# Multiple choice question for engineering

## Set 1

1. The value of ‘α’ for a lossless line is:

a) 0

b) 1

c) Infinity

d) Data insufficient

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2. If propagation constant is 12:60°, then the value of phase constant and attenuation constant is:

a) α=6, β=10.39

b) α=61, β=78

c) α=12, β=20.6

d) none of the mentioned

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3. If a transmission line with inductive reactance of 41.97 Ω and capacitive reactance of 1132.5Ω is operated at 1 GHz , then its phase constant is:

a) 0.0305

b) 0.3

c) 30.3

d) 0.6

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_{L}=2πfL and X

_{c}= 1/2πfC. β=ω√LC, substituting the calculated L and C, we get β=0.0305.

4. The expression for a phase velocity of a transmission line is:

a) √LC

b) 1/√LC

c) X_{L}+X_{c}

d) X_{L}/X_{c}

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5. If the admittance and the impedance of a transmission line are 100 Ω and 50 Ω of a respectively, then value of phase constant β is:

a) 0

b) 20

c) 132

d) 50

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6. For a lossless line, which of the following is true?

a) γ=jβ

b) γ=α

c) γ=α+jβ

d) γ=α*jβ

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7. Expression for phase constant β is:

a) √LC

b) ω √LC

c)1/ (ω √LC)

d) None of the mentioned

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8. A microwave generator at 1.2 GHz supplies power to a microwave transmission line having the parameters R=0.8Ω/m, G=O.8millisiemen/m, L=0.01µH/m and C=0.4PF/m. Propagation constant of the transmission line is:

a) 0.0654 +j0.48

b) 0.064+j4.8

c) 6.4+j4.8

d) none of the mentioned

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9. In a certain microwave transmission line, the characteristic impedance was found to be 210 10°Ω and propagation constant 0.2 78°.What is the impedance Z of the line, if the frequency of operation is 1 GHz?

a) 0.035+j41.97

b) 0.35+j4.97

c) 35.6+j4.28

d) 9.254+j4.6

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10. For a transmission line, L=1.8mh/m C=0.01pF/m, then the phase constant of the line when operated at a frequency of 1 GHz is:

a) 4.2426

b) 2.2

c) 0.3

d) 1

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## Set 2

1. For a low loss line when both conductor and di-electric loss is small, the assumption that could be made is:

a) R < < ωL and G < < ωC

b) R > > ωL and G > >ωC

c) R < <ωC and G < < ωL

d) R > >ωC and G > >ωL

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2. Expression for α(attenuation constant) in terms of R , G, L and C of a transmission line is:

a) (R√(C/L)+G√(L/C))0.5

b) (R√(C/L)+G√(L/C))

c) (R√(L/C)+G√(C/L))

d) (R√(L/C)+G√(C/L))0.5

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3. Expression for characteristic impedance Zₒ of a transmission line in terms of L and C the transmission line is:

a) √(C/L)

b) √(CL)

c) √(L/C)

d) 1/√(LC)

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4. If the inductance and capacitance of a loss line transmission line are 45 mH/m and10 µF/m, the characteristic impedance of the transmission line is:

a) 50Ω

b) 67.08Ω

c) 100Ω

d) none of the mentioned

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5. If the characteristic impedance of a transmission line is 50 Ω, and the inductance of the transmission line being 25 mH/m, the capacitance of the lossy transmission line is:

a) 1µF

b) 10 µF

c) 0.1 µF

d) 50 µF

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6. If R = 1.5Ω/m, G = 0.2 mseimens/m, L = 2.5 nH/m, C = 0.1 pF/m for a low loss transmission line, then the attenuation constant of the transmission line is:

a) 0.0.158

b) 0.0523

c) 0.0216

d) 0.0745

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7. A lossy line that has a linear phase factor as a function of frequency is called:

a) distortion less line

b) terminated lossy line

c) loss less line

d) lossy line

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8. The condition for a distortion less line is:

a) R/L=G/C

b) R/C=G/L

c) R=G

d) C=L

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9. For a distortion less line, R= 0.8Ω/m, G= 0.8 msiemens/m, L= 0.01µH/m then C is:

