# SSC Scientific Assistant (IMD) Exam : Held on 22 Nov 2017 Shift-1 (ELECTRONICS)

## SSC Scientific Assistant (IMD) Exam : Held on 22 Nov 2017 Shift-1

## (ELECTRONICS)

**QID : 501 - A resistance has colour-coded value of 500 ohms with ±15 %
tolerance. What is the range (in ohms) in which actual resistance of this
resistor can vary?**

1) 425 to 575

2) 470 to 530

3) 485 to 515

4) 350 to 650

**Correct Answer: 425 to 575**

**QID : 502 - What will be the current carrying capacity of a wire when its
radius is doubled?**

1) Current carrying capacity becomes one-fourth of the original value.

2) Current carrying capacity becomes one-sixth of the original value.

3) Current carrying capacity remains same.

4) Current carrying capacity becomes four times of the original value.

**Correct Answer: Current carrying capacity becomes
four times of the original value.**

**QID : 503 - Which of the following are active components?**

**I. Resistor
II. Capacitor
III. Independent voltage source
IV. Dependent current source**

1) I only

2) I and III only

3) II and III only

4) III and IV only

**Correct Answer: III and IV only**

**QID : 504 - When a sample of silicon and germanium material, having same
impurity concentration, is kept at 30 degree Celsius then,______________.**

1) both will have equal value of resistivity.

2) both will have equal positive resistivity.

3) both will have equal negative resistivity.

4) resistivity of germanium will be lower than that of silicon.

**Correct Answer: resistivity of germanium will be
lower than that of silicon.**

**QID : 505 - Which of the following is the SI unit of Inductance?**

1) Tesla

2) Henry

3) Farad

4) Ohms

**Correct Answer: Henry**

**QID : 506 - What does the line (|) in the symbol of a diode signifies?**

1) n-type material (anode)

2) n-type material (cathode)

3) p-type material (anode)

4) p-type material (cathode)

**Correct Answer: n-type material (cathode)**

**QID : 507 - A 9.6 V Zener diode shows its nominal voltage when a test
current of 30 mA is passed through it. The incremental resistance at this
particular value of current is found to be 6 ohms. Calculate the breakdown
voltage (in Volts) of Zener diode model**.

1) 9.364

2) 9.465

3) 9.582

4) 9.679

**Correct Answer: 9.582**

**QID : 508 - Name the circuit which removes the negative part of the
waveform.**

1) Limiter

2) Negative clamper

3) Positive clamper

4) Negative clipper

**Correct Answer: Negative clipper**

**QID : 509 - What is the ripple frequency (in Hz) of a full wave center-tap
rectifier when it is supplied by a supply of frequency 110 Hz?**

1) 50

2) 55

3) 60

4) 220

**Correct Answer: 220**

**QID : 510 - A 16 V DC supply is used to power an LED having rating 1.6 V
and 25 mA. What is the minimum value of series resistance (in ohms) required for
safe operation of the LED?**

1) 576

2) 584

3) 625

4) 656

**Correct Answer: 576**

**QID : 511 - For an NPN-transistor, the value of alpha (α) is 0.99.
Calculate the value of beta (β).**

1) 0.99

2) 49

3) 99

4) 100

**Correct Answer: 99**

**QID : 512 - What is the pinch off voltage (in Volts) of an n-channel
enhancement mode MOSFET having threshold voltage of 0.5 V when it is subjected
to a gate voltage of 5 V?**

1) 2.5

2) 3

3) 3.5

4) 4.5

**Correct Answer: 4.5**

**QID : 513 - In which of the following semiconductor devices, the path for
carriers (electrons and holes) is not present initially but is developed during
the operation?**

1) BJT

2) D-MOSFET

3) E-MOSFET

4) JFET

**Correct Answer: E-MOSFET**

**QID : 514 - The maximum power dissipation of a BJT is calculated as 0.4 W
at 25 degree Celsius having derating factor of 0.0025 W/degree Celsius. What
will be the maximum power dissipation (in W) at 50 degree Celsius?**

1) 0.3375

2) 0.3975

3) 0.4025

4) 0.4625

**Correct Answer: 0.3375**

**QID : 515 - Which among the following electronic devices contains silicon
dioxide layer?**

1) JFET

2) MOSFET

3) NPN transistor

4) PNP transistor

**Correct Answer: MOSFET**

**QID : 516 - Which of the following BJT circuit has a voltage gain
approximately equal to one?**

1) Common base

2) Common emitter

3) Emitter follower

4) Collector follower

**Correct Answer: Emitter follower**

**QID : 517 - Which of the following is correct about gain of a cascade
amplifier?**

1) Total gain is difference of individual gains.

