NESCOM/ NDC / Career 1737 past paper (AM Electronics/Electrical)

AM Electronics/Electrical

1. Carrier frequency 100 kHz and modulated signal frequency 5 kHz what is bandwidth of AM?

a) 100 kHz

b) 105 kHz

c) 5 kHz

d) 10 kHz

Explanation: bandwidth= 2Fm (max) = 2(5 kHz) = 10 kHz

2. What do the content of the stack pointer specify?

a) Address of the top of stack

b) Address of bottom of stack

c) Content of the top of stack

d) content of the bottom of stack

3. An Oscillator produces oscillations due to:

a) positive feedback

b) negative feedback

c) partly positive and partly negative feedback

d) neither positive nor negative feedback

4. In a rectifier, larger the value of shunt capacitor filter;

a) larger the p-p value of ripple voltage

b) larger the peak current in the rectifying diode

c) longer the time that current pulse flows through the diode

d) smaller the dc voltage across the load

 5. A single transistor can be used to build which of the following digital logic gates?

a) AND

b) NAND

c) NOT

d) OR

6. The master slave JK flip-flop is effectively a combination of?

a) A T flip-flop and a D flip-flop

b) An SR flip-flop and a D flip-flop

c) An SR flip-flop and a T flip-flop

d) Two T flip-flops

e) None of the above

7. What is the expected modulation index in case of wide band FM?

a) less than 1

b) 1

1
c) ⁄2

d) more than 1

8. Two important characteristics of CMOS devices are ____________.

a) High noise immunity

b) Low static power consumption

c) High resistivity

d) Both high noise immunity and low static power consumption

9. The main difference between a register and a counter is ___________.

a) A register has no specific sequence of states

b) A counter has no specific sequence of states

c) A register has capability to store one bit of information but counter has n-bit

d) A register counts data

10. Ohm’s law for magnetic circuits is _________

a) F=ϕS

b) F=ϕ/S

c) F=ϕ2S

d) F=ϕ/S2

Explanation: Ohm’s law for magnetic circuits states that the MMF is directly proportional to the
magnetic flux where reluctance is the constant of proportionality.mmf=Flux*Reluctance

11. Which of the following is the fastest switching device?

a) JEFT

b) Triode

c) MOSFET

d) BJT

12. ___________ has tendency to oscillate.

a) Close loop system

b) Open loop system

c) Both (a) and (b)

d) Neither (a) or (b)

13. Resistance of material depends on?

a) Area

b) Length

c) Type of material
d) All

14. A loop antenna is a commonly used for?

a) radar

b) direction finding

c) satellite communication

d) all of the above

15. A better SNR can be obtained in a PCM by,

a) increasing sampling rate above Nyquist rate

b) decreasing the code bits

c) reducing channel bandwidth

d) increasing quantization levels

16. Capacitor bank is used for the improvement of?

Ans: Power Factor

Explanation: Improving power factor means reducing the phase difference between voltage
and current. Since the majority of loads are of inductive nature, they require some amount of
reactive power for them to function. Capacitor banks reduce the phase difference between the
voltage and current.

17. Turn on time of an SCR can be reduced by using a,

a) Triangular pulses

b) Trapezoidal pulses

c) Rectangular pulses of high amplitude and narrow width

d) Rectangular pulses of low amplitude and wide width

18. A modern power semiconductor device that combines the characteristic of BJT and
MOSFET is?

a) IGBT

b) FCT
c) MCT

d) GTO

19. For type 1 system with parabolic input, the steady state error is?

a) Finite constant

b) Infinite

c) zero

20. Relaxation oscillators are used to generate?

a) Sinusoidal wave

b) Triangular wave

c) Saw tooth wave

d) Both B and C (non-sinusoidal)

21. An Op-Amp comparator circuit employs?

a) no feedback

b) +ve feedback

c) -ve feedback

d) Both (b) and (c)

