# Multiple choice question for engineering

## Set 1

1. Calculate the emf in a material with flux linkage of 3.5t^{2} at 2 seconds.

a) 3.5

b) -7

c) -14

d) 28

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^{2}, we get emf = -7t. At time t = 2sec, the emf will be -14 units.

2. Find the emf induced in a coil of 60 turns with a flux rate of 3 units.

a) -60

b) -180

c) 60

d) 180

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3. Find the electric field intensity of a charge 2.5C with a force of 3N.

a) -7.5

b) 7.5

c) 2.5/3

d) 3/2.5

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4. The electric field intensity of a field with velocity 10m/s and flux density of 2.8 units is

a) 0.28

b) 28

c) 280

d) 10/2.8

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5. The line integral of the electric field intensity is

a) Mmf

b) Emf

c) Electric potential

d) Magnetic potential

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6. Which of the following relations is correct?

a) MMF = ∫ B.dl

b) MMF = ∫ H.dl

c) EMF = ∫ E.dl

d) EMF = ∫ D.dl

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7. For static fields, the curl of E will be

a) Rotational

b) Irrotational

c) Solenoidal

d) Divergent

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8. The line integral of which parameter is zero for static fields?

a) E

b) H

c) D

d) B

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9. The magnitude of the conduction current density for a magnetic field intensity of a vector yi + zj + xk will be

a) 1.414

b) 1.732

c) -1.414

d) -1.732

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10. The charge density of a field with a position vector as electric flux density is given by

a) 0

b) 1

c) 2

d) 3

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## Set 2

1. The given equation satisfies the Laplace equation.

V = x^{2} + y^{2} – z^{2}. State True/False.

a) True

b) False

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^{2}(V) = 2+2-4 = 0. It satisfies the Laplacian equation. Thus the statement is true.

2. In free space, the Poisson equation becomes

a) Maxwell equation

b) Ampere equation

c) Laplace equation

d) Steady state equation

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^{2}(V) = -ρ/ε. In free space, the charges will be zero. Thus the equation becomes, Del

^{2}(V) = 0, which is the Laplace equation.

3. If Laplace equation satisfies, then which of the following statements will be true?

a) Potential will be zero

b) Current will be infinite

c) Resistance will be infinite

d) Voltage will be same

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4. Suppose the potential function is a step function. The equation that gets satisfied is

a) Laplace equation

b) Poisson equation

c) Maxwell equation

d) Ampere equation

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5. Calculate the charge density when a potential function x^{2} + y^{2} + z^{2} is in air(in 10-9 order)

a) 1/6π

b) 6/2π

c) 12/6π

d) 10/8π

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^{2}(V) = -ρ/ε. To find ρ, put ε = 8.854 x 10

^{-12}in air and Laplacian of the function is 2 + 2 + 2 = 6. Ρ = 6 x 10

^{-9}/36π = 1/6π units.

6. The function V = e^{x}sin y + z does not satisfy Laplace equation. State True/False.

a) True

b) False

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^{x}sin y i + e

^{x}cos y j + k. Div(Grad(V)) = e

^{x}sin y – e

^{x}sin y + 0= 0.Thus Laplacian equation Div(Grad(V)) = 0 is true.

7. Poisson equation can be derived from which of the following equations?

a) Point form of Gauss law

b) Integral form of Gauss law

c) Point form of Ampere law

d) Integral form of Ampere law

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^{2}(V)= -ρ/ε, which is the Poisson equation.

8. Find the charge density from the function of flux density given by 12x – 7z.

a) 19

b) -5

c) 5

d) -19

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9. Find the electric field of a potential function given by 20 log x + y at the point (1,1,0).

a) -20 i – j

b) -i -20 j

c) i + j

d) (i + j)/20

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10. When a material has zero permittivity, the maximum potential that it can possess is

a) ∞

b) -∞

c) Unity

d) Zero

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## Set 3

1. The best definition of polarisation is

a) Orientation of dipoles in random direction

b) Electric dipole moment per unit volume

c) Orientation of dipole moments

d) Change in polarity of every dipole

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2. Calculate the polarisation vector of the material which has 100 dipoles per unit volume in a volume of 2 units.

a) 200

b) 50

c) 400

d) 0.02

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3. Polarizability is defined as the

a) Product of dipole moment and electric field

b) Ratio of dipole moment to electric field

c) Ratio of electric field to dipole moment

d) Product of dielectric constant and dipole moment

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4. Calculate the energy stored per unit volume in a dielectric medium due to polarisation when P = 9 units and E = 8 units.

a) 1.77

b) 2.25

c) 36

d) 144

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5. Identify which type of polarisation depends on temperature.

a) Electronic

b) Ionic

c) Orientational

d) Interfacial

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6. Calculate the polarisation vector in air when the susceptibility is 5 and electric field is 12 units.

a) 3

b) 2

c) 60

d) 2.4

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7. In isotropic materials, which of the following quantities will be independent of the direction?