a) 10 pF

b) 1pF

c) 1nF

d) 10nF

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10. For a lossy transmission line, γ=0.02+j0.15 and is 20m long. The line is terminated with an impedance of a 400Ω. Then the input impedance of the transmission line given that the characteristic impedance of the transmission line is 156.13+j11.38Ω is:

a) 100+j50 Ω

b) 228+j36.8 Ω

c) 50+36.8j Ω

d) none of the mentioned

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## Set 3

1. Micro strip can be fabricated using:

a) Photo lithographic process

b) Electrochemical process

c) Mechanical methods

d) None of the mentioned

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2. The mode of propagation in a microstrip line is:

a) Quasi TEM mode

b) TEM mode

c) TM mode

d) TE mode

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3. Microstrip line can support a pure TEM wave.

a) True

b) False

c) Microstrip supports only TM mode

d) Microstrip supports only TE mode

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4. The effective di electric constant of a microstrip line is:

a) Equal to one

b) Equal to the permittivity of the material

c) Cannot be predicted

d) Lies between 1 and the relative permittivity of the micro strip line

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_{r}+ 1)/2 + (∈

_{r}-1)/2 * 1/ (√1+12d/w). Along with the relative permittivity, the effective permittivity also depends on the effective width and thickness of the microstrip line.

5. Effective dielectric constant of a microstrip is given by:

a) (∈_{r} + 1)/2 + (∈_{r}-1)/2 * 1/ (√1+12d/w)

b) (∈_{r}+1)/2 + (∈_{r}-1)/2

c) (∈_{r}+1)/2 (1/√1+12d/w)

d) (∈_{r} + 1)/2-(∈_{r}-1)/2

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_{r}+ 1)/2 + (∈

_{r}-1)/2 * 1/ (√1+12d/w). This relation clearly shows that the effective permittivity is a function of various parameters of a microstrip line, the relative permittivity, effective width and the thickness of the substrate.

6. The effective dielectric constant of a micro strip line is 2.4, then the phase velocity in the micro strip line is given by:

a) 1.5*10^{8} m/s

b) 1.936*10^{8} m/s

c) 3*10^{8} m/s

d) None of the mentioned

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_{r}. substituting the value of relative permittivity and the speed of light in vacuum, the phase velocity is 1.936*10

^{8}m/s.

7. The effective di electric constant of a micro strip line with relative permittivity being equal to 2.6, with a width of 5mm and thickness equal to 8mm is given by:

a) 2.6

b) 1.97

c) 1

d) 2.43

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_{r}+ 1)/2 + (∈

_{r}-1)/2 * 1/ (√1+12d/w). Substituting the given values of relative permittivity, effective width, and thickness, the effective dielectric constant is 1.97.

8. If the wave number of an EM wave is 301/m in air , then the propagation constant β on a micro strip line with effective di electric constant 2.8 is:

a) 602

b) 503.669

c) 150

d) 200

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_{0}√∈

_{e}. ∈

_{e}is the effective dielectric constant. Substituting the relevant values, the effective dielectric constant is 503.669.

9. For most of the micro strip substrates:

a) Conductor loss is more significant than di electric loss

b) Di electric loss is more significant than conductor loss

c) Conductor loss is not significant

d) Di-electric loss is less significant

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10. The wave number in air for EM wave propagating on a micro strip line operating at 10GHz is given by:

a) 200

b) 211

c) 312

d) 209

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11. The effective dielectric constant ∈_{r} for a microstrip line:

a) Varies with frequency

b) Independent of frequency

c) It is a constant for a certain material

d) Depends on the material used to make microstrip

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_{r}+ 1)/2 + (∈

_{r}-1)/2 * 1/ (√1+12d/w). The equation clearly indicates that the effective dielectric constant is independent of the frequency of operation, but depends only on the design parameters of a microstrip line.

12. With an increase in the operating frequency of a micro strip line, the effective di electric constant of a micro strip line:

a) Increases

b) Decreases

c) Independent of frequency

d) Depends on the material of the substrate used as the microstrip line

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## Set 4

1. In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.

a) True

b) False

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2. Any device with negative impedance as its characteristic property can be called:

a) Energy source

b) Energy sink

c) Oscillator

d) None of the mentioned

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_{in}+ X

_{L}=0 controls the frequency of oscillation. X

_{in}is the impedance of the negative resistance device.

