# Multiple choice question for engineering

## Set 1

Circuit for Q.1-Q.2

1. Vth = ?

a) 1 V

b) 2 V

c) 3 V

d) 4 V

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2. Rth = ? (in ohm)

a) 2

b) 3

c) 4

d) 5

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3. A battery has a short-circuit current of 30 A and an open circuit voltage of 24 V. If the battery is connected to an electric bulb of resistance 2 ohm^{-1}, the power dissipated by the bulb is

a) 80 W

b) 1800 W

c) 112.5 W

d) 228 W

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Circuit for Q.4-Q-5

4. In = ?

a) 1.5 A

b) 3 A

c) 6 A

d) 10 A

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5. Rn = ? (in ohm)

a) 10/3

b) 4

c) 6

d) 10

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Circuit for (Q.6-Q.7)

6. Vth = ?

a) -2 V

b) -1 V

c) 1 v

d) 2 V

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7. Rth = ? (in ohm)

a) 5/6

b) 6/5

c) 5/3

d) 3/5

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8. The equivalent to the given circuit is

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9. V1 = ?

a) 6 V

b) 7 V

c) 8 V

d) 10 V

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10. i1 = ?

a) 3 A

b) 0.75 mA

c) 2 mA

d) 1.75 mA

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## Set 2

1. In a receiver the input signal is 100 V, while the internal noise at the input is 10 V. With amplification the output signal is 2 V, while the output noise is 0.4 V. The noise figure of receiver is

a) 2

b) 0.5

c) 0.2

d) None of the mentioned

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2. A receiver is operated at a temperature of 300 K. The transistor used in the receiver have an average output resistance of 1 k. The Johnson noise voltage for a receiver with a bandwidth of 200 kHz is

a) 1.8 µV

b) 8.4 µV

c) 4.3 µV

d) 12.6 µV

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^{2}= 4kBTR where symbols have their usual meanings, hence v = 1.8 µV.

3. A resistor R 1 k is maintained at 17C. The rms noise voltage generated in a bandwidth of 10 kHz is

a) 16 x 10^{(-14)} V

b) 0.4 µV

c) 4 µV

d) 16 x 10^{(-18)} V

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^{2}= 4kBTR where symbols have their usual meanings, hence v = 0.4 µV.

4. A mixer stage has a noise figure of 20 dB. This mixer stage is preceded by an amplifier which has a noise figure of 9 dB and an available power gain of 15 dB. The overall noise figure referred to the input is

a) 11.07

b) 18.23

c) 56.43

d) 97.38

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5. A system has three stage cascaded amplifier each stage having a power gain of 10 dB and noise figure of 6 dB. the overall noise figure is

a) 1.38

b) 6.8

c) 4.33

d) 10.43

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(Q.6-Q.8) An amplifier when used with a source of average noise temperature 60 K, has an average operating noise figure of 5.

6. The Te is

a) 70 K

b) 110 K

c) 149 K

d) 240 K

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7. If the amplifier is sold to engineering public, the noise figure that would be quoted in a catalog is

a) 0.46

b) 0.94

c) 1.83

d) 2.93

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8. What average operating noise figure results when the amplifier is used with an antenna of temperature 30 K?

a) 9.54 db

b) 10.96 db

c) 11.23 db

d) 12.96 db

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9. What is the maximum average effective input noise temperature that an amplifier can have if its average standard noise figure is to not exceed 1.7?

a) 203 K

b) 215 K

c) 235 K

d) 255 K

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10. If a matched attenuator with a loss of 3.2 dB is placed between the source and the amplifier’s input, what is the operating spot noise figure of the attenuator amplifier cascade if the attenuator’s physical temperature is 290 K?

a) 9 db

b) 11.3 db

c) 10.4 db

d) 13.3 db

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## Set 3

1. In the non-inverting configuration of operational amplifier

a) The positive terminal is connected to the ground directly

b) The negative terminal is connected to the ground directly

c) The positive terminal is connected to the power source

d) The negative terminal is connected to the power source

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2. For ideal non-inverting operational amplifier

a) Input and output resistances are infinite

b) Input resistance is infinite and output resistance is zero

c) Input resistance is zero and output resistance is infinite

d) Input and output resistances are zero

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3. For an ideal non-inverting operational amplifier having finite gain (A), the ratio of output voltage (v_{0}) to input voltage (v_{i}) is (given R_{2} is the feedback resistance)

a) (1+R2/R1)/(1+((1+R2/R1)/A))

b) (R2/R1)/(((1+R2/R1)/A))

c) (1+R2/R1)/(((1+R2/R1)/A))

d) (R2/R1)/(1+((1+R2/R1)/A))

