetic |
| C) | ferromagnetic |
| D) | paramagnetic |
132. Which of the following is expected to have the maximum permeability?
| A) | Ebonite |
| B) | Brass |
| C) | Zinc |
| D) | Copper |
133. Image theory is applicable to problems involving
| A) | neither electrostatic nor magnetostatic field. |
| B) | magnetostatic field only. |
| C) | both electrostatic and magnetostatic fields. |
| D) | the electrostatic field only. |
134. A material for good magnetic memory should have
| A) | low hysteresis loss |
| B) | high permeability |
| C) | low retentivity |
| D) | high retentivity |
135. When two ends of a circular uniform wire are joined to the terminals of a battery, the field at the center of the circle
| A) | will be infinite |
| B) | will be zero |
| C) | will depend on the radius of the circle |
| D) | will depend on the amount of e.m.f. applied |
136. Which of the following statements holds of the divergence of electric and magnetic flux densities?
| A) | It is zero for the magnetic flux density. |
| B) | These are zero for static densities but non-zero for time varying densities |
| C) | It is zero for the electric flux density. |
| D) | Both are zero. |
137. Soft magnetic materials have
| A) | high residual magnetism. |
| B) | low resistivity. |
| C) | high permeability and low coercive force. |
| D) | low permeability and high coercive force. |
138. When a magnet is in motion relative to a coil the induced e.m.f. does not depend upon
| A) | resistance of the coil |
| B) | motion of the magnet |
| C) | number of turns of the coil |
| D) | pole strength of the magnet |
139. If the two conductors carry current in opposite directions there will be
| A) | no force between them. |
| B) | a force of attraction between the two conductors. |
| C) | none of these answers |
| D) | a force of repulsion between the two conductors |
140. When a piece of iron is placed in a magnetic field
| A) | the magnetic lines of force will bend away from their usual paths in order to go away from the piece. |
| B) | there will be no effect on the magnetic field. |
| C) | the magnetic lines of force will bend away from their usual paths so as to pass through the piece. |
| D) | none of these answers |
141. A ferromagnetic core subjected to cycles of magnetisation will exhibit hysteresis when the cycle is
| A) | alternating |
| B) | any of these answers |
| C) | pulsating |
| D) | rotating |
142. Mutual inductance between two magnetically coupled coils depends on the
| A) | permeability of the core material. |
| B) | number of turns of the coils. |
| C) | all of these answers |
| D) | the cross-sectional area of their common core. |
143. The working of a meter is based on the use of a permanent magnet. In order to protect the meter functioning from stray magnetic fields
| A) | a shielding of a non-magnetic material is used |
| B) | a soft iron shielding is used |
| C) | a plastic shielding is provided |
| D) | meter is surrounded by strong magnetic fields |
144. The inductance of a long solenoid of length 1,000 mm wound uniformly with 3000 turns on a cylindrical paper tube of 60 mm diameter is
| A) | 3.2 H |
| B) | 3.2 μH |
| C) | 3.2 mH |
| D) | 32 mH |
145. The susceptibility of paramagnetic materials generally lies between
| A) | 10-3 and 10-5 |
| B) | 10-3 and 10-7 |
| C) | 10-4 and 10-8 |
| D) | 10-2 and 10-5 |
146. The left hand rule correlates to
| A) | magnetic field, electric field and direction of force on a conductor |
| B) | current, induced e.m.f. and direction of force on a conductor |
| C) | self induction, mutual induction and direction of force on a conductor |
| D) | current, magnetic field and direction of force on a conductor |
147. Lower the self inductance of a coil
| A) | more will be the emf induced. |
| B) | smaller the delay in establishing steady current through it. |
| C) | lesser the flux produced by it. |
| D) | more will be the weber-toms. |
148. The force experienced by a current carrying conductor lying parallel to a magnetic field is
| A) | B Il. |
| B) | B Il cos θ |
| C) | zero. |
| D) | B Il sin θ |
149. The inductance of a single layer solenoid of 10 turns is 5 μH. Which one cf the following is the correct value of inductance when the number of turns is 20 and the length is doubled?
