# Multiple choice question for engineering

## Set 1

1. _________ is a non linear circuit that converts DC power to an AC waveform of desired frequency based on the oscillator design.

a) Attenuator

b) Amplifier

c) Oscillator

d) None of the mentioned

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2. The transfer function of an RF oscillator is given by:

a) A/ (1-AH (ω))

b) A/ (1+AH (ω))

c) A/ (-1+AH (ω))

d) 1/ (1-AH (ω))

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3. The criterion on which oscillations are produced in the oscillator circuit is called:

a) Shannon’s criteria

b) Barkhausen criteria

c) Colpitts criteria

d) None of the mentioned

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4. The necessary condition for oscillation in a Colpitts oscillator is:

a) C_{2}/C_{1}=g_{m}/G_{i}

b) C_{1}/C_{2}=g_{m}/G_{i}

c) C_{2}/C_{1}= g_{m}*G_{i}

d) None of the mentioned

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_{2}/C

_{1}= g

_{m}/G

_{i}. Here C

_{1}and C

_{2}are the capacitance in the feedback network, g

_{m}is the transconductance of the transistor and G

_{i}is the input admittance.

5. Colpitts oscillator operating at 50 MHz has an inductor in the feedback section of value 0.10µH. then the values of the capacitors in the feedback section is:

a) 100 pF, 100 pF

b) 100 pF, 50 pF

c) 70 pF, 130 pF

d) 80 pF, 60 pF

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^{2}L. This gives the equivalent capacitance value of 200 pF. C

_{1}C

_{2}/ (C

_{1}+C

_{2}) =200 pF. C

_{1}and C

_{2}values can be chosen in several ways. One of the way is C

_{1}=C

_{2}=100 pF.

6. The necessary condition for oscillation in a Hartley oscillator is:

a) L_{1}/L_{2} = g_{m}/G_{i}

b) L_{1}/L_{2} =G_{i} /g_{m}

c) L_{2}L/L_{1} = g_{m}/G_{i}

d) None of the mentioned

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_{1}/L

_{2}= g

_{m}/G

_{i}. Here, L

_{1}and L

_{2}are the inductances in the feedback network and g

_{m}is the transconductance of the transistor and G

_{i}is the input admittance.

7. An inductor is operating at frequency of 50 MHz. Its inductance is 0.1 µH, and then the series resistance associated with the inductor is: (Qo=100)

a) 0.31 Ω

b) 1.32 Ω

c) 1 Ω

d) 1.561 Ω

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8. Hartley oscillator has inductance values of 12 mH and 4 mH in the feedback section and a capacitor of 4 nF. Then the resonant frequency of the circuit is:

a) 19.89 kHz

b) 25 kHz

c) 45 kHz

d) 12 kHz

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_{1}(L

_{1}+ L

_{2})). Substituting the given values in the above equation, cut-off frequency is 19.89 kHz.

9. Colpitts oscillator in the feedback section has an inductance of 4 mH and capacitors of 12 nH and 4 nH. Then the resonant frequency of Colpitts oscillator is:

a) 50.4 kHz

b) 35.1 kHz

c) 45.9 kHz

d) None of the mentioned

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_{0}is the equivalent capacitance given by C

_{1}C

_{2}/ (C

_{1}+C

_{2}). Substituting and solving the equation, resonant frequency is 45.9 kHz.

10. For Colpitts oscillator, the capacitors C_{1} and C_{2} in the feedback network are 1 µF and 25 µF respectively. Then the β value of the transistor is:

a) 35

b) 000.76

c) 25

d) 0.0025

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_{2}/C

_{1}. Substituting the given values, β of the transistor is 25.

## Set 2

1. S parameters are expressed as a ratio of:

a) Voltage and current

b) Impedance at different ports

c) Indecent and the reflected voltage waves

d) None of the mentioned

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2. The relation between incident voltage matrix , reflected voltage matrix and S matrix for a microwave network:

a) [v-] = [s] [v+].

b) [v+] = [s] [v-].

c) [v-] [v] = [s].

d) [s] = [v] [v-].

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3. The specific element S_{ij} of the scattering matrix can be determined as:

a) S_{IJ}= V_{i-}/V_{j+}

b) S_{IJ}= V_{i+}/V_{j-}

c) S= V_{j+}/V_{i-}

d) None of the mentioned

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_{ij}is found by driving port j with an incident wave of voltage V

_{j+}coming out of ports i. The incident waves on all ports except the jth port are set to zero.