2) Total gain is product of voltage and current gains.

3) Total gain is ratio of individual gains.

4) Total gain is sum of individual gains.

**Correct Answer: Total gain is sum of individual
gains.**

**QID : 518 - What is the reason for the use of RC coupling in low-level
audio amplifiers?**

1) It has better low frequency response than other amplifiers.

2) It does not need any adjustment.

3) The output is in phase with input signal.

4) Requires less voltage for operation.

**Correct Answer: It does not need any adjustment.**

**QID : 519 - What is the percentage load regulation if a voltage regulation
having no-load output of 20 V, has a full-load output of 18.5 V?**

1) 0.044

2) 0.052

3) 0.074

4) 0.081

**Correct Answer: 0.081**

**QID : 520 - What is the overall gain of the system if the output of the
amplifier which has a gain of 10 is negatively feedback to input through another
amplifier having gain of 5?**

1) 0.098

2) 0.196

3) 0.294

4) 0.492

**Correct Answer: 0.196**

**QID : 521 - Which of the following theorem explains the statement – ‘If
the positions of voltage source and ammeter are interchanged with each other in
a circuit, the reading of ammeter remains same and the circuit contains only 1
energy source.’?**

1) Maximum power transfer theorem

2) Norton theorem

3) Reciprocity theorem

4) Superposition theorem

**Correct Answer: Reciprocity theorem**

**QID : 522 - **

1) 3.05

2) 3.15

3) 3.25

4) 3.35

**Correct Answer: 3.35**

**QID : 523 - What will be the output (in Volts) of a voltage divider having
resistance of 50 ohms and 150 ohms and a 20 V source when output is taken across
150 ohms resistor?**

1) 15

2) 18

3) 20

4) 22

**Correct Answer: 15**

**QID : 524 - Four resistors each of 5 kilo-ohms are connected in series
with each other along with a 25 V voltage source. If a 20 kilo-ohms resistor is
connected in parallel across one of the 5 kilo-ohms resistance, then what will
be the value of total current (in mA) flowing in the circuit?**

1) 0.654

2) 0.685

3) 0.893

4) 1.316

**Correct Answer: 1.316**

**QID : 525 - **

1) 2 A current source with 32 ohms resistor in parallel

2) 4 A current source with 16 ohms resistor in parallel

3) 2 A current source with 32 ohms resistor in series

4) 4 A current source with 16 ohms resistor in series

**Correct Answer: 4 A current source with 16 ohms
resistor in parallel**

**QID : 526 - What is the value of current (in A) at a point where 54 C of
charge passes in 16 seconds?**

1) 2.275

2) 3

3) 3.375

4) 4

**Correct Answer: 3.375**

**QID : 527 - What is the capacitance (in µF) of a parallel plate capacitor
if it stores 15 mC of charge when connected across 18 V supply?**

1) 8.33

2) 16.66

3) 83.33

4) 833.33

**Correct Answer: 833.33**

**QID : 528 - Which of the following uses wiper sliding contact?**

1) Diode

2) LED

3) Potentiometer

4) Thermistor

**Correct Answer: Potentiometer**

**QID : 529 - What is the voltage (in Volts) across a 5 H inductor when a
current of (15 t + 30) A is flowing through the circuit?**

1) 55

2) 60

3) 65

4) 75

**Correct Answer: 75**

**QID : 530 - What is the admittance (in mho) of a circuit in which 5 ohms
and 15 ohms series resistors are connected in series with an inductor having
inductive reactance of 25 ohms?**

1) 0.03125

2) 0.625

3) 1.25

4) 12.5

**Correct Answer: 0.03125**

**QID : 531 - What is the value of susceptance (in Siemens) of a circuit if
the same circuit has reactance and resistance of 8 ohms and 6 ohms respectively?**