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4. The gain for an ideal non-inverting operational amplifier is (given R_{2} is the feedback resistance)

a) R_{2}/R_{1} – 1

b) R_{2}/R_{1}

c) -R_{2}/R_{1}

d) R_{2}/R_{1} + 1

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5. While performing an experiment to determine the gain for an ideal operational amplifier having finite gain, a student mistakenly used the equation 1 + R_{2}/R_{1} where R_{2} is the feedback resistance. What is the percentage error in his result? Given A is the finite voltage gain of the ideal amplifier used.

a) (R2/R1)/(A+ R2/R1) X 100%

b) (1+R2/R1)/(A+R2/R1) X 100%

c) (1+R2/R1)/(A+1+R2/R1) X 100%

d) (R2/R1)/(A+1+R2/R1) X 100%

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6. The finite voltage gain of a non-inverting operational amplifier is A and the resistance used is R_{1} and R_{2} in which R_{2} is the feedback resistance. Under what conditions it can one use the expression 1 + R_{2}/R_{1} to determine the gain of the amplifier?

a) A ~ R_{2}/R_{1}

b) A >> R_{2}/R_{1}

c) A << R_{2}/R_{1}

d) None of the mentioned

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_{2}/R

_{1}.

7. Which of the following is not true for a voltage follower amplifier?

a) Input voltage is equal to output voltage

b) Input resistance is infinite and output resistance is zero

c) It has 100% negative feedback

d) None of the mentioned

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8. For designing a non-inverting amplifier with a gain of 2 at the maximum output voltage of 10 V and the current in the voltage divider is to be 10 μA the resistance required are R_{1} and R_{2} where R_{2} is used to provide negative feedback. Then

a) R_{1} = 0.5 MΩ and R_{2} = 0.5 MΩ

b) R_{1} = 0.5 kΩ and R_{2} = 0.5 kΩ

c) R_{1} = 5 MΩ and R_{2} = 5 MΩ

d) R_{1} = 5 kΩ and R_{2} = 5 kΩ

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_{1}= 2 and 10/(R

_{1}+R

_{2}) = 10 μA. Solve for R

_{1}and R

_{2}.

9. It is required to connect a transducer having an open-circuit voltage of 1 V and a source resistance of 1 MΩ to a load of 1-kΩ resistance. Find the load voltage if the connection is done (a) directly and (b) through a unity-gain voltage follower.

a) 1 μV and 1 mV respectively

b) 1 mV and 1 V respectively

c) 0.1 μV and 0.1 mV respectively

d) 0.1 mV and 0.1 V respectively

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10. Consider the figure given below. If the resistance R_{1} is disconnected from the ground and connected to a third power source v_{3}, then expression for the value of

v_{0} is

a) 2v_{1} + 4v_{2} − 3v_{3}

b) 6v_{1} + 8v_{2} − 3v_{3}

c) 6v_{1} + 4v_{2} − 9v_{3}

d) 3v_{1} + 4v_{2} − 3v_{3}

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## Set 4

1. Slew rate of an amplifier is defined as

a) Minimum rate of change of the output possible in a real operational amplifier

b) Maximum rate of change of the output possible in a real operational amplifier

c) Average rate of change of the output possible in a real operational amplifier

d) Ratio of the maximum and the average rate of change of the output in a real amplifier

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2. Determine the slew rate of the amplifier having full power bandwidth f_{0} and the rated output voltage as V_{0}. Given that the input signal is of sinusoidal nature.

a) 2πf_{0} V_{0}

b) V_{0} / 2πf_{0}

c) V_{0} / f_{0}

d) f_{0} V_{0}

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_{0}sin wt dv/dt = wV

_{0}sin wt max value of dv/dt = wV

_{0}max value of w = w

_{0}= 2πf

_{0}w

_{0}V

_{0}= Slew Rate = 2πf

_{0}V

_{0}.