| A) | 5 μH |
| B) | 40 μH |
| C) | 20 μH |
| D) | 10 μH |
150. A material which is slightly repelled by a magnetic field is known as
| A) | diamagnetic material |
| B) | paramagnetic material |
| C) | ferromagnetic material |
| D) | conducting material |
151. Which of the following statement(s) is/are correct?
1. Ferromagnetic substances have very large negative values of susceptibility.
2. Diamagnetic substances have very small negative values of suceptibility.
3. Paramagnetic substances have very small positive values of susceptibility.
4. The permeability of diamagnetic substances is slightly greater than unity.
| A) | 1 and 4. |
| B) | 2 and 3. |
| C) | 4 alone. |
| D) | 3 and 4. |
152. The magnetic field intensity (in A/m) at the centre of a circular coil of diameter 1 m and carrying a current of 2 A is
| A) | 3 |
| B) | 2 |
| C) | 8 |
| D) | 4 |
153. Aluminium and platinum are____materials.
| A) | paramagnetic |
| B) | diamagnetic |
| C) | ferromagnetic |
| D) | insulating |
154. The property of a material which opposes the creation of magnetic flux in it is known as
| A) | reluctance |
| B) | magnetomotive force |
| C) | reluctivity |
| D) | permeance |
155. A keeper is used for
| A) | restoring of lost flux. |
| B) | providing a closed path for the magnetic flux. |
| C) | changing the direction of magnetic lines of force. |
| D) | amplification of flux. |
156. One maxwell is equal to
| A) | 10-8 webers |
| B) | 104 webers |
| C) | 10-4 webers |
| D) | 108 webers |
157. The electromagnet has 50 turns and a current of 1 A flows through the coil. If the length of the magnet circuit is 200 mm, what is the magnetic field strength ?
| A) | 2500 AT/m |
| B) | 2.5 AT/m |
| C) | 250 AT/m |
| D) | 25 AT/m |
158. Which of the following inductors will have the least eddy current losses?
| A) | laminated iron cored. |
| B) | iron cored. |
| C) | wooden cored |
| D) | air-cored. |
159. Paramagnetic materials have a relative permeability
| A) | slightly more than unity |
| B) | equal to that ferromagnetic materials |
| C) | slightly less than unity |
| D) | equal to unity |
160. Hard steel is suitable for making permanent magnets because
| A) | its hysteresis loop has large area |
| B) | its mechanical strength is high |
| C) | it has good residual magnetism |
| D) | its mechanical strength is low |
161. Those materials are well suited for making permanent magnets which have____ retentivity and____ coercivity
| A) | low, low |
| B) | high, high |
| C) | low, high |
| D) | high, low |
162. In case all the flux from the current in coil 1 links with coil 2, the coefficient of coupling will be
| A) | 1.0 |
| B) | 0.5 |
| C) | zero |
| D) | 2.0 |
163. Materials subjected to rapid reversal of magnetism should have
| A) | high coercivity and low density |
| B) | large area of B-H loop |
| C) | high coercivity and high retentivity |
| D) | high permeability and low hysteresis loss |
164. The force between two long parallel conductors is inversely proportional to
| A) | current in one conductor |
| B) | distance between the conductors |
| C) | product of current in two conductors |
| D) | radius of conductors |
165. A keeper is used to
| A) | restore lost flux |
| B) | provide a closed path for flux |
| C) | change the direction of magnetic lines |
| D) | amplify flux |
166. Strength of an electromagnet can be increased by
| A) | increasing the cross-sectional area |
| B) | increasing current supply |
| C) | increasing the number of turns |
| D) | all of these answers |
167. Iron loss is known as
| A) | hysteresis loss. |
| B) | eddy current loss. |
| C) | none of these answers |
| D) | hysteresis loss and eddy current loss |
168. The ratio of intensity of magnetization to the magnetisation force is known as
| A) | susceptibility |
| B) | none of these answers |
| C) | flux density |
| D) | relative perimeability |
169. The area of hysteresis loss is a measure of
| A) | permeance |
| B) | magnetic flux |
| C) | energy loss per cycle |
| D) | permittivity |
170. Hysteresis loop in case of magnetically hard materials is more____ in shape as compared to magnetically soft materials.
| A) | rectangular |
| B) | circular |
| C) | triangular |
| D) | none of these answers |
171. The relative permeability is less than unity is case of
| A) | ferrites |
| B) | diamagnetic materials |
| C) | ferromagnetic materials |
| D) | non-ferrous materials |
172. What will be the current passing through the ring shaped air cored coil when number of turns is 800 and ampere turns are 3200?