1) -0.08

2) -0.04

3) 0

4) 0.04

**Correct Answer: -0.08**

**QID : 532 - What is the value of conductance (in Siemens) of a circuit if
the same circuit has reactance and resistance of 8 ohms and 6 ohms respectively?**

1) -0.06

2) -0.03

3) 0

4) 0.06

**Correct Answer: 0.06**

**QID : 533 - **

1) 20

2) 21

3) 25

4) 29

**Correct Answer: 29**

**QID : 534 - What is the quality factor of a series RLC circuit having
resistance, inductance and capacitance of 20 ohms, 1 mH and 0.01 mF,
respectively?**

1) 0.5

2) 0.75

3) 1

4) 1.25

**Correct Answer: 0.5**

**QID : 535 - What is the quality factor of a parallel RLC circuit having
resistance, inductance and capacitance of 20 ohms, 1 mH and 0.01 mF
respectively?**

1) 0.5

2) 1

3) 1.5

4) 2

**Correct Answer: 2**

**QID : 536 - What is the bandwidth (in Hz) of a parallel RLC circuit having
resistance, inductance and capacitance of 20 ohms, 1 mH and 0.01 mF respectively
with a resonant frequency of 60 Hz?**

1) 20

2) 30

3) 40

4) 50

**Correct Answer: 30**

**QID : 537 - A delta connected network consumes 6.4 kW at 0.8 lagging power
factor when connected to a 400 V, 50 Hz source. What is the approximate per
phase impedance (in Ohms) of the delta network?**

1) 50

2) 55

3) 60

4) 6

**Correct Answer: 60**

**QID : 538 - A star connected load has phase current of 10 A and equal
phase impedance of (4 + j3) ohms. Calculate the value of line voltage (in Volts)
supplying the star connected load.**

1) 64.4

2) 86.6

3) 108.8

4) 131

**Correct Answer: 86.6**

**QID : 539 - If a delta network has three equal resistances each of 153
ohms, then, calculate the equivalent star network resistance (in Ohms) in each
phase.**

1) 51

2) 102

3) 153

4) 306

**Correct Answer: 102**

**QID : 540 - What is the value of separation between the voltages in a
balanced three-phase system?**

1) 30°

2) 45°

3) 60°

4) 120°

**Correct Answer: 120°**

**QID : 541 - What is the 16's compliment of hexadecimal number 5EF?**

1) 9A0

2) 921

3) AF1

4) A11

**Correct Answer: A11**

**QID : 542 - How many inputs are required to form truth table of the SOP
expression ABD + BD + A + AD?**

1) 1

2) 2

3) 3

4) 4

**Correct Answer: 3**

**QID : 543 - What is minimum number of logic gates required to implement
the Boolean expression AB + A (A + B) + B (A + B) without simplifying it?**

1) 1

2) 2

3) 3

4) 5

**Correct Answer: 5**

**QID : 544 - What is the resolution (in Volts) of a 4-bit ADC having
reference voltage of 12 V?**

1) 0.5

2) 0.75

3) 1

4) 1.25

**Correct Answer: 0.75**

**QID : 545 - What will be the voltage reading of an ADC having resolution
of 1023 and reference voltage of 5 V while measuring a voltage of 4.3 V?**

1) 6602) 770

3) 880

4) 990

**Correct Answer: 880**

**QID : 546 - What is the output frequency (in kHz) of a frequency division
circuit having 10 flip-flops with an input clock frequency of 40.96 MHz?**

1) 10

2) 20

3) 30

4) 40

**Correct Answer: 40**

**QID : 547 - What is the minimum number of flip-flops required to produce
modulo-256 counter?**

1) 1

2) 2

3) 4

4) 8

**Correct Answer: 8**

**QID : 548 - What will be the count in a MOD-8 ripple counter which is
holding the binary count 101 after 25 clock pulses?**

1) 100

2) 101

3) 110

4) 010

**Correct Answer: 110**

**QID : 549 - The group of bits 10101 is serially shifted (right-most bit
first) into a 5-bit parallel output shift register with an initial state of
01001. What is the value contained in the register after 2 clock pulses?**

1) {01010}

2) {01011}

3) {10001}

4) {10011}

**Correct Answer: {01010}**

**QID : 550 - If the input resistor of 50 kilo-ohms of a binary weighted DAC
is connected to a 6 V supply, then, what will be the current flowing through the
resistor?**

