# Multiple choice question for engineering

## Set 1

1. The presence of parallel alignment of magnetic dipole moment is given by which materials?

a) Diamagnetic

b) Ferromagnetic

c) Paramagnetic

d) Ferromagnetic

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2. The magnetic materials follow which law?

a) Faraday’s law

b) Ampere law

c) Lenz law

d) Curie Weiss law

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3. Find the internal field when the applied field is 12 units, molecular field constant is 0.1 units and the magnetization is 74 units.

a) 86

b) 62

c) 752

d) 19.4

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4. In which materials the magnetic anisotropy is followed?

a) Diamagnetic

b) Paramagnetic

c) Ferromagnetic

d) Ferromagnetic

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5. Piezoelectric effect is analogous to which phenomenon?

a) Electrostriction

b) Magnetostriction

c) Anisotropy

d) Magnetization

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6. The converse of magnetostriction is called the

a) Magnetization

b) Magnetic anisotropy

c) Villari effect

d) Curie effect

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7. The materials having very small susceptibility at all temperatures are

a) Antiferromagnetic

b) Diamagnetic

c) Ferromagnetic

d) Paramagnetic

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8. Find the susceptibility when the curie constant is 0.2 and the difference in critical temperature and paramagnetic curie temperature is 0.01.

a) 2

b) 20

c) 0.02

d) 200

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9. The susceptibility is independent of temperature in which material?

a) Paramagnetic

b) Ferromagnetic

c) Diamagnetic

d) Ferromagnetic

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10. In ferromagnetic materials the susceptibility is infinity. State True/False

a) True

b) False

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## Set 2

1. The magnetic vector potential is a scalar quantity.

a) True

b) False

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2. Find the magnetic field intensity when the magnetic vector potential x i + 2y j + 3z k.

a) 6

b) -6

c) 0

d) 1

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3. The value of ∫ H.dL will be

a) J

b) I

c) B

d) H

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4. Given the vector potential is 16 – 12sin y j. Find the field intensity at the origin.

a) 28

b) 16

c) 12

d) 4

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5. Find the vector potential when the field intensity 60x^{2} varies from (0,0,0) to (1,0,0).

a) 120

b) -20

c) -180

d) 60

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^{2}dx = -20x

^{3}as x = 0->1 to get -20.

6. Find the flux density B when the potential is given by x i + y j + z k in air.

a) 12π x 10^{-7}

b) -12π x 10^{-7}

c) 6π x 10^{-7}

d) -6π x 10^{-7}

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^{-7}x (-3) = -12π x 10

^{-7}units.

7. The Laplacian of the magnetic vector potential will be

a) –μ J

b) – μ I

c) –μ B

d) –μ H

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^{2}(A) = -μ J, where μ is the permeability and J is the current density.

8. The magnetic vector potential for a line current will be inversely proportional to

a) dL

b) I

c) J

d) R

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9. The current element of the magnetic vector potential for a surface current will be

a) J dS

b) I dL

c) K dS

d) J dV

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10. The relation between flux density and vector potential is

a) B = Curl(A)

b) A = Curl(B)

c) B = Div(A)

d) A = Div(B)

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## Set 3

1. Find the Lorentz force due to a conductor of length 2m carrying a current of 1.5A and magnetic flux density of 12 units.

a) 24

b) 36

c) 32

d) 45

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2. Calculate the flux density due to a circular conductor of radius 100nm and current 5A in air.

a) 10

b) 100

c) 0.1

d) 1

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^{-9}, thus we get B = 4π x 10

^{-7}x 5/(2π x 100 x 10

^{-9}) = 10 units.

3. The torque expression of a current carrying conductor is

a) T = BIA cos θ

b) T = BA cos θ

c) T = BIA sin θ

d) T = BA sin θ

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4. Find the current in a dipole with a moment of 16 units and area of 9 units.

a) 1.78

b) 2.78

c) 1.87

d) 2.34

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5. The expression for magnetization is given by(I-current, A-area, V-volume)

a) M = IAV

b) M = IA/V

c) M = V/IA

d) M = 1/IAV

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6. Find the permeability of a medium whose susceptibility is 100.

a) -100

b) 99

c) -99

d) 101

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_{m}= μ

_{r}-1. To get permeability, μr = χm + 1 = 100 + 1 = 101 units.

7. Calculate the magnetization of a material with susceptibility of 50 and field intensity of 0.25 units.

a) 12.5

b) 25

c) 75

d) 37.5

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_{m}H. Put χm = 50 and H = 0.25, then M = 50 x 0.25 = 12.5 units.

8. Very small and positive susceptibility is found in

a) Ferromagnetic

b) Diamagnetic

c) Paramagnetic

d) Antiferromagnetic

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9. Which of the following materials is ferrimagnetic?

a) Fe

b) Sn

c) Fe_{2}O_{3}

d) FeCl

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_{2}O

_{3}is said to be a ferrimagnetic material.