| A) | 6 |
| B) | 4 |
| C) | 2 |
| D) | 8 |
173. One tesla is equal to
| A) | 1 Wb/mm2 |
| B) | 1 Wb/m |
| C) | 1 Wb/m2 |
| D) | 1 mWb/m2 |
174. Magnetism of a magnet can be destroyed by
| A) | hammering |
| B) | by inductive action of another magnet |
| C) | heating |
| D) | all of these answers |
175. The coercive force in a ferromagnetic material is related to the
| A) | area enclosed by the B-H loop. |
| B) | maximum value of B on the B-H loop. |
| C) | intercept on the negative H axis of the B-H loop. |
| D) | intercept on the positive B axis of the B-H loop. |
176. The unit(s) of inductance is/are
| A) | Henry. |
| B) | all of these answers |
| C) | volt-second/A. |
| D) | Wb/A. |
177. Magnetising steel is normals difficult because
| A) | it has low permeability |
| B) | it lias high permeability |
| C) | it corrodes easily |
| D) | it has high specific gravity |
178. Indicate which of the following material does not retain magnetism permanently.
| A) | Hardened steel |
| B) | None of these answers |
| C) | Soft iron |
| D) | Stainless steel |
179. In all cases of electromagnetic induction, an induced voltage will cause a current to flow in a closed circuit in such a direction that the magnetic field which is caused by that current will oppose the change that produces the current, is the original statement of
| A) | Fleming’s law of induction. |
| B) | Faraday’s law of magnetic induction. |
| C) | Lenz’s law |
| D) | Ampere’s law. |
180. The magnetic field required to reduce the residual magnetisation to zero is called
| A) | hysteresis. |
| B) | retentivity. |
| C) | saturation magnetisation |
| D) | coercivity. |
181. Substances winch have permeability less than the permeability of free space are known as
| A) | paramagnetic |
| B) | ferromagnetic |
| C) | bipolar |
| D) | diamagnetic |
182. Which part of the magnetic path requires largest m.m.f ?
| A) | Core |
| B) | Inductance |
| C) | Air gap |
| D) | Coil |
183. The magnetisation and applied field in ferromagnetic materials are related
| A) | sinusoidally |
| B) | linearly |
| C) | parabolically |
| D) | non-linearly |
184. An open coil has
| A) | infinite resistance and zero inductance. |
| B) | infinite resistance and infinite inductance. |
| C) | zero resistance and infinite inductance |
| D) | zero resistance and zero inductance. |
185. The unit of reluctance is
| A) | 1/henry |
| B) | metre/henry |
| C) | henry/metre |
| D) | henry |
186. Reciprocal of permeability is
| A) | susceptibility |
| B) | permittivity |
| C) | reluctivity |
| D) | conductance |
187. In order to minimise loss due to hysteresis the magnetic material should have
| A) | high hysteresis coefficient |
| B) | small B-H loop area. |
| C) | high retentivity |
| D) | large coercive force. |
| E) | high resistivity |
188. A straight conductor of circular x-section carries a current. Which one of the following statements is true in this regard?
| A) | A radial force acts away from the axis tending to increase its cross-section. |
| B) | No force acts on the conductor at any point |
| C) | A radial force acts towards the axis tending to reduce its cross-section. |
| D) | An axial force acts on the conductor tending to increase its length. |
189. If a current carrying conductor is placed in a magnetic field, the mechanical force experienced on the conductor is determined by
| A) | any of these answers |
| B) | simple product. |
| C) | dot product. |
| D) | cross product. |
190. The materials having low retentivity are suitable for making
| A) | none of these answers |
| B) | permanent magnets |
| C) | weak magnets |
| D) | temporary magnets |
191. Consider the following statements:
The force per unit length between two stationary parallel wires carrying (steady) currents
1. is inversely proportional to the separation of wires.
2. is proportional to the magnitude of each current.
3. satisfies Newton’s third law.
| A) | 2 and 3 are correct |
| B) | 1 and 3 are correct |
| C) | 1, 2 and 3 are correct. |
| D) | 1 and 2 are correct |
192. A magnetic field exists around
| A) | moving charges |
| B) | aluminium |
| C) | iron |
| D) | copper |
193. ∇B is based on
| A) | continuity equation. |
| B) | Ampere’s law. |
| C) | Lenz’s law. |
| D) | Gauss’s law. |
194. Which of the following statements is correct?
| A) | The magnetic flux inside an exciting coil is zero |
| B) | The magnetic flux inside the exciting coil is greater than its outside surface |
| C) | The magnetic flux inside an exciting coil is lower than its outside surface |
| D) | The magnetic flux inside the exciting coil is same as on its outside surface |