1) 60 µA

2) 120 µA

3) 6 mA

4) 60 mA

**Correct Answer: 120 µA**

## Study Kit for SSC Scientific Assistant (IMD) Examination

**QID : 551 - What is the expression for minimum transmission bandwidth of a
PAM-TDM channel?**

1)

2)

3)

4)

**Correct Answer: 2**

**QID : 552 - Crosstalk is defined as _______________.**

1) Interference between adjacent TDM channels

2) Interference between adjacent PCM channels

3) Interference between adjacent PAM channels

4) Interference between adjacent AM channels

**Correct Answer: Interference between adjacent TDM
channels**

**QID : 553 - The number of simultaneous conversations that can be
transmitted using FDM depends on the total ______________ available.**

1) Frequency components

2) Phase

3) Bandwidth

4) Both frequency and bandwidth

**Correct Answer: Bandwidth**

**QID : 554 - Which of the following modulation technique is rare in digital
communication?**

1) FSK

2) PSK

3) ASK

4) BPSK

**Correct Answer: ASK**

**QID : 555 - Which non-coherent binary modulation technique uses two
transmitted frequencies in noisy channel?**

1) FSK

2) BPSK

3) QPSK

4) ASK

**Correct Answer: FSK**

**QID : 556 - Which modulation technique is preferred over amplitude shift
keying (ASK)?**

1) FSK

2) BPSK

3) MSK

4) FSK and PSK

**Correct Answer: FSK and PSK**

**QID : 557 - What is the minimum bandwidth of a BPSK signal?**

1)

2)

3)

4)

**Correct Answer: 2**

**QID : 558 - On which factor, the probability of error of ASK modulation
technique depends?**

1) Amplitude

2) Signal energy

3) Bit rate

4) Error signal

**Correct Answer: Signal energy**

**QID : 559 - What is the range of losses caused due to hydrogen absorption
mechanisms?**

1) 0 dB/km to 5 dB/km

2) 10 dB/km to 15 dB/km

3) 20 dB/km to 25 dB/km

4) 25 dB/km to 50 dB/km

**Correct Answer: 25 dB/km to 50 dB/km**

**QID : 560 - Which among the following is/are correct with respect to PCM?**

**1. PCM system has better noise immunity as compared to other systems.
2. PCM is unaffected by width of the pulses.
3. PCM is affected by the position of the pulses.**

1) 1 only

2) 1 and 2 only

3) 1 and 3 only

4) 2 and 3 only

**Correct Answer: 1 and 2 only**

**QID : 561 - A binary PCM system transmits a TV signal having a bandwidth
of 3.2 MHz with 512 number of quantization levels. Calculate the code word
length and transmission bandwidth of given PCM system respectively.**

1) 5 bits, 35 MHz

2) 6 bits, 27.5 MHz

3) 9 bits, 28.8 MHz

4) 10 bits, 38.7 MHz

**Correct Answer: 9 bits, 28.8 MHz**

**QID : 562 - In delta modulation, Granular or Idle noise occurs when step
size is ___________ compared to small variations in the input signal.**

1) Too large

2) Large

3) Small

4) Slightly less

**Correct Answer: Too large**

**QID : 563 - The spectral efficiencies for all the line codes can be easily
evaluated from their ______________.**

1) Probability of error

2) Bandwidth

3) Power spectral density

4) Both Bandwidth and Power spectral density

**Correct Answer: Power spectral density**

**QID : 564 - Determine the number of bits of quantization noise that are
needed to achieve a signal to noise ratio of at least 40 dB?**

1) 5 bits

2) 6 bits

3) 7 bits

4) 8 bits

**Correct Answer: 7 bits**

**QID : 565 - Calculate the bandwidth of a PCM system, if the amplitude
levels are transmitted in a 7 unit code and sampling is done at the rate of 10
kHz.**