a) Permittivity

b) Permeability

c) Polarisation

d) Polarizability

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8. The total polarisation of a material is the

a) Product of all types of polarisation

b) Sum of all types of polarisation

c) Orientation directions of the dipoles

d) Total dipole moments in the material

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9. In the given types of polarisation, which type exists in the semiconductor?

a) Electronic

b) Ionic

c) Orientational

d) Interfacial or space charge

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10. Solids do not have which type of polarisation?

a) Ionic

b) Orientational

c) Interfacial

d) Electronic

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## Set 4

1. The power of the electromagnetic wave with electric and magnetic field intensities given by 12 and 15 respectively is

a) 180

b) 90

c) 45

d) 120

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2. The power of a wave of with voltage of 140V and a characteristic impedance of 50 ohm is

a) 1.96

b) 19.6

c) 196

d) 19600

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^{2}/2Zo, where V is the generator voltage and Zo is the characteristic impedance. on substituting the given data, we get P = 140

^{2}/(2×50) = 196 units.

3. The power reflected by a wave with incident power of 16 units is(Given that the reflection coefficient is 0.5)

a) 2

b) 8

c) 6

d) 4

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^{2}xPinc. On substituting the given data, we get Pref = 0.5

^{2}x 16 = 4 units.

4. The power transmitted by a wave with incident power of 16 units is(Given that the reflection coefficient is 0.5)

a) 12

b) 8

c) 16

d) 4

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^{2}) Pinc. On substituting the given data, we get Pref = (1- 0.5

^{2}) x 16 = 12 units. In other words, it is the remaining power after reflection.

5. The incident and the reflected voltage are given by 15 and 5 respectively. The transmission coefficient is

a) 1/3

b) 2/3

c) 1

d) 3

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6. The current reflection coefficient is given by -0.75. Find the voltage reflection coefficient.

a) -0.75

b) 0.25

c) -0.25

d) 0.75

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7. The attenuation is given by 20 units. Find the power loss in decibels.

a) 13.01

b) 26.02

c) 52.04

d) 104.08

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8. The reflection coefficient is 0.5. Find the return loss.

a) 12.12

b) -12.12

c) 6.02

d) -6.02

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9. The radiation resistance of an antenna having a power of 120 units and antenna current of 5A is

a) 4.8

b) 9.6

c) 3.6

d) 1.8

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^{2}Rrad, where Ia is the antenna current and Rrad is the radiation resistance. On substituting the given data, we get Rrad = Prad/Ia

^{2}= 120/5

^{2}= 4.8 ohm.

10. The transmission coefficient is given by 0.65. Find the return loss of the wave.

a) 9.11

b) 1.99

c) 1.19

d) 9.91

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11. The return loss is given as 12 decibel. Calculate the reflection coefficient.

a) 0.35

b) 0.55

c) 0.25

d) 0.75

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^{(-RL/20)}, by anti logarithm property. For the given return loss RL = 12, we get R = 10

^{(-12/20)}= 0.25.

12. Find the transmission coefficient of a wave, when the return loss is 6 decibel.

a) 0.498

b) 0.501

c) 0.35

d) 0.65

### View Answer

^{(-RL/20)}, by anti logarithm property. For the given return loss RL = 6, we get R = 10

^{(-6/20)}= 0.501. The transmission coefficient will be T = 1 – R = 1-0.501 = 0.498.

## Set 5

1. Calculate the capacitance of a material in air with area 20 units and distance between plates is 5m.

a) 35.36pF

b) 3.536pF

c) 35.36nF

d) 3.536nF

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^{-12}X 20/5 = 35.36pF.

2. The resistance of a material with conductivity 2millimho/m^{2}, length 10m and area 50m is

a) 500

b) 200

c) 100

d) 1000

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3. Find the inductance of a coil with permeability 3.5, turns 100 and length 2m. Assume the area to be thrice the length.

a) 131.94mH

b) 94.131mH

c) 131.94H

d) 94.131H

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^{2}A/l, where μ= μoμr is the permeability of air and the material respectively. N = 100 and Area = 3 X 2 = 6. L = 4π X 10

^{-7}X 100

^{2}X 6/2 = 131.94mH.

4. Find the current density of a material with resistivity 20 units and electric field intensity 2000 units.

a) 400

b) 300

c) 200

d) 100

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5. Find the current in a conductor with resistance 2 ohm, electric field 2 units and distance 100cm.

a) 1A

b) 10mA

c) 10A

d) 100mA

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6. In electric fields, D= ε E. The correct expression which is analogous in magnetic fields will be

a) H = μ B

b) B = μ H

c) A = μ B

d) H = μ A

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7. Find the force on a conductor of length 12m and magnetic flux density 20 units when a current of 0.5A is flowing through it.

a) 60

b) 120

c) 180

d) 200

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8. From the formula F = qE, can prove that work done is a product of force and displacement. State True/False

a) True

b) False

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9. Calculate the power of a material with electric field 100 units at a distance of 10cm with a current of 2A flowing through it.

a) 10

b) 20

c) 40

d) 80

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10. Compute the power consumed by a material with current density 15 units in an area of 100 units. The potential measured across the material is 20V.

a) 100kJ

b) 250kJ

c) 30kJ

d) 15kJ