# Multiple choice question for engineering

## Set 1

1. Efficiency of a centre tapped full wave rectifier is _________

a) 50%

b) 46%

c) 70%

d) 81.2%

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2. A full wave rectifier supplies a load of 1KΩ. The AC voltage applied to diodes is 220V (rms). If diode resistance is neglected, what is the ripple voltage?

a) 0.562V

b) 0.785V

c) 0.954V

d) 0.344V

### View Answer

_{ϒ})

_{RMS}=ϒV

_{DC}/100. V

_{DC}=0.636*V

_{RMS}* √2=0.636*220* √2=198V and ripple factor ϒ for full wave rectifier is 0.482. Hence, (V

_{ϒ})

_{RMS}=0.482*198 /100=0.954V.

3. A full wave rectifier delivers 50W to a load of 200Ω. If the ripple factor is 2%, calculate the AC ripple across the load.

a) 2V

b) 5V

c) 4V

d) 1V

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_{DC}=V

_{DC}

^{2}/R

_{L}. So, V

_{DC}=(P

_{DC}*RL)

^{1/2}=10000

^{1/2}=100V. Here, ϒ=0.02 ϒ=V

_{AC}/V

_{DC}=V

_{AC}/100.So, V

_{AC}=0.02*100=2V.

4. A full wave rectifier uses load resistor of 1500Ω. Assume the diodes have R_{f}=10Ω, R_{r}=∞. The voltage applied to diode is 30V with a frequency of 50Hz. Calculate the AC power input.

a) 368.98mW

b) 275.2mW

c) 145.76mW

d) 456.78mW

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_{IN}=I

_{RMS}

^{2}(R

_{F}+R

_{r}). I

_{RMS}=I

_{m}/√2=V

_{m}/(R

_{f}+R

_{L})√2=30/(1500+10)*1.414=13.5mA So, P

_{IN}=(13.5*10-3)2*(1500+10)=275.2mW.

5. In a centre tapped full wave rectifier, R_{L}=1KΩ and for diode Rf=10Ω. The primary voltage is 800sinωt with transformer turns ratio=2. The ripple factor will be _________

a) 54%

b) 48%

c) 26%

d) 81%

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_{RMS}/I

_{AVG})

^{2}– 1]

^{1/2}. I

_{RMS}=I

_{m}/√2=V

_{m}/(R

_{f}+R

_{L})√2=200/1.01=198. (Secondary line to line voltage is 800/2=400. Due to centre tap V

_{m}=400/2=200) I

_{RMS}=198/√2=140mA, I

_{AVG}=2*198/π=126mA. ϒ=[(140/126)

^{2}-1]

^{1/2}=0.48. So, ϒ=48%.

6. If input frequency is 50Hz for a full wave rectifier, the ripple frequency of it would be _________

a) 100Hz

b) 50Hz

c) 25Hz

d) 500Hz

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7. Transformer utilization factor of a centre tapped full wave rectifier is_________

a) 0.623

b) 0.678

c) 0.693

d) 0.625

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8. In the circuits given below, the correct full wave rectifier is _________

a)

b)

c)

d)

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9. If the peak voltage on a centre tapped full wave rectifier circuit is 5V and diode cut in voltage is 0.7. The peak inverse voltage on diode is_________

a) 4.3V

b) 9.3V

c) 5.7V

d) 10.7V

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_{m}-V

_{d}= 10-0.7 = 9.3V.

10. In a centre tapped full wave rectifier, the input sine wave is 250sin100t. The output ripple frequency will be _________

a) 50Hz

b) 100Hz

c) 25Hz

d) 200Hz

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_{m}sinωt. So, by comparing we get ω=100. Frequency, f =ω/2=50Hz. The output of centre tapped full wave rectifier has double the frequency of inpu. Hence, f

_{out}= 100Hz.

## Set 2

1. The diode in a half wave rectifier has a forward resistance RF. The voltage is V_{m}sinωt and the load resistance is RL. The DC current is given by _________

a) V_{m}/√2R_{L}

b) V_{m}/(R_{F}+R_{L})π

c) 2V_{m}/√π

d) V_{m}/R_{L}

### View Answer

_{DC}=I

_{AVG}=I

_{m}/π I= V

_{m}sinωt/(R

_{F}+R

_{L})=I

_{m}sinωt I

_{m}=V

_{m}/ R

_{F}+R

_{L}So, I

_{DC}=I

_{m}/π=V

_{m}/(R

_{F}+R

_{L}).