22. RC snubber circuit is used to limit the rate of?

1. Rise of current in SCR

2. Rise of voltage across SCR
3. Conduction period
4. All of the above

23. In PCM system, output S/N increases _____

a) parabolically with bandwidth

b) exponentially with bandwidth (not sure)

c) inversely with bandwidth

d) linearly with bandwidth

 24. An ideal voltmeter has ______equivalent resistance and ideal ammeter has
_____equivalent resistance.

a) Unity, Unity

b) Zero, infinite

c) Infinite, Zero

d) Zero, Zero

25. CPU does not perform the operation?

a) data transfer

b) logic operation

c) arithmetic operation

d) all of the above

26. An RC differentiator acts as a

a) Low pass filter

b) High pass filter

c) Band stop filter

d) Band pass filter

27. The instructions like MOV or ADD are called as ___________.

a) Op code

b) Operators

c) Commands

d) None of above

28. Output of the following program?

#include<stdio.h>
 Int main()

int i=0;

for(i=0; i<5; i++);

cout<<”out =”<<i;

return 0;

a) out = 0 1 2 3 4

b) out = 1 2 3 4 5

c) out = 5

d) out = 4

29. In a frequency counter, what happens at high frequencies when the sampling interval is too
long?

a) The counter works fine

b) The counter undercounts the frequency

c) The measurement is less precise

d) The counter overflows

30. When transistors are used in digital circuits they usually operate in the:

a) active region

b) breakdown region

c) saturation and cutoff regions

d) linear region

31. In a generic microprocessor instruction cycle time is,

Shorter than machine cycle

 Larger than machine cycle time (not sure)

Ten times the machine cycle time

Exactly the same as the machine cycle time

32. _______ is less dependent on the transistor beta

a) Fixed Bias

b) Emitter Bias

c) Voltage Divider

d) Voltage feedback

33. Multi meter typically provides measurements of __________ values.

a) Peak

b) RMS

c) Average

d) Instantaneous

34. Voltage multipliers are circuits best used to produce?

a) low voltage and low current

b) low voltage and high current

c) high voltage and low current

d) high voltage and high current

35. The Process in which A.C is converted into D.C is called?

a) Induction

b) Rectification

c) Dispersion

d) Inversion
 36. Avalanche breakdown occurs at?

a) Knee voltage

b) Breakdown voltage

37. The forward voltage drop across a silicon diode is about?

a) 2.5 V

b) 3V

c) 10 V

d) 0.7 V

1) Which level of system implementation includes the specific function oriented registers,
counters & multiplexers?

(A) Module level

(B) Logical level

(C ) Physical level

(D) All of the above

2) In digital ICs, Schottky transistors are preferred over normal transistors because of
their

(A) Lower Propagation

delay

(B) Higher Propagation delay

(C) Lower Power dissipation

(D) Higher Power dissipation

3) The UJT may be used as

(A) An amplifier
(B) A Saw tooth generator
(C) A
rectifier
(D) None of the above

4) Often a common-collector will be the last stage before the load; the main function(s) of this
stage is to……..
(A) Provide voltage gain

(B) Provide phase inversion

(C) Provide a high-frequency path to improve the frequency response

(D) Buffer the voltage amplifiers from the low-resistance load and provide impedance matching
for maximum power transfer

5) Which one is true?

(A) Series resonant circuit has high impedance

(B) Parallel resonant circuit has low impedance

(C) At frequency greater than resonance frequency, circuit behaves like inductive circuit

(D) Frequency at which XL=XC

6) JFET is;

(A) Voltage controlled current source

(B) Voltage controlled voltage source

(C) Current controlled current source

(D) Current controlled voltage source

7) If gain is +6db and input power is 1mW for an amplifier; what is output power?

(A) 1 mW

(B) 0 mW

(C) 4 mW

(D) None of these

Explanation: Gain in dB=10 log(Po/Pi) So, 6=10 log(Po/1mW)

Po= 3.9mW or 4mW approx.

8) Which motor is used in vacuum cleaner?

(A) Series

(B) Shunt

(C) Cumulative Compound

(D) Differential Compound

Ans: A (Universal/ DC Series Motor is used)

9) What is the average voltage when a rectangular wave's base line voltage is 20 V, its peak-to-
peak voltage is 50 V, and its duty cycle is 20%?