4. The device used to get the measurement of S parameters of n- port micro wave network is:

a) CRO

b) Network analyzer

c) Circulator

d) Attenuator

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5. For a one port network , the scattering parameter S₁₁ in terms of impedance parameter Z₁₁ is:

a) (Z_{11}-1)/ (Z_{11}+1)

b) (Z_{11}+1)/ (Z_{11}-1)

c) (Z_{11}+1) (Z_{11}-1)

d) Z_{11}

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_{11}coefficient. To compute the S

_{11}parameter of the network, the relation used is (Z

_{11}-1)/ (Z

_{11}+1).

6. Scattering matrix for a reciprocal network is:

a) Symmetric

b) Unitary

c) Skew symmetric

d) Identity matrix

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7. S₁₂=0.85-45⁰ and S₁₂=0.85 +45⁰ for a two port network. Then the two port network is:

a) Non-reciprocal

b) Lossless

c) Reciprocal

d) Lossy

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_{ij}=S

_{ji}. Since this condition is not satisfied in the above case, the matrix is non reciprocal.

8. Scattering matrix for a lossless matrix is:

a) Unitary

b) Symmetric

c) Identity matrix

d) Null matrix

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9. If the reflection co efficient of a 2 port network is 0.5 then the return network loss in the network is:

a) 6.5 dB

b) 0.15 dB

c) 6.020 dB

d) 10 dB

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10. If the reflection co efficient of a 2 port network is 0.25 then the return network loss in the network is:

a) 12.05 dB

b) 0.15 dB

c) 20 dB

d) 10 dB

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## Set 3

1. In a series LCR circuit, at resonance point the energy stored in the inductor and capacitor in the form of magnetic and electric energies are equal.

a) True

b) False

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2. Quality factor-Q of a resonant circuit signifies:

a) Loss in the resonant circuit

b) Gain in the resonant circuit

c) Magnetic energy stored in the circuit

d) Electric energy stored in the circuit

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3. The total energy stored in a series RLC circuit is equal to the energy stored in the inductor.

a) True

b) False

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4. Higher the quality factor of a series LCR circuit, greater is the operating bandwidth of the resonant circuit.

a) True

b) False

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5. The plot of input impedance magnitude v/s frequency has a peak at the resonant frequency.

a) True

b) False

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6. For a parallel resonance circuit, the plot of input impedance magnitude v/s frequency has a dip at the resonant frequency.

a) True

b) False

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7. The relation between unloaded Q and external Q is:

a) External Q> unloaded Q

b) Unloaded Q> external Q

c) External Q = unloaded Q

d) None of the mentioned

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8. Loaded Q and External Q are 2 different parameters.

a) True

b) False

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9. The bandwidth of a series RLC circuit is 200 Hz. Then the quality factor of the circuit is:

a) 200

b) 100

c) 0.005

d) 0.5

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10. If a parallel RLC circuit is excited with a source of 8v, 50 Hz and the circuit has an inductor of 1mH, capacitor of 1µF and a resistor of 50Ω, then the power loss that occurs in the circuit is:

a) 6.4mW

b) 3.2mW

c) 12.8mV

d) None of the mentioned

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^{2}/R. given the values of source voltage and resistance in the circuit, the power loss in the parallel RLC circuit is 6.4mW.

## Set 4

1. The major advantage of single stub tuning over other impedance matching techniques is:

a) Lumped elements are avoided

b) It can be fabricated as a part of transmission line media

c) It involves two adjustable parameters

d) All of the mentioned

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2. Shunt stubs are preferred for:

a) Strip and microstrip lines

b) Coplanar waveguides

c) Circular waveguide

d) Circulators

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3. The two adjustable parameters in single stub matching are distance‘d’ from the load to the stub position, and _________

a) Susceptance or reactance provided by the stub

b) Length of the stub

c) Distance of the stub from the generator

d) None of the mentioned

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4. In shunt stub matching, the key parameter used for matching is:

a) Admittance of the line at a point

b) Admittance of the load

c) Impedance of the stub

d) Impedance of the load

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5. For series stub matching, the parameter used for matching is:

a) Impedance of the transmission line at a point

b) Voltage at a point on the transmission line

c) Admittance at a point on the transmission line

d) Admittance of the load

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6. For co-axial lines and waveguides, ________ is more preferred.

