Explore topic-wise MCQs in Electromagnetic Theory.

This section includes 120 Mcqs, each offering curated multiple-choice questions to sharpen your Electromagnetic Theory knowledge and support exam preparation. Choose a topic below to get started.

51.

Ampere’s law for current element is the other name for.

A. Biot-Savart law
B. Coulomb’s law
C. Divergence theorem
D. Curl
Answer» B. Coulomb’s law
52.

Given is the magnetic field intensity \(\bar H = 3{\bar a_x} + 7y{\bar a_y} + 2x{\bar a_z}\;A/m\). Calculate the current density J̅ (A/m2).

A. 3a̅x
B. -2a̅y
C. 12a̅y
D. -7a̅z
Answer» C. 12a̅y
53.

Calculate the reluctance of a magnetic coil which is wounded uniformly on an iron core provided that the relative permeability of the iron is 1400. Also, the length of the magnetic circuit is 70 cm and the cross-sectional area of the core is 5 cm2.

A. 3.6 × 105 AT/Wb
B. 7.9 × 105 AT/Wb
C. 7.9 × 108 AT/Wb
D. 4.6 × 108 AT/Wb
Answer» C. 7.9 × 108 AT/Wb
54.

For the figure shown below, the permeability in the core is 4 × 10-4 Wb/A-turns-m. What is the value of flux density (in T) in the core?

A. 0.2
B. 0.382
C. 0.6
D. 1
Answer» C. 0.6
55.

Directions: The following item consists of two statements, one labeled as the 'Statement (I)' and the other as 'Statement (II)'. Examine these two statements carefully and select the answers to these items using the codes given below:Statement (I): A cylindrical conductor of radius R carries a current I. The magnetic field intensity within the conductor increases linearly with the radial distance r < R.Statement (II): The current enclosed increases as the square of the radial distance while the circumference increases linearly with the radial distance.Codes:

A. Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)
B. Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I)
C. Statement (I) is true but Statement (II) is false
D. Statement (I) is false but Statement (II) is true
Answer» B. Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I)
56.

A self-induced voltage of a current-carrying coil which is wound on an iron core having 1 A current is independent of ________.

A. Number of turns of the coil
B. Variation in current
C. Variation in voltage to the coil
D. The resistance of the magnetic path
Answer» D. The resistance of the magnetic path
57.

In a magnetic circuit, which of the following is similar to current and resistance in an electric circuit?

A. Magnetomotive force and reluctance
B. Flux and reluctance
C. Reluctance and flux density
D. Reluctivity and resistivity
Answer» C. Reluctance and flux density
58.

Following materials are givenA) NickelB) Silicon iron C) SilverD) CobaltArrange them in ascending order of relative permeabilityChoose the correct answer from the options given below:

A. C, D, B, A
B. C, D, A, B
C. B, D, A, C
D. C, A, D, B
Answer» C. B, D, A, C
59.

A 0.5 meter long conductor carrying a current of 2 amperes is placed in a magnetic field having the flux density 0.05 Wb/m2. What will be the amount of force experienced by the conductor?

A. 1 Nw
B. 2 Nw
C. 0.05 Nw
D. 0.5 Nw
Answer» D. 0.5 Nw
60.

Oxygen is a/an ____ gas.

A. inert
B. ferromagnetic
C. paramagnetic
D. diamagnetic
Answer» D. diamagnetic
61.

If the current density inside a straight conductor is uniform over its cross-section, the flux density variation inside the conductor at different distances from its centre is

A. linear
B. square of the distance
C. inverse of the distance
D. exponential
Answer» B. square of the distance
62.

A steady current I is flowing in the –x direction through each of two infinitely long wires at \(y = \pm \frac{L}{2}\) as shown in the figure. The permeability of the medium is \({\mu _0}\). The \(\vec B\) – field at (0, L, 0) is

A. \(- \frac{{4{\mu _0}I}}{{3\pi L}}\hat z\)
B. \(+ \frac{{4{\mu _0}I}}{{3\pi L}}\hat z\)
C. 0
D. \(- \frac{{3{\mu _0}I}}{{4\pi L}}\hat z\)
Answer» B. \(+ \frac{{4{\mu _0}I}}{{3\pi L}}\hat z\)
63.

A cast steel electromagnet has an air gap length of 0.3 cm. Find the ampere-turns for the air gap to produce a flux density of 0.7 Wb/m2 in the air gap.

A. 2100 AT
B. 1671 AT
C. 1447 AT
D. 167 AT
Answer» C. 1447 AT
64.

A coil having area of 300 cm2 and 120 turns is removed from a 60 T magnetic field acting normally in 2 seconds. What is the magnitude of the induced EMF (in V) in the coil?