(A) 26 V

(B) 30 V

(C) 40 V

(D) 45 V

10) In which sensor, resistance decrease with increase in temperature;

(A) RTD Resistance Temp Detector

(B) Proximity sensor

(C) Strain guage

(D) RCT

11) In class–A amplifier, the output current flows for

(A) a part of the cycle or the input signal

(B) The full cycle of the input signal

(C) Half the cycle of the input signal

(D) 3/4th of the cycle of the input signal

12) In an amplifier with negative feedback;

(A) Only the gain of the amplifier is affected

(B) Only the gain and bandwidth of the amplifier are affected
(C) Only the input and output impedances are effected

(D) All of the four parameters mentioned above would be affected Gain, bandwidth o/p
impedance, i/p impedance would be affected

13) In a current-series negative feedback amplifier, the input impedance:

(A) Increases

(B) Decreases

(C) Remains unchanged

(D) constant

14) In a voltage-series negative feedback amplifier, the input impedance:

(A) increases

(B) decreases

(C) remains unchanged

(D) constant

15) In two-stage op-amp, what is the purpose of compensation circuitry?

(A) To provide high gain

(B) To lower output resistance & maintain large signal swing

(C) To establish proper operating point for each transistor in its quiescent state

(D) To achieve stable closed-loop performance

16) Which of the following is an undesirable dynamic characteristic of an instrument?

(A) Reproducibility

(B) Dead zone

(C) Time lag

(D) Static error

17) In an amplifier with negative feedback;

(A) Input impedance increases and output impedance decreases

(B) Input impedance decreases and output impedance increases

(C) Both increases

(D) Both remain the same

18) In a circuit Vdc=200V, the effective Ac voltage will be;

(A) 200

(B) 100

(C) 50

(D) 20

(Effective or RMS value is the same as DC value)

19) In terms of circuit components, what does the term pole refer to?

(A) A single RL circuit

(B) A single RC circuit

(C) A Cascaded amplifier

(D) A Summing Amplifier

Laplace of C is 1/s means pole at origin

20) The speed of a DC motor is

(A) Directly proportional to flux per pole

(B) Inversely proportional to flux per pole

(C) Inversely proportional to applied voltage

(D) None of the above

(N=Eb/Φ ∝ V−IaRa/Φ )

21) For proper working of transistors in normal circuit

(A) emitter-base junction is reverse biased and collector-base junction is forward biased
(B) emitter-base junction is forward biased and collector-base junction is reverse biased

(C) emitter-base junction is forward biased and collector-base junction is forward biased

(D) None of them

22) To prevent a DC return between source and load, it is necessary to use ………………

(A) resistor between source and load

(B) inductor between source and load

(C) capacitor between source and load

(D) either (A) or (B)

Capacitor offers infinite impedance to DC

23) If R=20 ohm, XL=40 ohm and XC=15 ohm are connected in series and current is 1A, what
will be the supply voltage?

(A) 220V

(B) 32V

(C) 100V

(D) 40V

Vs=I x sqrt {(R^2 +(XL-XC)^2)}

24) Load impedance ZL=200 ohm, Zi=50ohm then characteristic impedance Zo=

(A) 10000 ohm

(B) 100 ohm

(C) 200 ohm

(D) 4 ohm

Zo= Sqrt (ZLxZi)= 100ohm

25) For a triangular and Saw tooth waveform the RMS voltage or current equals

(A) 0.707times peak value

(B) 0.577 times peak value

(C) 0.577times average value

(D) 0.707times Rms value

26) A figure was given having a diode and a parallel resistor;

Ans: Resistor is used to limit current and diode is used for stopping reverse breakdown voltage

27) Which of the item below is an advantage of a shunt regulator over a series type?

(A) Has an inherent current limiting

(B) Efficient than series regulator because of its component used

(C) A non-regulating device

(D) None of the choices

28) Using electronic devices as switches, what is (are) the general methods of controlling
electrical power?

(A) Static switching

(B) Phase control

(C) Zero voltage switching

(D) All of the above

29) For a constant input voltage to an integrator, why is the voltage across the capacitor linear?

(A) Capacitor diode does not dissipate heat

(B) Capacitor current is constantly changing

(C) Capacitor current is linear

(D) Capacitor current is constant

30) The output of a signal is given. Thermocouple temperature is shown with voltage, find X?