a) Open circuited stub

b) Short circuited stub

c) Slotted section

d) Co-axial lines cannot be impedance matched

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7. For a load impedance of ZL=60-j80. Design of 2 single-stub shunt tuning networks to match this load to a 50Ω line is to be done. What is the normalized admittance obtained so as to plot it on smith chart?

a) 1+j

b) 0.3+j0.4

c) 0.4+j0.3

d) 0.3-j0.4

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8. If the normalized admittance at a point on a transmission line to be matched is 1+j1.47. Then the normalized susceptance of the stub used for shunt stub matching is:

a) 1Ω

b) 1.47 Ω

c) -1.47 Ω

d) -1 Ω

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9. After impedance matching, if a graph is plot with frequency v/s reflection co-efficient of the transmission line is done, then at the frequency point for which the design is done, which of the following is true?

a) There is a peak at this point of the curve

b) There is a dip at this point of the curve

c) The curve is a straight line

d) Such a plot cannot be obtained

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10. In series stub matching, if the normalized impedance at a point on the transmission line to be matched is 1+j1.33. Then the reactance of the series stub used for matching is:

a) 1 Ω

b) -1.33 Ω

c) -1 Ω

d) 1.33 Ω

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## Set 5

1. Smith chart is based on the polar plot of:

a) Reactance

b) Voltage

c) Current

d) Voltage reflection co-efficient

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^{jθ}. Magnitude is plotted as radius from the center of the chart, and the angle is measured in counter clockwise direction from the right hand side. Hence, smith chart is based on the polar pot of voltage reflection co-efficient.

2. Any passively realizable reflection coefficient can be plotted as a unique point on the smith chart. This statement implies that:

a) Reflection co-efficient less than or equal to 1 can be plotted

b) Reflection co-efficient greater than or equal to 1 can be plotted

c) Transmission co-efficient has to be less than or equal to one for the point to be located

d) T=Г+1

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3. Reflection coefficient of a transmission line in its polar form can be represented as:

a) ┌=|┌|e^{jθ}

b) ┌=|┌|e^{jθ-1}

c) ┌=|┌|e^{jθ+1}

d) ┌=|┌|e^{jθ+α}

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^{jθ}, Consisting of both magnitude and phase θ.

4. If the characteristic impedance of a ƛ/2 transmission line is 50 Ω and reflection coefficient 0.3, then its input impedance

a) 26.92 Ω

b) 30 Ω

c) 40 Ω

d) 34.87 Ω

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^{-2jβL})/ (1- Г

^{e-2jβL}). Substituting the given values, the input impedance of the line is 26.92 Ω

5. If the normalized input impedance of a transmission line is 0.5 Ω, then he reflection coefficient of a ƛ/2 transmission line is

a) 0.3334

b) 0.5

c) 0.6667

d) 1

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^{-2jβL})/ (1- Г

^{e-2jβL}). Substituting the given values in the above equation, reflection coefficient is 0.3334.

6. If the input impedance of a ƛ/2 transmission line is 100 Ω with a voltage reflection coefficient of 0.344, then the characteristic impedance of the transmission line is:

a) 200 Ω

b) 100 Ω

c) 50 Ω

d) None of the mentioned

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^{-2jβL})/ (1- Г

^{e-2jβL}). Substituting the given values in the above equation, characteristic impedance of the transmission line is 200 Ω.

7. Normalized impedance of 0.3+j0.4 lies in the:

a) Upper half of the impedance smith chart

b) Lower half of the impedance smith chart

c) Horizontal line of the chart

d) None of the mentioned

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8. Normalized impedance of 1-j is:

a) In the upper half of the impedance smith chart

b) In the Lower half of the impedance smith chart

c) On the outer most circle of the smith chart.

d) On the horizontal line of the smith chart

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9. If a transmission line of a characteristic impedance 100 Ω is terminated with a load impedance of 300+j200 Ω, then the normalized load impedance is:

a) 1+j

b) 1-j

c) 3+2j

d) 2-3j

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10. If the normalized load impedance of a transmission line is 0.3-j0.4 with a characteristic impedance of 50 Ω, then the load impedance is:

a) 15-j20

b) 15+j20

c) 1-j

d) 0.3-0.4j

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11. To get an admittance chart from an impedance chart:

a) Smith chart has to be rotated by 90⁰

b) Smith chart has to be rotated by 180⁰

c) Admittance chart cannot be obtained from the impedance chart anyway.

d) None of the mentioned