1) 25 kHz

2) 30 kHz

3) 35 kHz

4) 40 kHz

**Correct Answer: 35 kHz**

**QID : 566 - Which of the following technique is not suitable for automatic
satellite tracking?**

1) Step-track technique

2) Conical scanning

3) Lobe switching

4) Mono pulse switching

**Correct Answer: Step-track technique**

**QID : 567 - NASA launched three satellites, named Biosatellite (1, 2 & 3)
between _______ and ________.**

1) 1965, 1969

2) 1966, 1968

3) 1956, 1958

4) 1966, 1969

**Correct Answer: 1966, 1969**

**QID : 568 - Which of the following contracted the launch of AsiaSat 2
satellite?**

1) Asia Satellite Telecommunications Company (ASTC)

2) Japan Satellite System (JSAT)

3) China Great Wall Industry Corporation

4) Singapore Satellite Commission

**Correct Answer: China Great Wall Industry
Corporation**

**QID : 569 - The point on the satellite orbits that is close to the earth
is ____________.**

1) Apogee

2) Perigee

3) Prograde

4) Zenith

**Correct Answer: Perigee**

**QID : 570 - Which of the following device is used for the conversion of
electrons to photons or photons to electrons?**

1) Antenna

2) Electron gun

3) Photon amplifier

4) Microwave tube

**Correct Answer: Antenna**

**QID : 571 - What is the total number of radiation pattern required to
specify the characteristics of an antenna?**

1) One

2) Two

3) Three

4) Five

**Correct Answer: Three**

**QID : 572 - **

1) 10 dB

2) 11 dB

3) 12 dB

4) 13 dB

**Correct Answer: 13 dB**

**QID : 573 - What is the directivity of an antenna that radiates power over
half a sphere?**

1) One

2) Two

3) Three

4) Four

**Correct Answer: Two**

**QID : 574 - Determine the efficiency of an antenna (per cent), if the
power at input side is 200 mW and the radiated power is to be 80 mW.**

1) 0.5

2) 0.4

3) 0.355

4) 0.45

**Correct Answer: 0.4**

**QID : 575 - In ________________ the media of transmission is a pair of
conductors called transmission line.**

1) Radio communication

2) Wireless communication

3) Line communication

4) Wired communication

**Correct Answer: Line communication**

**QID : 576 - Which among the following is/are correct for the need of
modulation?**

**1. Multiplexing
2. Narrow banding
3. Practicability of antennas**

1) 1 only

2) 2 and 3 only

3) 1 and 3 only

4) 1, 2 and 3

**Correct Answer: 1, 2 and 3**

**QID : 577 - A __________________ requires a non-linear element and a low
pass filter for extracting the desired message signal.**

1) Envelope detector

2) Square law detector

3) Demodulator

4) Frequency limiter

**Correct Answer: Square law detector**

**QID : 578 - A compromise between the DSB-SC modulation and the SSB
modulation is known as ____________.**

1) VSB modulation

2) Conventional AM-DSB modulation

3) Angle modulation

4) Phase modulation

**Correct Answer: VSB modulation**

**QID : 579 - Which of the following factor measures the performance of both
Analog and digital communication system?**

1) Input signal-to-noise power ratio

2) Output signal-to-noise power ratio

3) Probability of error

4) Both probability of error and output signal to noise power ratio

**Correct Answer: Both probability of error and output
signal to noise power ratio**

**QID : 580 - The demodulator filter which is the inverse of the modulator
filter is called the _____________.**

1) Pre-emphasis filter (HPF)

2) De-emphasis filter (LPF)

3) Band pass filter

4) Demodulation filter

**Correct Answer: De-emphasis filter (LPF)**

**QID : 581 - Which of the following shift keying involved the most complex
signal detection process?**

1) ASK

2) FSK

3) PSK

4) Both ASK and FSK

**Correct Answer: PSK**

**QID : 582 - Delta modulation transmits ___________ per sample.**

1) one bit

2) two bytes

3) three bytes

4) four bytes

**Correct Answer: three bytes**

**QID : 583 - What is the meaning of scrambling of data?**

1) Exchanging of data

2) Removing long strings of 1's and 0's

3) Transmission of digital data

4) Transmission of Analog data

**Correct Answer: Removing long strings of 1's and 0's**

**QID : 584 - Which of the following is the correct sequence of subsystems
in an FM receiver?**

1) Mixer, RF amplifier, Limiter, IF amplifier, Discriminator, Audio amplifier

2) RF amplifier, Mixer, Limiter, IF amplifier, Discriminator, Audio amplifier

3) Mixer, RF amplifier, IF amplifier, Limiter, Discriminator, Audio amplifier

4) Mixer, RF amplifier, Limiter, Discriminator, IF amplifier, Audio amplifier

**Correct Answer: RF amplifier, Mixer, Limiter, IF
amplifier, Discriminator, Audio amplifier**

**QID : 585 - In frequency modulation, the frequency deviation is
_________________ to the modulating signal frequency.**