T : 0 5 10
V : -6.66 X -6.82

(A) -2.66

(B) -6.74

31) Signal Sin (Pi^2n) is periodic with

(A) Period of Pi/2

(B) Period of pi^2

(C) Period of 2pi

(D) A periodic

32) For the system in the given figure. The transfer function C(s)/R(s) is

(A) G1 + G2 + 1

(B) G1 G2 + 1

(C) G1 G2 + G2 + 1

(D) G1 G2 + G1 + 1

Transfer function = (G1 + 1) G2 + 1 = G1 G2 + G2 + 1

33) Which of the items below is equivalent to a relaxation oscillator?

(A) Astable multivibrator

(B) Flip-flop

(C) Monostable multivibrator

(D) Bistable multivibrator

34) Which of the following statements is correct?

(A) Actuators and transducers are both examples of sensors.

(B) Sensors and transducers are both examples of actuators.

(C) Sensors and actuators are both examples of transducers

(D) None of them

35) Assuming that the channel is noiseless, if TV channels are 8 kHz wide with the bits/sample
= 3Hz and signaling rate = 16 x 106 samples/second, then what would be the value of data
rate?

(A) 16 Mbps

(B) 24 Mbps

(C) 48 Mbps 16*3=48

(D) 64 Mbps

Explanation: A noiseless channel can carry an arbitrary large amount of information, no matter
how often it is sampled. If each sample is 3 bits, the channel can send 16 x 106 samples/sec * 3
bits = 48 Mbps.

The key word here is “noiseless”. With a normal 8KHz channel, Shannon limit would not allow
this.

36) Theoretically electromagnetic radiation field strength varies in inverse proportion to the
square of the distance, but when atmospheric attenuation effects and the absorption of the
terrain are taken into account the attenuation can be as high as the inverse _______ power of
the distance.

(A) Third

(B) Fourth

(C) Fifth

(D) Sixth

37) Which one is correct?

Ans: Transient Response effects the Speed While Steady-State Response makes accuracy

38) A circuit was given having transistor whose base was grounded, So IB=0A hence,
Vo=Vce=5v Options were: (A) 5V (B) 3.1V(C) 2.5V(D) 0V

1. An RC differentiator acts as a

a) Low-pass filter
 b) High-pass filter

c) Band-pass filter

d) Band-stop filter

2. A heat sink is generally used with a transistor to ___________

a) increase the forward current

b) decrease the forward current

c) compensate for excessive doping

d) prevent excessive temperature rise

3. Megger is used to measure

a) Breakdown voltage of insulation

b) Earth resistance

c) Insulation resistance

d) None of the above

4. Which type of insulator is used on 132 kV transmission lines?

a) Pin type

b) Disc type

c) Shackle type

d) Pin and shackle type

5. The hysteresis cycle for the material of a transformer core is

a) short and wide

b) tall and narrow

c) tall and wide

d) short and narrow

6. At high frequency Transformer core is

 a) Ferrite

b) Soft iron

c) Silicon iron

7. An RC series circuit is connected to 300 volt DC source. The voltage across the
capacitor after one time constant is 189.6

8. Digital signals transmitted on a single conductor (and a ground) must be transmitted

in:

a) slow speed

b) parallel

c) serial

d) analog

9. 2's complement of binary number 0101 is 1011.

Explanation: 1's complement of 0101 is 1010 and 2's complement is 1010+1 = 1011

10. How a triangular wave generator is derived from square wave generator?

a) Connect oscillator at the output

b) Connect Voltage follower at the output

c) Connect differential at the output

d) Connect integrator at the output

11. A silicon semiconductor diode when subjected to ohmmeter testing gives low resistance
in both the directions. Which of the following is the correct inference to be drawn?

a) Diode is faulty

b) Power failure to the Ohmmeter

c) Diode is short-circuited

d) Diode is open circuited

Explanation: A proper diode gives a low resistance reading along one direction and
high resistance reading along the other. Hence, if diode gives low resistance
 readings in both the directions, then the diode must be short-circuited. It’s noteworthy
that a faulty diode gives a high resistance reading along both the paths.

