# Multiple choice question for engineering

## Set 1

1. The expression for conductance G of a coaxial transmission line with outer radius ‘b’ and inner radius ‘a’ is given by:

a) 2πωε”/ (ln b/a)

b) (R/2π)(1/a+1/b)

c) Rb/πa

d) 2Rb/a

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2. Expression for resistance R of a coaxial transmission line outer radius b and inner radius a is:

a) R_{s}/2π ( 1/a+1/b)

b) 2πω∈”/ln(b/a)

c) μ/π cos^{-1}(b/a)

d) πϵ’/cosh^{-1}(b/a)

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_{s}/2π ( 1/a+1/b). Here a and b are the outer and inner radius of the transmission line. Rs are the series resistance of the coaxial cable.

3. If the outer and the inner diameter of a coaxial transmission line are 20 mm and 10 mm respectively, then the inductance /m of the transmission line is:

a) 0.13 µH

b) 0.2 µH

c) 0.3 µH

d) 0.1 µH

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4. If the outer circumference and the inner circumference of a transmission line are 40π and 25π units respectively, then the capacitive reactance of the coaxial transmission line is:

a) 0.376 nF

b) 0.45 nF

c) 0.9 nF

d) none of the mentioned

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5. For a 2 wire transmission line, if the complex part of permittivity is 2.5, then the given distance between the 2 wires is 10mm and operated at a frequency of 1.2 MHz and the radius of the line being 5mm, then the conductance of the transmission line is:

a) 0.2 µH

b) 0.1 µH

c) 0.5 µH

d) 1 µH

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^{-1}(D/ 2a). Substituting the given values in the above equation, the conductance of the line is 0.2 µH.

6. Characteristics impedance of a coaxial line with external and inner diameter 5mm is:

a) 40 Ω

b) 41.58 Ω

c) 47.78 Ω

d) 54.87 Ω

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7. The characteristic impedance of the transmission line if the outer diameter and inner diameter of the transmission line is 20 mm and 10 mm respectively, given the intrinsic impedance of the medium is 377 Ω, then the characteristic impedance of the transmission line is:

a) 41.58 Ω

b) 50 Ω

c) 377 Ω

d) None of the mentioned

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8. Flow of power in transmission line takes place through:

a) Electric field and magnetic field

b) Voltage and current

c) Voltage

d) Electric field

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9. When a transmission line is exited by a source, total power supplied is delivered to the load.

a) True

b) False

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10. Expression for propagation constant. γ In terms of ω is:

a) √ω^{2}µ∈

b) ω^{2}µ∈

c) – ω^{2}µ∈

d) None of the mentioned

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## Set 2

1. In coupled line directional couplers, power from one line to another is transmitted through a microstrip line running between them.

a) true

b) false

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2. The number of conductors used in the construction of coupled line couplers is fixed.

a) true

b) false

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3. The mode of propagation of propagation supported by coupled line couplers is:

a) TM mode

b) TE mode

c) TEM mode

d) quasi TEM mode

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4. Coupled line couplers are:

a) symmetric couplers

b) asymmetric couplers

c) in phase couplers

d) type of hybrid coupler

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5. For coupled line coupler, if the voltage coupling factor is 0.1 and the characteristic impedance of the microstrip line is 50 Ω, even mode characteristic impedance is:

a) 50.23 Ω

b) 55.28 Ω

c) 100 Ω

d) 80.8 Ω

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_{0}√ (1+C) /√ (1-C).here C is the voltage coupling coefficient. Substituting the given values, even mode characteristic impedance is 55.28 Ω.

6. If the coupling coefficient of a coupled line coupler is 0.1 and the characteristic impedance of the material is 50 Ω, then the odd mode characteristic impedance is:

a) 45.23 Ω

b) 50 Ω

c) 38 Ω

d) none of the mentioned

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_{0}√ (1-C)/ √ (1+C). C is the voltage coupling co-efficient. Substituting the given values, odd mode characteristic impedance is 45.23.

7. Dielectric and conductor loss have no effect on the directivity of the coupled line coupler.

a) true

b) false

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8. Multisection couplers have a very narrow operational bandwidth which is a major disadvantage.

a) true

b) false

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9. Three section binomial couplers have very low directivity as compared to other coupler designs.

a) true

b) false

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10. The capacitance per unit length of broadside parallel lines with width W and separation d is:

a) ∈W/d

b) ∈d/W

c) dW/∈

d) none of the mentioned

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## Set 3

1. One condition to be satisfied in an oscillator circuit so that stable oscillations are produced is:

a) positive feedback is to be achieved

b) negative feedback is to be achieved

c) 180^{0} phase shift is required between the transistor input and output.

d) none of the mentioned

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^{0}of phase shift is to be achieved in the entire circuit to produce oscillations. The transistor used in the oscillator circuit must produce a phase shift of 180

^{0}to achieve stable oscillations. Hence this condition has to be satisfied by the oscillator.