A. 108
B. 112
C. 104
D. 120
Answer» B. 112
65.

Materials that have a negative value of χ (susceptibility) of the order of 10-4 to 10-6 are called:

A. Ferromagnetic
B. Paramagnetic
C. Diamagnetic
D. Ferrimagnetic
Answer» D. Ferrimagnetic
66.

A coil of wire of 0.01 mm2 area of 1000 turns is wound on a core. It is subjected to w flux density of 100 mWb/mm2 by a 1 A current. The energy stored in the coil is

A. 2.0 J
B. 1.5 J
C. 1.0 J
D. 0.5 J
Answer» E.
67.

Determine the current through a coil (in A), if the coil has 140 turns and produces mmf of 14 Amp-turns.

A. 0.3
B. 0.4
C. 0.6
D. 0.1
Answer» E.
68.

Magnetic flux will be _________ if the surface area vector of a surface is perpendicular to the magnetic field.

A. Zero
B. Unity
C. Close to maximum
D. Maximum
Answer» B. Unity
69.

A coil having an inductance of 150 mH is carrying a current of 5 Amp. If the current is reduced to zero in 1 millisecond, the self-induced emf will be -

A. 125 V
B. 375 V
C. 500 V
D. 750 V
Answer» E.
70.

A conductor of length 100 cm moves right angles to a magnetic field of flux density of 2 wb/sq.m with the velocity of 25 m/second. The induced emf in the conductor will be

A. 25 volts
B. 50 volts
C. 75 volts
D. 10 volts
Answer» C. 75 volts
71.

Magnetic disk, electric motors, speakers, relays use which of the following elements?

A. Geothermal energy
B. Hydrochemical agents
C. Electromagnets
D. None of these
Answer» D. None of these
72.

If the area of cross-section is reduced to half of its original value, then what will happen to the flux density?

A. Doubled
B. Halved
C. Remain same
D. One-fourth
Answer» B. Halved
73.

How to estimate the self-induced EMF in a coil with L as self-inductance and carrying a current i(t)?

A. L × i(t)
B. L/i(t)
C. L × dt/di(t)
D. \(L \times \frac{{di\left( t \right)}}{{dt}}\)
Answer» E.
74.

In a material, using a magnetic field of 1.75 × 105 A/m, a magnetic flux density of 0.2182 Wb/m2 is produced. Calculate its permeability in (μH/m).

A. 0.6
B. 0.4
C. 1
D. 1.2
Answer» E.
75.

A long straight wire carries a current I = 10 A, the magnetic field intensity at a distance of 1.59 m is

A. 0.1 Am-1
B. 1 Am-1
C. 10 Am-1
D. 100 Am-1
Answer» C. 10 Am-1
76.

Eddy currents are the currents generated in

A. Moving conductor in the stationary magnetic field
B. Stationary conductor in changing magnetic Field
C. Both moving conductor in stationary magnetic field & stationary conductor in changing magnetic Field
D. None of these
Answer» D. None of these
77.

A series magnetic circuit will have _____.

A. total reluctance of a series circuit = difference of the reluctance in different part of the circuit
B. two or more paths for magnetic flux
C. different magnetic flux
D. same magnetic flux
Answer» E.
78.

Hysteresis loss can be reduced by

A. laminating the magnetic circuit
B. using material of narrow hysteresis loop
C. increasing m.m.f. of the circuit
D. None of these
Answer» C. increasing m.m.f. of the circuit
79.

Consider the following statements:A current I flows through a circular coil of one turn of radius R in the counter-clokcwise direction.1. The magnetic field at the centre is inversely proportional to R.2. The magnetic moment of the coil is directly proportional to R2.3. The magnetic field at its centre is directly proportional to R2.Which of the above statements is/are correct?

A. 1 and 2
B. 1 only
C. 2 and 3
D. 3 only
Answer» B. 1 only
80.

A conductor having a cross-sectional area a sq m carrying current \(I\vec j\;A\), lies in a magnetic field.\(\vec B = {B_0}\left( {\vec i + \vec j} \right)Wb/{m^2}\)The force density of the conductor isWhere, \(\vec i,\;\vec j\) and \(\vec k\) are orthogonal unit vectors.

A. \(\frac{{{B_0}}}{a}I\vec k\)
B. \( - \frac{{{B_0}}}{a} \cdot I\vec i\)
C. \(- \frac{{{B_0}}}{a}I\vec k\)
D. \(\frac{{{B_0}}}{a}I\vec j\)
Answer» D. \(\frac{{{B_0}}}{a}I\vec j\)
81.

magnet is able to attract ______.

A. Iron, aluminium, and brass
B. Iron, cobalt, and zinc
C. Iron, copper, and nickel
D. Nickel, cobalt, and steel
Answer» E.
82.

Faraday's Law is applicable

A. In all changing Magnetic fields
B. In all moving conductors
C. Only when the conductor is closed loop of thin wire
D. Only when magnetic field is of permanent magnet
Answer» D. Only when magnetic field is of permanent magnet
83.

In a straight wire, induced current depends upon which of the following factors?

A. The magnitude of magnetic flux density
B. Speed of movement of the wire
C. All of these
D. Length of wire
Answer» D. Length of wire
84.