12. In the flux control method for controlling the speed of D.C. shunt motor, the speed
control is not possible

a) Below normal rated speed

b) Above normal rated speed

c) Both (a) and (b)

d) None of these

13. A relay is ……….. Switch

a) A mechanical

b) An electronic

c) An electromechanical

d) None of the above

14. An integrating circuit is a simple RC series circuit with output taken across ………

a) Both R and C

b) R

c) C

d) None of the above

15. The inputs of a NAND gate are connected together. The resulting circuit is ………….

a) OR gate

b) AND gate

c) NOT gate

d) None of the above

16. An SCR can exercise control over ………. of a.c. supply

a) Positive half-cycles only

 b) Negative half-cycles only

c) Both positive and negative half-cycles

d) Positive or negative half-cycles

17. With zero volts on both inputs, an OP-amp ideally should have an output ………..

a) equal to the positive supply voltage

b) equal to the negative supply voltage

c) equal to zero

d) equal to CMRR

18. ………….. multivibrator is a square wave oscillator.

a) Monostable

b) Astable

c) Bistable

d) none of the above

19. The deflection sensitivity of a CRT depends inversely on the

a) Distance between screen and defecting plates

b) Length of the vertical deflecting plates

c) Separation between Y- plates

d) Defecting voltage

20. Number of magnetic circuits in a four pole DC machine is

a) One

b) Two

c) Four

d) eight

21. If a copper wire is stretched to make it 0.1% longer. What is the percentage change in
its resistance?
 a) 0.2

b) 0.4

c) 1

d) 2

22. A resistance R1 is connected with a DC generator and dissipates power if R2 is inserted

in Series with it, power dissipated across R1

a) Remain same

b) Increases

c) Decreases

23. Power factor of induction motor is lagging during

a) Starting

b) Operation

c) Operation and starting

24. In open loop control system

a) Output is independent of control input

b) input is independent of system parameters

c) system parameters have effect on the control output

d) all of the above

25. When bandwidth is the major consideration a narrow and wide band FM can be
approximated to?

a) DSB-SC

b) SSB

c) VSB

d) AM
Explanation: For narrow and wide bands frequency modulation, modulation index is
respectively smaller and greater than 1. When bandwidth is considered it can be approximated
to AM

26. A current flows in a conductor from east to west. The direction of the magnetic field at a
point above the conductor is: towards north

27. Power factor of a transformer

a) Leading

b) Lagging

c) Depends on load

d) None

28. The steady state stability of the power system can be improved by:

a) Increasing the number of parallel lines between the transmission points

b) Connecting capacitors in series with the line
c) Reducing the excitation of the machines
d) Both a and b

29. Which component of Hartley oscillator is used in feedback system?

a) Inductor

b) Resistor

c) Capacitor

d) Transistor

Explanation: The feedback used in Hartley oscillator is Voltage series feedback. Center
tapped inductors are used in Hartley oscillator to ensure feedback. These are often in
parallel to a variable capacitor, and feedback is sent into the base of the transistor.

30. The voltage regulation of an alternator with a power factor of 0.8 lagging is _____ at
unity power factor

a) greater than b) the same as c) smaller than d) 100%

31. An over-excited synchronous motor running in parallel with induction motors can be
used in improve the power factor of

a) supply line

b) Transformer
 c) Generators

d) all of the above

32. The position and velocity errors of a type-2 system are

a) constant, constant

b) constant, infinity

c) zero, constant

d) zero, zero

33. Spring constant in force-voltage analogy is analogous to

a) Capacitance

b) reciprocal of capacitance

c) current

d) Resistance

35. Which motor has the best speed regulation?

a) Series (poor speed regulation)

b) Shunt

c) Commutatively compounded

d) Differentially compounded (negative speed regulation)

36. Output of SCR in Cutoff Region

a) 0 b) Vcc, Ic=0A c) Vcc/2 d) Vcc/3

39. Which of the following can be the output of PLC?

1. Relay coils
2. Solenoids
3. Indicators
4. Motors
5. Lamps
6. Alarms
a) Only (1), (2), (3) and (4)
b) Only (3), (4), (5) and (6)
c) Only (1), (2), (3) and (5)
d) All the (1), (2), (3), (4), (5), and (6)