2. The below figure arrives to a conclusion that _________

a) for V_{i} > 0, V_{0}=-(R_{2}/R_{1})V_{i}

b) for V_{i} > 0, V_{0}=0

c) V_{i} < 0, V_{0}=-(R_{2}/R_{1})V_{i}

d) V_{i} < 0, V_{0}=0

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3. What is the output as a function of the input voltage (for positive values) for the given figure. Assume it’s an ideal op-amp with zero forward drop (D_{i}=0)

a) 0

b) -V_{i}

c) V_{i}

d) 2V_{i}

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4. In a half wave rectifier, the sine wave input is 50sin50t. If the load resistance is of 1K, then average DC power output will be?

a) 3.99V

b) 2.5V

c) 5.97V

d) 6.77V

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_{m}sinωt. BY comparing the given information with this equation, V

_{m}=50. Power=V

_{m}

^{2}/R

_{L}=50*50/1000=2.5V.

5. In a half wave rectifier, the sine wave input is 200sin300t. The average value of output voltage is?

a) 57.876V

b) 67.453V

c) 63.694V

d) 76.987V

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_{m}=200V. Average value is given by, V

_{avg}=V

_{m}/π. So, 200/π=63.694.

6. Efficiency of a half wave rectifier is

a) 50%

b) 60%

c) 40.6%

d) 46%

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_{out}/V

_{in}*100.

7. If peak voltage for a half wave rectifier circuit is 5V and diode cut in voltage is 0.7, then peak inverse voltage on diode will be?

a) 5V

b) 4.9V

c) 4.3V

d) 6.7V

### View Answer

_{m}-V

_{d}=5-0.7=4.3V.

8. Transformer utilisation factor of a half wave rectifier is _________

a) 0.234

b) 0.279

c) 0.287

d) 0.453

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9. If the input frequency of a half wave rectifier is 100Hz, then the ripple frequency will be_________

a) 150Hz

b) 200Hz

c) 100Hz

d) 300Hz

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10. Ripple factor of a half wave rectifier is_________(I_{m} is the peak current and RL is load resistance)

a) 1.414

b) 1.21

c) 1.4

d) 0.48

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## Set 3

1. In the Hall Effect, the directions of electric field and magnetic field are parallel to each other.

The above statement is

a) True

b) False

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2. Which of the following parameters can’t be found with Hall Effect?

a) Polarity

b) Conductivity

c) Carrier concentration

d) Area of the device

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3. In the Hall Effect, the electric field is in x direction and the velocity is in y direction. What is the direction of the magnetic field?

a) X

b) Y

c) Z

d) XY plane

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4. What is the velocity when the electric field is 5V/m and the magnetic field is 5A/m?

a) 1m/s

b) 25m/s

c) 0.2m/s

d) 0.125m/s

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5. Calculate the hall voltage when the Electric Field is 5V/m and height of the semiconductor is 2cm.

a) 10V

b) 1V

c) 0.1V

d) 0.01V

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6. Which of the following formulae doesn’t account for correct expression for J?

a) ρv

b) I/wd

c) σE

d) µH

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7. Calculate the Hall voltage when B=5A/m, I=2A, w=5cm and n=10^{20}.

a) 3.125V

b) 0.3125V

c) 0.02V

d) 0.002V

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^{-2}*10

^{5}*1.6*10

^{-19}) =0.002V.

8. Calculate the Hall Effect coefficient when number of electrons in a semiconductor is 10^{20}.

a) 0.625

b) 0.0625

c) 6.25

d) 62.5

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^{-19}*10

^{20}) =0.0625.

9. What is the conductivity when the Hall Effect coefficient is 5 and mobility is 5cm^{2} /s.

a) 100 S/m

b) 10 S/m

c) 0.0001S/m

d) 0.01 S/m

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^{-4}/5 =0.0001 S/m.

10. In Hall Effect, the electric field applied is perpendicular to both current and magnetic field?

a) True

b) False

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## Set 4

1. For an ideal diode which of the following is true?

a) It allows the passage of current in the forward bias with zero potential drop across the diode

b) It does not allow the flow of current in reverse bias

c) All of the mentioned

d) None of the mentioned

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2. Consider an AC sine wave voltage signal being used to connect a diode and a resistor as shown in the figure. The variation of the voltage across the diode (V_{d}) with respect to time (t) is given by

a)

b)

c)

d) None of the mentioned

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_{d}= V

_{i}– V

_{o}.

3. The figure below shows a circuit for charging a 12-V battery. If V_{s} is a sinusoid with 24-V peak amplitude, the fraction of each cycle during which the diode conducts is

a) One quarter of a cycle

b) One-third of a cycle

c) One half of the cycle

d) Three quarters of a cycle

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_{0}. Hence for a complete cycle the diode does not conducts for 2Θ or 120

_{0}. Hence the diode does not conducts for a third of a cycle.

