# Multiple choice question for engineering

## Set 1

1. The charge within a conductor will be

a) 1

b) -1

c) 0

d) ∞

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2. For a conservative field which of the following equations holds good?

a) ∫ E.dl = 0

b) ∫ H.dl = 0

c) ∫ B.dl = 0

d) ∫ D.dl = 0

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3. Find the electric field if the surface density at the boundary of air is 10^{-9}.

a) 12π

b) 24π

c) 36π

d) 48π

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^{-9}and εo = 10

^{-9}/36π. We get E = 36π units.

4. Find the flux density at the boundary when the charge density is given by 24 units.

a) 12

b) 24

c) 48

d) 96

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5. Which component of the electric field intensity is always continuous at the boundary?

a) Tangential

b) Normal

c) Horizontal

d) Vertical

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6. The normal component of which quantity is always discontinuous at the boundary?

a) E

b) D

c) H

d) B

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7. The electric flux density of a surface with permittivity of 2 is given by 12 units. What the flux density of the surface in air?

a) 24

b) 6

c) 1/6

d) 0

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8. The electric field intensity of a surface with permittivity 3.5 is given by 18 units. What the field intensity of the surface in air?

a) 5.14

b) 0.194

c) 63

d) 29

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9. A wave incident on a surface at an angle 60 degree is having field intensity of 6 units. The reflected wave is at an angle of 30 degree. Find the field intensity after reflection.

a) 9.4

b) 8.4

c) 10.4

d) 7.4

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10. Find the permittivity of the surface when a wave incident at an angle 60 is reflected by the surface at 45 in air.

a) 1.41

b) 3.5

c) 2.2

d) 1.73

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## Set 2

1. Brewster angle is valid for which type of polarisation?

a) Perpendicular

b) Parallel

c) S polarised

d) P polarised

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2. The Brewster angle is expressed as

a) Tan^{-1}(n)

b) Tan^{-1}(n1/n2)

c) Tan^{-1}(n2/n1)

d) Tan (n)

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^{-1}(n2/n1).

3. The refractive index of a material with permittivity 16 is given by

a) 16

b) 256

c) 4

d) 8

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4. The reflection coefficient in the wave propagation when it is transmitted with the Brewster angle is

a) 0

b) 1

c) -1

d) Infinity

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5. The transmission coefficient of a wave propagating in the Brewster angle is

a) 0

b) 1

c) -1

d) Infinity

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6. A circularly polarised wave transmitted at the Brewster angle will be received as linearly polarised wave. State True/False

a) True

b) False

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7. An elliptically polarised wave transmitted at the Brewster angle will be received as an elliptically polarised wave. State True/False

a) True

b) False

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8. Find the Brewster angle of a wave transmitted from a medium of permittivity 4 to a medium of permittivity 2.

a) 35.26

b) 53.62

c) 26.35

d) 62.53

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^{-1}(n2/n1), where n = √ε. Thus we can express the formula in terms of permittivity as θb = tan

^{-1}√ (ε 2/ε 1). Here ε1 = 4 and ε2 = 2. Thus we get θb = tan

^{-1}√ (2/4) = tan

^{-1}(0.707) = 35.26 degree.

9. Find the ratio of refractive index of medium 2 to that of medium 1, when the Brewster angle is 60 degree.

a) 0.707

b) 1.5

c) 0.866

d) 1.732

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10. The Brewster angle is the angle of

a) Incidence

b) Reflection

c) Refraction

d) Transmission

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## Set 3

1. Standing waves occurs due to

a) Impedance match

b) Impedance mismatch

c) Reflection

d) Transmission

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2. Standing wave ratio is defined as the

a) Ratio of voltage maxima to voltage minima

b) Ratio of current maxima to current minima

c) Product of voltage maxima and voltage minima

d) Product of current maxima and current minima

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_{MAX}/V

_{MIN}.

3. Given that the reflection coefficient is 0.6. Find the SWR.

a) 2

b) 4

c) 6

d) 8

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4. The maxima and minima voltage of the standing wave are 6 and 2 respectively. The standing wave ratio is

a) 2

b) 3

c) 1/2

d) 4

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_{MAX}/V

_{MIN}. On substituting the given data, we get S = 6/2 = 3.