195. In order to minimise loss due to hysteresis, the magnetic material should have
| A) | high resistivity |
| B) | high retentivity |
| C) | large B-H loop area |
| D) | low hysteresis co-efficient |
196. The Biot-savart’s law is a general modification of
| A) | Kirchhoffs law |
| B) | Faraday’s laws |
| C) | Lenz’s law |
| D) | Ampere’s law |
197. A magnetic circuit requires 800 AT to produce a certain quantity of flux in magnetic circuit.
If its excitation coil has 100 turns and 5 ω resistance, the voltage to be applied in exciting coil is
| A) | 8 V |
| B) | 40 V |
| C) | 60 V |
| D) | 80 V |
198. Hysteresis loss least depends on
| A) | steinmetz co-efficient of material |
| B) | ambient temperature |
| C) | volume of material |
| D) | frequency |
199. Magnetic current is composed of which of the following?
| A) | Both conduction and displacement components. |
| B) | Only displacement component. |
| C) | Neither conduction component nor displacement component. |
| D) | Only conduction component. |
200. Gilbert is a unit of
| A) | magnetomotive force |
| B) | conductance |
| C) | permittivity |
| D) | electromotive force |
201. Materials subjected to rapid reversals of magnetism should have
| A) | large coercivity and high retentivity. |
| B) | low permeability and large coercivity |
| C) | large B-H loop area. |
| D) | high permeability and low hysteresis loss. |
202. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is____ A/s
| A) | 0.05 |
| B) | 50 |
| C) | 500 |
| D) | 20 |
203. Relative permeability of vacuum is
| A) | 1 |
| B) | 1 H/m |
| C) | 1/4 π |
| D) | 4π x 10-7 H/m |
204. Which of the following statements is correct?
| A) | The conductivity of ferrites is same as that of ferromagnetic materials |
| B) | The conductivity of ferrites is very high |
| C) | The conductivity of ferromagnetic materials is better than ferrites |
| D) | The conductivity of ferrites is better than ferromagnetic materials |
205. Permeability in a magnetic circuit corresponds to____ in an electric circuit.
| A) | resistance |
| B) | conductance |
| C) | conductivity |
| D) | resistivity |
206. Fleming’s left hand rule is used to find
| A) | direction of magnetic field due to current carrying conductor |
| B) | direction of force on a current carrying conductor in a magnetic field |
| C) | polarity of a magnetic pole |
| D) | direction of flux in a solenoid |
207. The area of hysteresis loop is a measure of
| A) | permeance. |
| B) | mmf per cycle |
| C) | energy loss per cycle |
| D) | magnetic flux |
208. The bar magnet has
| A) | none of these answers |
| B) | the dipole moment and monopole moment |
| C) | the dipole moment |
| D) | monopole moment |
209. In the left hand rule, forefinger always represents
| A) | magnetic field |
| B) | current |
| C) | direction of force on the conductor |
| D) | voltage |
210. The mutual inductance between two coupled coils is 10 mH.
If the turns in one coil are doubled and that in the other are halved, then the mutual inductance will be
| A) | 5 mH |
| B) | 10 mH |
| C) | 20 mH |
| D) | 14 mH |
211. Temporary magnets are used in
| A) | loud-speakers |
| B) | motors |
| C) | all of these answers |
| D) | generators |
212. The transformer cores operating at microwave frequency range, are usually made of
| A) | copper |
| B) | silicon steels |
| C) | ferrites |
| D) | carbon |
213. Which of the following statements associated with inductors is wrong?
| A) | A finite amount of energy can be stored in an inductor even if voltage across it is zero, such as when the current through it is constant. |
| B) | An inductor is a sort of open circuit to dc. |
| C) | An inductor is a sort of short circuit to dc. |
| D) | An inductor never dissipates energy but only stores it. |
214. Point out the wrong statement.
Magnetic leakage is undesirable in electric machines because it
| A) | increases their cost of manufacture |
| B) | produces fringing |
| C) | leads to their increased weight |
| D) | lowers their power efficiency |
215. If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity
| A) | less than that of disc but in opposite direction |
| B) | equal to that of disc and in the same direction |
| C) | less than that of disc and in the same direction |
| D) | equal to that of disc and in the opposite direction |
216. An electromagnetic field is radiated from
| A) | an oscillating dipole |
| B) | a conductor carrying ade current. |
| C) | a stationary point charge. |
| D) | a capacitor with ade voltage. |
217. Which of the following is a vector quantity?
| A) | Magnetic potential |
| B) | Magnetic field intensity. |
| C) | Magnetic flux density. |
| D) | Susceptibility. |
218. The laws of electromagnetic induction (Faraday’s md Lenz’s laws) are summarized in the following equation:
| A) | e = LR |
| B) | e = L (di/dt) |
| C) | e = – φ / dt |
| D) | none of these answers |
219. Silicon steel is used in electrical machines because it has
| A) | low hysteresis loss |
| B) | low coercivity |
| C) | low retentivity |
| D) | high coercivity |
220. When an iron piece is placed in a magnetic field
| A) | the iron piece will break |
| B) | the magnetic lines of force will bend away from their usual paths in order to go away from the piece |
| C) | the magnetic lines of force will bend away from their usual paths in order to pass through the piece |
| D) | the magnetic field will not be affected |
221. At a certain current, the energy stored in an iron-cored coil is 1,000 J and its copper loss is 2,000W. The time constant (in seconds) of the coil is
| A) | 1.0 |
| B) | 0.5 |
| C) | 2.0 |
| D) | 0.25 |
222. There is a constant homogeneous magnetic field pointing in a vertical direction. A metallic wire in the form of a square is rotated about a horizontal axis passing through the middle points of its opposite arms. The emf generated in the square is
| A) | oscillatory. |
| B) | varying with time t as t2 |
| C) | finite and constant. |
| D) | zero. |
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