3. In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.

a) True

b) False

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_{in}=-Z

_{L}. Since this condition is satisfied in the above case, steady state oscillation is achieved.

4. For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:

a) Г_{in}=Г_{L}

b) Г_{in}=-Г_{L}

c) Г_{in}=1/Г_{L}

d) None of the mentioned

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_{in}=1/Г

_{L}. Here Г

_{in}is the reflection coefficient towards the reflection coefficient device and Г

_{L}is the reflection coefficient towards the load.

5. A one port oscillator uses a negative resistance diode having Г_{in}=0.9575+j0.8034 (Z0=50Ω) at its desired frequency point. Then the input impedance of the diode is:

a) -44+j123

b) 50+j100

c) -44+j145

d) None of the mentioned

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_{in})/ (1-Г

_{in}). Substituting in the given equation, the input impedance is -44 +j123 Ω.

6. If the input impedance of a diode used in the microwave oscillator is 45-j23 Ω, then the load impedance is to achieve stable oscillation is:

a) 45-j23 Ω

b) -45+j23 Ω

c) 50 Ω

d) 23-j45 Ω

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_{in}=-Z

_{L}. According to this equation, the load impedance required for stabilized oscillation is – (45-j23) Ω. The load impedance is thus -45+j23 Ω.

7. To achieve stable oscillation, Z_{in} + Z_{L}=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.

a) True

b) False

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_{in}+ Z

_{L}=0 is only a necessary condition for stable oscillation and not sufficient. Stability requires that any perturbation in current or frequency is damped out, allowing the oscillator to return to its original state.

8. In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.

a) True

b) False

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9. In transistor oscillators, FET and BJT are used. Instability is achieved by:

a) Giving a negative feedback

b) Giving a positive feedback

c) Using a tank circuit

d) None of the mentioned

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10. In a transistor amplifier, if the input impedance is -84-j1.9 Ω, then the terminating impedance required to create enough instability is:

a) -84-j1.9 Ω

b) 28+j1.9 Ω

c) – (28+j1.9) Ω

d) None of the mentioned

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_{s}=-R

_{in}/3. Z

_{s}is the terminating impedance. Substituting in the given equation, the terminated impedance is 28+j1.9 Ω.

## Set 5

1. The production of power at higher frequencies is much simpler than production of power at low frequencies.

a) True

b) False

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2. Microwave tubes are power sources themselves at higher frequencies and can be used independently without any other devices.

a) True

b) False

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3. Microwave tubes are grouped into two categories depending on the type of:

a) Electron beam field interaction

b) Amplification method

c) Power gain achieved

d) Construction methods

d) None of the mentioned

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4. The klystron tube used in a klystron amplifier is a _________ type beam amplifier.

a) Linear beam

b) Crossed field

c) Parallel field

d) None of the mentioned

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5. In crossed field tubes, the electron beam traverses the length of the tube and is parallel to the electric field.

a) True

b) False

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6. ________ is a single cavity klystron tube that operates as on oscillator by using a reflector electrode after the cavity.

a) Backward wave oscillator

b) Reflex klystron

c) Travelling wave tube

d) Magnetrons

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7. A major disadvantage of klystron amplifier is:

a) Low power gain

b) Low bandwidth

c) High source power

d) Design complexity

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8. In a _________ oscillator, the RF wave travels along the helix from the collector towards the electron gun.

a) Interaction oscillator

b) Backward wave oscillator

c) Magnetrons

d) None o the mentioned

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9. Extended interaction oscillator is a ________ beam oscillator that is similar to klystron.

a) Linear beam

b) Crossed beam

c) Parallel beam

d) M beam

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10. Magnetrons are microwave devices that offer very high efficiencies of about 80%.

a) True

b) False

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11. Klystron amplifiers have high noise output as compared to crossed field amplifiers.

a) True

b) False

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12. ____________ is a microwave device in which the frequency of operation is determined by the biasing field strength.

a) VTM

b) Gyratron

c) Helix BWO

d) None of the mentioned