5. Find the standing wave ratio, when a load impedance of 250 ohm is connected to a 75 ohm line.

a) 0.3

b) 75

c) 250

d) 3.33

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6. Find the reflection coefficient of the wave with SWR of 3.5.

a) 0.55

b) 0.23

c) 0.48

d) 0.68

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7. The range of the standing wave ratio is

a) 0 < S < 1

b) -1 < S < 1

c) 1 < S < ∞

d) 0 < S < ∞

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8. For matched line, the standing wave ratio will be

a) 0

b) ∞

c) -1

d) 1

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9. The maximum impedance of a 50 ohm transmission line with SWR of 3 is

a) 50/3

b) 3/50

c) 150

d) 450

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_{max}= S Zo. On substituting for S = 3 and Zo = 50, we get Z

_{MAX}= 3 X 50 = 150 units.

10. The minimum impedance of a 75 ohm transmission line with a SWR of 2.5 is

a) 100

b) 50

c) 25

d) 30

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_{MIN}= Zo/S. Substituting the given data for S = 2.5 and Zo = 75, we get Z

_{min}= 75/2.5 = 30.

11. The standing wave ratio of short circuited and open circuited lines will be

a) 0

b) 1

c) -1

d) ∞

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12. The current reflection coefficient of a line with voltage reflection coefficient of 0.65 is given by

a) 0

b) 0.65

c) -0.65

d) 0.35

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## Set 4

1. Which of the following are conductors?

a) Ceramics

b) Plastics

c) Mercury

d) Rubber

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2. Find the range of band gap energy for conductors.

a) >6 eV

b) 0.2-0.4 eV

c) 0.4-2 eV

d) 2-6 eV

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3. Conduction in metals is due to

a) Electrons only

b) Electrons and holes

c) Holes only

d) Applied electric field

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4. Find the band gap energy when a light of wavelength 1240nm is incident on it.

a) 1eV

b) 2eV

c) 3eV

d) 4eV

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^{-6}/1240 x 10

^{-9}= 1eV.

5. Alternating current measured in a transmission line will be

a) Peak value

b) Average value

c) RMS value

d) Zero

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6. The current in a metal at any frequency is due to

a) Conduction current

b) Displacement current

c) Both conduction and displacement current

d) Neither conduction nor displacement current

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7. For conductors, the free electrons will exist at

a) Valence band

b) Middle of valence and conduction band

c) Will not exist

d) Conduction band

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8. The current flowing through an insulating medium is called

a) Conduction

b) Convection

c) Radiation

d) Susceptibility

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9. Find the conduction current density when conductivity of a material is 500 units and corresponding electric field is 2 units.

a) 500

b) 250

c) 1000

d) 2000

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10. Calculate the convection current when electron density of 200 units is travelling at a speed of 12m/s.

a) 16.67

b) 2400

c) 2880

d) 0.06

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## Set 5

1. Find the current when the charge is a time function given by q(t) = 3t + t^{2} at 2 seconds.

a) 3

b) 5

c) 7

d) 9

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2. The continuity equation is a combination of which of the two laws?

a) Ohm’s law and Gauss law

b) Ampere law and Gauss law

c) Ohm’s law and Ampere law

d) Maxwell law and Ampere law

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3. Calculate the charge density for the current density given 20sin x i + ycos z j at the origin.

a) 20t

b) 21t

c) 19t

d) -20t

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4. Compute the conductivity when the current density is 12 units and the electric field is 20 units. Also identify the nature of the material.

a) 1.67, dielectric

b) 1.67, conductor

c) 0.6, dielectric

d) 0.6, conductor

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5. Find the electron density when convection current density is 120 units and the velocity is 5m/s.

a) 12

b) 600

c) 24

d) 720

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6. Calculate the electric field when the conductivity is 20 units, electron density is 2.4 units and the velocity is 10m/s. Assume the conduction and convection current densities are same.

a) 2.4

b) 4.8

c) 3.6

d) 1.2

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7. Find the mobility of the electrons when the drift velocity is 23 units and the electric field is 11 units.

a) 1.1

b) 2.2

c) 3.2

d) 0.9

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8. Find the resistance of a cylinder of area 200 units and length 100m with conductivity of 12 units.

a) 1/24

b) 1/48

c) 1/12

d) 1/96

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9. Calculate the potential when a conductor of length 2m is having an electric field of 12.3units.

a) 26.4

b) 42.6

c) 64.2

d) 24.6

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10. On equating the generic form of current density equation and the point form of Ohm’s law, we can obtain V=IR. State True/False.

a) True

b) False