4. Diodes can be used in the making of

a) Rectifiers

b) LED lamps

c) Logic gates

d) All of the mentioned

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5. For the connections shown below, the equivalent logic gate is

a) OR gate

b) AND gate

c) XOR gate

d) NAND gate

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6. For the connections shown below, the equivalent logic gate is

a) OR gate

b) AND gate

c) XOR gate

d) NAND gate

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7. The figure below shows a circuit for an AC voltmeter. It utilizes a moving-coil meter that gives a full-scale reading when the average current flowing through it is 1 mA. The moving-coil meter has a 50-Ω resistance. The value of R that results in the meter indicating a full-scale reading when the input sine-wave voltage V_{I} is 20 V peak-to-peak is

a) 3.183 kΩ

b) 3.133 kΩ

c) 3.183 Ω

d) 56.183 Ω

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8. The value of I and V for the circuit shown below are

a) 2A and 5V respectively

b) -2A and 5V respectively

c) -2A and -5V respectively

d) 2A and 0V respectively

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9. The units frequently used to measure the forward bias and reverse bias current of a diode are

a) µA and µA respectively

b) µA and mA respectively

c) mA and µA respectively

d) mA and mA respectively

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10. A diode

a) Is the simplest of the semiconductor devices

b) Has a characteristic that closely follows that of a switch

c) Is two terminal device

d) All of the mentioned

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## Set 5

1. What is the minimum number of terminals required in an IC package containing four operational amplifiers (quad op amps)?

a) 12

b) 13

c) 14

d) 15

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2. Which of the following is not a property of an ideal operational amplifier?

a) Zero input impedance

b) Infinite bandwidth

c) Infinite open loop gain

d) Zero common-mode gain or conversely infinite common mode-rejection.

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3. In an ideal op amp the open-loop gain is 10^{3}. The op amp is used in a feedback circuit, and the voltages appearing at two of its three signal terminals are measured as v_{2} = 0V and v_{3} = 2V where it is assumed that v_{1} and v_{2} are input terminals and v_{3} is the output terminal. The value of the differential (v_{d}) and common-mode (v_{cm})signal is

a) V_{d} = 2 mV and v_{cm} = 1 mv

b) V_{d} = 2 mV and v_{cm} = -1 mV

c) V_{d} = 2 mV and v_{cm} = 2mV

d) V_{d} = 2 mV and v_{cm} = -2mV

### View Answer

_{c}= 0.5(V

_{1}+ V

_{2}) and V

_{d = V2 – V1.}

4. Consider the figure given below. Known that v_{o} = 4V and v_{i} = 2V, determine the gain for the op amp assuming that it is ideal except for the fact that it has finite gain

a) 1001

b) 2002

c) 3003

d) 4004

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_{i}= -3.020v A = v

_{o}/ v

_{i}– v

_{r}= -2 / -3.020 -(-3) = 100.

5. Which of the following is not a terminal for the operational amplifier?

a) Inverting terminal

b) Non-inverting terminal

c) Output terminal

d) None of the mentioned

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6. Operational amplifiers are

a) Differential input and single-ended output type amplifier

b) Single-ended input and single-ended output type amplifier

c) Single-ended input and differential output type amplifier

d) Differential input and differential output type amplifier

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7. Express the input voltages v_{1} and v_{2} in terms of differential input (v_{d}) and common-mode input(v_{c}). Given v_{2} > v_{2}.

a) V_{d} = V_{1} – V_{2}, V_{c} = 0.5(V_{1} + V_{2})

b) V_{d} = V_{2} – V_{1}, V_{c} = V_{1} + V_{2}

c) V_{d} = V_{1} – V_{2}, V_{c} = V_{1} + V_{2}

d) V_{d} = V_{2} – V_{1}, V_{c} = 0.5(V_{1} + V_{2})

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8. What is the minimum number of pins for a dual operational amplifier IC package?

a) 4

b) 6

c) 8

d) 10

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9. For an ideal operational amplifier (except for the fact that it has finite gain) one set of the value for the input voltages (v_{2} is the positive terminal v_{1} is the negative terminal) and output voltage (v_{0}) as determined experimentally is v_{1}= 2.01V, v_{2}=2.00V and v_{0}= -0.99V. Experiment was carried with different values of input and output voltages. Which of the following is not possible considering experimental error?

a) v_{1}= 1.99V, v_{2}= 2.00V, v_{0} = 1.00V

b) v_{1}= 1.00V, v_{2}= 1.00V, v_{0} = 0V

c) v_{1}= 1.00V, v_{2}= 1.10V, v_{0} = 10.1V

d) v_{1}= 0.99V, v_{2}= 2.00V, v_{0} = 1.00V

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10. What are the units of slew rate?

a) Second/Volt

b) Volt/second

c) It is a ratio, no units

d) Ohm/second