1) directly proportional

2) inversely proportional

3) independent

4) inversely proportional to the square root of modulating signal

**Correct Answer: directly proportional**

**QID : 586 - Determine the value of power in the carrier of modulation
index of 0.5, if the radiated power of AM transmitter is 10 kW.**

1) 13 kW

2) 13.33 kW

3) 14.45 kW

4) 15 kW

**Correct Answer: 14.45 kW**

**QID : 587 - Which of the following noise affects the performance of
communication system at higher frequencies?**

1) Shot noise

2) Flicker noise

3) Random noise

4) Transit-time noise

**Correct Answer: Transit-time noise**

**QID : 588 - To get FM by using PM, we first ____________ the baseband
signal and then apply to the phase modulation.**

1) Differentiate

2) Integrate

3) Multiply

4) Limit

**Correct Answer: Integrate**

**QID : 589 - The artificial boosting of higher modulating frequencies is
called ______________.**

1) Pre-emphasis

2) De-emphasis

3) Frequency limiting

4) Amplitude limiting

**Correct Answer: Pre-emphasis**

**QID : 590 - **

1) 67.5 kHz, 83.5 %

2) 62.5 kHz, 83.3%

3) 60.25 kHz, 90.4 %

4) 66.7 kHz, 85.3%

**Correct Answer: 62.5 kHz, 83.3%**

**QID : 591 - Which of the following propagation is also termed as
point-to-point propagation?**

1) Ground wave propagation

2) Space wave propagation

3) Sky wave propagation

4) Troposphere scatter propagation

**Correct Answer: Sky wave propagation**

**QID : 592 - Which of the following is the line of sight (LOS) propagation?**

1) Forward scatter propagation

2) Backward scatter propagation

3) Space wave propagation

4) Duct propagation

**Correct Answer: Space wave propagation**

**QID : 593 - **

1) 12.727 MHz

2) 15.525 MHz

3) 17.772 MHz

4) 14.386 MHz

**Correct Answer: 12.727 MHz**

**QID : 594 - The phenomenon of splitting of wave into two different
components by the earth's magnetic field is termed as ___________________.**

1) Magnet splitting

2) Magnet ionic splitting

3) Magneto ionic splitting

4) Magneto splitting

**Correct Answer: Magneto ionic splitting**

**QID : 595 - Which of the following Ionospheric abnormalities is also
termed as Mongel-Dellinger Effect?**

1) Ionospheric storms

2) Sun spot cycle

3) Fadings

4) Sudden ionospheric disturbances (SID)

**Correct Answer: Sudden ionospheric disturbances
(SID)**

**QID : 596 - Which type of signals is propagating primarily by ground waves
during the day and by sky waves at night?**

1) FM broadcast signals

2) AM broadcast signals

3) Sinusoidal signals

4) Both AM and FM signals

**Correct Answer: AM broadcast signals**

**QID : 597 - The carrier amplitude after AM varies between 5 volts and 2
volts. Determine the depth of modulation.**

1) 0.45

2) 0.425

3) 0.443

4) 0.5

**Correct Answer: 0.425**

**QID : 598 - Which type of modulation produces the best type of amplitude
modulation (AM)?**

1) High level modulation

2) Low level modulation

3) Mid level modulation

4) Both High level modulation and Low level modulation

**Correct Answer: High level modulation**

**QID : 599 - What are the frequency components in an AM wave?**

1)

2)

3)

4)

**Correct Answer: 4**

**QID : 600 - Calculate the peak amplitude of the carrier of an antenna of
(50 + j 0) ohms load if given AM broadcast station transmits a total power of 50
kW and its carrier power is 40 kW.**

1) 53 kV

2) 63.24 kV

3) 64 kV

4) 65 kV

**Correct Answer: 63.24 kV**