10. Identify the diamagnetic material.

a) Silicon

b) Germanium

c) Silver

d) Cobalt

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## Set 4

1. The magnetostatics highly relies on which property?

a) Resistance

b) Capacitance

c) Inductance

d) Moment

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2. The inductance is the measure of

a) Electric charges stored by the material

b) Emf generated by energising the coil

c) Magnetic field stored by the material

d) Magnetization of dipoles

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3. Find the total flux in a coil of magnetic flux density 12 units and area 7 units.

a) 0.84

b) 0.96

c) 8.4

d) 9.6

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4. Find the energy of a coil of inductance 18mH and current passing through it 1.25A.(in 10^{-3} order)

a) 14.06

b) 61

c) 46.1

d) 28.12

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^{2}. Put L = 18 x 10

^{-3}and I = 1.25, thus we get E = 0.5 x 18 x 10

^{-3}x 1.25

^{2}= 14.06 x 10

^{-3}units.

5. Using Maxwell equation which of the following cannot be calculated directly?

a) B

b) D

c) A

d) H

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6. Which of the following relation will hold good?

a) D = μ H

b) B = ε E

c) E = ε D

d) B = μ H

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7. The permeability and permittivity of air or free space is unity. State true/false.

a) True

b) False

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8. Choose the best relation.

a) A = -Div(V)

b) V = Curl(A)

c) H = -Grad(V)

d) V = Div(E)

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9. Find the magnetic field when the magnetic vector potential is a unit vector.

a) 1

b) -1

c) 0

d) 2

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10. Find the force experienced by an electromagnetic wave in a conductor?

a) Electrostatic force

b) Magneto static force

c) Electro motive force

d) Lorentz force

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## Set 5

1. Find the induced EMF in an inductor of 2mH and the current rate is 2000 units.

a) 4

b) -4

c) 1

d) -1

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^{-3}and di/dt = 2000 in the equation. We get e = -2 x 10

^{-3}x 2000 = -4 units.

2. Find the work done in an inductor of 4H when a current 8A is passed through it?

a) 256

b) 128

c) 64

d) 512

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^{2}. On substituting L = 4 and I = 8, we get, W = 0.5 x 4 x 8

^{2}= 128 units.

3. Find the inductance of a material with 100 turns, area 12 units and current of 2A in air.

a) 0.75mH

b) 7.5mH

c) 75mH

d) 753mH

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^{2}A/I. On substituting N = 100, A = 0.12 and I = 2, we get L = 4π x 10

^{-7}x 100

^{2}x 0.12/2 = 0.75 units.

4. Calculate the magnetic energy when the magnetic intensity in air is given as 14.2 units(in 10^{-4} order)

a) 1.26

b) 2.61

c) 6.12

d) 1.62

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^{2}. Put H = 14.2 and in air μ = 4π x 10

^{-7}, we get E = 0.5 x 4π x 10

^{-7}x 14.2

^{2}= 1.26 x 10

^{-4}units.

5. Calculate the magnetic energy when the magnetic flux density is given by 32 units(in 10^{8} order)

a) 4.07

b) 7.4

c) 0.47

d) 7.04

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^{2}and we know that μH = B. On substituting we get a formula E = 0.5 B

^{2}/μ. Put B = 32 and in air μ = 4π x 10

^{-7}, we get E = 0.5 x 32

^{2}/4π x 10

^{-7}= 4.07 x 10

^{8}units.

6. Calculate the energy when the magnetic intensity and magnetic flux density are 15 and 65 respectively.

a) 755

b) 487.5

c) 922

d) 645

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^{2}= 0.5 BH, since B = μH. On substituting B = 65 and H = 15 we get E = 0.5 x 65 x 15 = 487.5 units.

7. Find the inductance when the energy is given by 2 units with a current of 16A.

a) 15.6mH

b) 16.5mH

c) 16.8mH

d) 15.8mH

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^{2}. To get L, put E = 2 and I = 16 and thus L = 2E/I

^{2}= 2 x 2/16

^{2}= 15.6mH.

8. Find the power of an inductor of 5H and current 4.5A after 2 seconds.

a) 25.31

b) 50.62

c) 102.4

d) 204.8

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^{2}. Thus, put L = 5 and I = 4.5 and we get E = 0.5 x 5 x 4.5

^{2}= 50.625 units To get power P = E/t = 50.625/2 = 25.31 units.

9. Find the turns in an solenoid of inductance 23.4mH , current 2A and area 15cm.

a) 900

b) 400

c) 498

d) 658

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^{2}A/I. Put L = 23.4 x 10

^{-3}, I = 2 and A = 0.15, we get N as 498 turns.

10. The energy of a coil depends on the turns. State True/False.

a) True

b) False