3. The units of the full power bandwidth is

a) Watt

b) Joule

c) Seconds

d) Hertz

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4. The full-power bandwidth, f_{M}, is the maximum frequency at which

a) an output sinusoid with an amplitude equal to the op-amp rated output voltage (V_{o max}) can be produced without distortion

b) it is the range of the frequencies in which the amplitude of output signal is equal to or greater than half of the op-amp rated output voltage

c) it is the range of the frequencies in which the amplitude of output signal is equal to or less than half of the op-amp rated output voltage

d) It is the range of the frequencies in which the power gain is half or more than half of the maximum rated power gain of the op-amp

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5. Which of the following is not limitation of the operational amplifier

a) Output voltage saturation

b) Output current limits

c) Slew rate

d) None of the mentioned

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6. A particular op amp using ±15-V supplies operates linearly for outputs in the range −12 V to +12 V. If used in an inverting amplifier configuration of gain –100, what is the rms value of the largest possible sine wave that can be applied at the input without output clipping?

a) 120 mV

b) 60 mV

c) 84.85 mV

d) 42.42 mV

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7. For operation with 10-V output pulses with the requirement that the sum of the rise and fall times represent only 20% of the pulse width (at half amplitude), what is the slew-rate requirement for an op amp to handle pulses 2 µs wide? (Note: The rise and fall times of a pulse signal are usually measured between the 10%- and 90%-height points.)

a) 10 V/µs

b) 20 V/µs

c) 40 V/µs

d) 80 V/µs

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8. An op amp having a slew rate of 20 V/µs is to be used in the unity-gain follower configuration, with input pulses that rise from 0 to 3 V. What is the shortest pulse that can be used while ensuring full-amplitude output?

a) 0.10 µs

b) 0.15 µs

c) 0.20 µs

d) 0.30 µs

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(Q.9-Q.10) In designing with op amps one has to check the limitations on the voltage and frequency ranges of operation of the closed-loop amplifier, imposed by the op-amp finite bandwidth (f_{t}), slew rate (SR), and output saturation (V_{o max}). Consider the use of an op amp with ft_{t} = 2 MHz, SR = 1 V/µs, and V_{0 max }= 10 V in the design of a non-inverting amplifier with a nominal gain of 10. Assume a sine-wave input with peak amplitude Vi.

9. If Vi = 0.5 V, what is the maximum frequency before the output distorts?

a) 31.8 kHz

b) 318 kHz

c) 3.18 kHz

d) 3.18 MHz

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_{i}= 0.5v, V

_{0}= 0.5 X 10 = 5V 2πf V

_{0}= SR or f = 31.8 kHz.

10. If f = 20 kHz, what is the maximum value of V_{i} before the output distorts?

a) 0.397 V

b) 0.795 V

c) 1.192 V

d) 1.590 V

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_{0}= 10Vi 2πf V

_{0}= SR = 20πf V

_{i}, here f is 20 kHz, SR is 1 V/µs. Hence the value of V

_{i}is 0.795 V.

## Set 5

1. What is the thickness of ‘space charge region’ or ‘transition region’ in P-N junction diode?

a) 1 micron

b) 5 micron

c) 10 micron

d) 2.876 micron

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^{-4}cm = 10

^{-6}m= 1 micron.

2. If what of the following is doped into a semiconductor say germanium a P-N junction is formed.

a) Electrons and Protons

b) Protons and Neutrons

c) Neutrons and Electrons

d) Gallium and Phosphorus

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3. Which of the factors doesn’t change the diode current.

a) Temperature

b) External voltage applied to the diode

c) Boltzmann‘s constant

d) Resistance

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^{(v/nVt)}-1], as shown in this equation the diode current is dependent on temperature , voltage applied on the diode , Boltzmann’s constant but diode current is not dependent on resistance as it is independent of resistance.

4. The product of mobility of the charge carriers and applied Electric field intensity is known as

a) Drain velocity

b) Drift velocity

c) Push velocity

d) Pull velocity

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5. The tendency of charge carriers to move from a region of heavily concentrated charges to region of less concentrated charge is known as.

a) Depletion current

b) Drain current

c) Diffusion current

d) Saturation current

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6. If the drift current is 100mA and diffusion current is 1A what is the total current in the semiconductor diode.

a) 1.01 A

b) 1.1 A

c) 900m A

d) 10 A

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7. Which of the following is reverse biased?

a) A)

b) B)

c) C)

d) D)

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8. The drift velocity is 5V and the applied electric field intensity 20v/m what will be the mobility of charge carriers.

a) 100 m^{2}/ (vs)

b) 4 m^{2}/ (vs)

c) 15 m^{2}/ (vs)

d) 0.25 m^{2}/ (vs)

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9. When there is an open circuit what will be the net hole current.

a) 5A

b) 0.05A

c) 0.5A

d) 0A

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10. Rate of change of concentration per unit length in a semiconductor is called as.

a) Concentration change

b) Concentration mixture

c) Concentration gradient

d) Concentration variant