2. In an oscillator, the resonant feedback circuit must have must have a low Q in order to achieve stable oscillation.

a) true

b) false

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3. Quartz crystals are more efficient as a feedback network because:

a) less circuit complexity

b) cost effective

c) crystals operate at high voltage levels

d) LC circuits have unloaded Q of a few hundreds

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^{0}.

4. Quartz crystal and tourmaline used in oscillators work on the principle of:

a) photo electric effect

b) piezo electric effect

c) Raman effect

d) black body radiation

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5. A quartz crystals equivalent circuit is a series LCR circuit and has a series resonant frequency.

a) true

b) false

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6. Quartz crystal is used in the _______region, where the operating point of the crystal is fixed.

a) resistive

b) inductive reactance

c) capacitive reactance

d) none of the mentioned

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7. In the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is:

a) capacitive

b) inductive

c) both capacitive and inductive

d) none of the mentioned

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8. In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is:

a) 0.25 MHz

b) 2.5 MHz

c) 25 MHz

d) 5 MHz

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9. Parallel resonant frequency of quartz crystal is given by:

a) 1/ √(LCₒC/(Cₒ+C))

b) 1/√LC

c) 1/√LCₒ

d) 1/ √(L(Cₒ+C) )

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10. The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:

a) 3 MHz

b) 0.3 MHz

c) 6 MHz

d) 9 MHz

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## Set 4

1. The stability of an oscillator is enhanced with the use of:

a) high Q tuning network

b) passive elements

c) appropriate feedback methods

d) none of the mentioned

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2. In oscillator tuning circuits, dielectric resonators are preferred over waveguide resonators because:

a) they have high Q factor

b) compact size

c) they are easily integrated with microwave integrated circuits

d) all of the mentioned

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3. A dielectric resonator coupled with an oscillator operates in:

a) TE_{10δ}

b) TE_{01δ}

c) TM_{10δ}

d) TM_{01δ}

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_{10δ}mode, and couples to the fringing field magnetic field of the microstrip line.

4. A dielectric resonator is modeled as __________ when it is used as a tuning circuit with a oscillator.

a) series RLC circuit

b) parallel RLC circuit

c) LC circuit

d) tank circuit

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5. The coupling factor between the resonator and the microstrip line is the ratio of external Q to the unloaded Q.

a) true

b) false

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^{2}R/2Z

_{0}.

6. If the reflection coefficient seen on the terminated microstrip line looking towards the resonator is 0.5, then the coupling coefficient is:

a) 0.5

b) 0.25

c) 0.234

d) 1

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7. A dielectric resonator can be incorporated into a circuit to provide _________ using either parallel or series arrangement.

a) frequency stability

b) oscillations

c) high gain

d) optimized reflection coefficient

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8. It is desired to design a frequency oscillator at 2.4 GHz and the reflection coefficient desired is 0.6, then the coupling coefficient between the feed line and the dielectric resonator is:

a) 1.5

b) 1

c) 0.5

d) none of the mentioned

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9. If the reflection coefficient between the feed line and the resonator is -0.6, then the equivalent impedance of the resonator at resonance given that the characteristic impedance of the microstrip line is:

a) 50 Ω

b) 12.5 Ω

c) 25 Ω

d) none of the mentioned

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_{0}(1 + Г)/(1- Г). Substituting the given values in this expression, equivalent impedance of the resonator is 12.5 Ω.

10. If the equivalent impedance of the resonator at resonance is 12.5 Ω and the characteristic impedance of the feed line is 50 Ω, then the coupling coefficient is:

a) 0.25

b) 0.5

c) 0.75

d) 1

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## Set 5

1. A dielectric material in the form of a small cube or disc can be used as a resonator.

a) true

b) false

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2. Dielectric resonators use materials that are less lossy.

a) true

b) false

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3. The major disadvantage of dielectric resonators is:

a) complex construction

b) field fringing

c) requirement of high dielectric constant

d) none of the mentioned

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4. One of the most commonly used dielectric materials is:

a) barium tetratetanate

b) titanium

c) teflon

d) none of the mentioned

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5. The resonant frequency of a dielectric resonator cannot be mechanically tuned.

a) true

b) false

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6. If a dielectric resonator has a dielectric constant of 49, then the reflection coefficient of the dielectric resonator is:

a) 0.5

b) 0.75

c) 0.1

d) 0.7

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_{r}-1)/ (√∈

_{r}-1). Given that dielectric constant is 49, the reflection coefficient is 0.75.

7. Q factor does not exist for dielectric resonator.

a) true

b) false

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8. The approximate loaded Q due to dielectric loss for a dielectric resonator given the loss tangent is 0.0001 is:

a) 1000

b) 500

c) 2000

d) 10000

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9. The direction of propagation is in z direction outside the dielectric in the resonator.

a) true

b) false

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10. A dielectric resonator is considered to be closed at both the ends.

a) true

b) false