Copper, Silver, Diamond are examples of:

A. Diamagnetic substance
B. Paramagnetic substances
C. Ferromagnetic substance
D. Ferrimagnetic substances
Answer» B. Paramagnetic substances
85.

Determine the value of magnetic field (in mT) at the centre of a 20 cm long solenoid, if the solenoid has 200 turns and carrying a current of 4 A.

A. 5
B. 8
C. 9
D. 11
Answer» B. 8
86.

A long straight non-magnetic conductor of radius 8 mm is carrying a uniform current density of 100 kA/m2 in the aZ direction. For this case, which one of the following is not correct?

A. ∇ × H = 105 aZ A/m2 for 0 < ρ < 8 mm
B. ∇ × B = 0
C. The magnetic field intensity for ρ > 8 mm is \(\frac{{{{10}^5}}}{2}\)ρaϕ A/m
D. The total current carried by the conductor is 6.4 π A
Answer» D. The total current carried by the conductor is 6.4 π A
87.

A conductor carries a current of 20A and is at right-angles to a magnetic field having a flux density of 0.9T. If the length of the conductor in the field is 30 cm, calculate the force acting on the conductor.

A. 2.6 N
B. 5.4 N
C. 54 N
D. 27 N
Answer» C. 54 N
88.

A solid iron cylinder is placed in a region containing a uniform magnetic field such that the cylinder axis is parallel to the magnetic field direction. The magnetic field lines inside the cylinder will

A. bend closer to the cylinder axis
B. bend farther away from the axis
C. remain uniform as before
D. cease to exist inside the cylinder
Answer» B. bend farther away from the axis
89.

Molybdenum is

A. Piezoelectric
B. Paramagnetic
C. Ferromagnetic
D. Ferrimagnetic
Answer» C. Ferromagnetic
90.

For the series magnetic circuit shown, find the flux density to develop magnetic flux of 4 × 10-4 Wb.

A. 8 × 10-7 T
B. 0.5 T
C. 0.02 T
D. 0.2 T
Answer» E.
91.

Consider the following statements relating to the electrostatic and magnetostatic fields:1. The relative distribution of charges on an isolated conducting body is dependent on the total charge of the body.2. The magnetic flux through any closed surface is zero.Which of the above statements is/are correct?

A. Neither 1 nor 2
B. 1 only
C. 2 only
D. Both 1 and 2
Answer» E.
92.

A car having an axle of 2 m length is travelling with 72 km/h at a vertical component of the earth’s magnetic field of 40 μWb/m2, the emf generated in the axle of a car will be

A. 1.2 mV
B. 1.6 mV
C. 2.2 mV
D. 2.6 mV
Answer» C. 2.2 mV
93.

How much eddy current loss does an air-core inductor have?

A. Very less
B. Constant
C. Zero
D. High
Answer» B. Constant
94.

A coil of 360 turns is linked by a flux of 200 μ Wb. If the flux is reversed in 0.01 second, then find the EMF induced in the coil.

A. 7.2 V
B. 0.72 V
C. 14.4 V
D. 144
Answer» D. 144
95.

On which of the following parameters the eddy current loss occurring in a material does not depend?

A. Magnetic flux Density
B. Frequency of variation of flux
C. Susceptibility
D. Volume of the material
Answer» D. Volume of the material
96.

Magnetic Bubbles are used as ______.

A. Routing telephone calls
B. Thermostat
C. Storage device
D. Strain gauge
Answer» D. Strain gauge
97.

Determine the value of current (in A) in a coil, if it has 60 numbers of turns and produces a mmf of 30 Amp-turns.

A. 0.8
B. 1.4
C. 1.2
D. 0.5
Answer» E.
98.

According to Faraday’s Law of electromagnetic induction, an emf is induced in a conductor whenever it

A. Lies in a magnetic field
B. Lies perpendicular to the magnetic field
C. Cut the magnetic field
D. Moves parallel to the direction of magnetic field
Answer» D. Moves parallel to the direction of magnetic field
99.

According to Ampere's law, the relationship between the force two parallel conductors, carrying a average voltage of the wave average voltage of the wave current of I1 and I2 and displaced with a distance of r for a section of length l, is given by:

A. F \(\propto \ \frac{I_1I_2L}{r^2}\)
B. F \(\propto \frac{I_1I_2L^2}{r}\)
C. F \(\propto \frac{I_1 I_2 L}{r}\)
D. F \(\propto \frac{I_1I_2}{r}\)
Answer» D. F \(\propto \frac{I_1I_2}{r}\)
100.

Determine the eddy current loss (in W) in a material having eddy current coefficient of 1, thickness of 0.03 m and volume of 2 cubic metre which is kept in a magnetic field of maximum flux density of 3 T and supplied by a frequency of 50 Hz.

A. 35.5
B. 30.5
C. 25.5
D. 40.5
Answer» E.