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Latest NPCIL Stipendiary Trainee Instrument Mechanic Exam Question (Objective Questions), MCQ in English

Subjects : Instrument & Electronics Mechanic

Question Bank NPCIL Stipendiary Trainee Instrument Mechanic (Advanced Test) Exam - English
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Instrument & Electronics Mechanic

Question 1Single Answer
What is the primary advantage of frequency modulation (FM) over amplitude modulation (AM)?
  1. A
    Simpler transmitter
  2. B
    Less bandwidth requirement
  3. C
    Better noise immunity
  4. D
    Lower cost
Question 2Single Answer
In amplitude modulation, which of the following varies with the modulating signal?
  1. A
    Frequency
  2. B
    Phase
  3. C
    Amplitude
  4. D
    Wavelength
Question 3Single Answer
The bandwidth of an AM signal is:
  1. A
    Equal to the carrier frequency
  2. B
    Twice the modulating frequency
  3. C
    Same as the modulating frequency
  4. D
    Half the carrier frequency
Question 4Single Answer
Which device is commonly used for demodulating AM signals?
  1. A
    Diode detector
  2. B
    Mixer
  3. C
    Amplifier
  4. D
    Oscillator
Question 5Single Answer
What is the function of a modulator in a communication system?
  1. A
    Amplify signal
  2. B
    Store data
  3. C
    Combine signal and carrier
  4. D
    Convert analog to digital
Question 6Single Answer
In frequency modulation, the:
  1. A
    Carrier amplitude varies
  2. B
    Carrier frequency varies
  3. C
    Carrier phase varies
  4. D
    Carrier bandwidth varies
Question 7Single Answer
What is a key disadvantage of AM transmission?
  1. A
    High efficiency
  2. B
    Poor sound quality
  3. C
    Complex receivers
  4. D
    High bandwidth usage
Question 8Single Answer
The term "modulation index" in AM refers to:
  1. A
    Carrier frequency to signal frequency ratio
  2. B
    Signal frequency to carrier amplitude ratio
  3. C
    Ratio of signal amplitude to carrier amplitude
  4. D
    Power of carrier wave
Question 9Single Answer
A superheterodyne receiver uses a:
  1. A
    Frequency multiplier
  2. B
    Crystal oscillator
  3. C
    Intermediate frequency
  4. D
    Class C amplifier
Question 10Single Answer
Which of the following is used to reduce noise in FM systems?
  1. A
    Phase-locked loop
  2. B
    Diode
  3. C
    Mixer
  4. D
    Demultiplexer
Question 11Single Answer
A thyristor can be turned off by:
  1. A
    Increasing the gate voltage
  2. B
    Reversing the polarity
  3. C
    Bringing current below holding current
  4. D
    Applying a negative pulse at gate
Question 12Single Answer
What type of device is a TRIAC?
  1. A
    Two-terminal
  2. B
    Three-terminal, bi-directional
  3. C
    Four-terminal, uni-directional
  4. D
    Three-terminal, uni-directional
Question 13Single Answer
Which device is used to convert AC to DC?
  1. A
    Inverter
  2. B
    Rectifier
  3. C
    Cycloconverter
  4. D
    Amplifier
Question 14Single Answer
A chopper is used for:
  1. A
    Voltage multiplication
  2. B
    Voltage inversion
  3. C
    DC to DC conversion
  4. D
    AC to DC conversion
Question 15Single Answer
Which motor is commonly used in variable speed drives?
  1. A
    DC shunt motor
  2. B
    Induction motor
  3. C
    Synchronous motor
  4. D
    Stepper motor
Question 16Single Answer
In a full-wave rectifier, the ripple frequency is:
  1. A
    Equal to supply frequency
  2. B
    Half of supply frequency
  3. C
    Twice the supply frequency
  4. D
    Zero
Question 17Single Answer
The advantage of IGBT over BJT is:
  1. A
    Higher switching speed
  2. B
    Lower cost
  3. C
    Simple gate drive
  4. D
    High voltage rating
Question 18Single Answer
What does PWM stand for in drives?
  1. A
    Pulse Width Modulation
  2. B
    Power Width Motor
  3. C
    Power Watt Modulator
  4. D
    Pulse Watt Mode
Question 19Single Answer
Which device is used in SMPS to convert power efficiently?
  1. A
    Diode
  2. B
    SCR
  3. C
    MOSFET
  4. D
    Zener diode
Question 20Single Answer
Which of the following can work as both rectifier and inverter?
  1. A
    BJT
  2. B
    IGBT
  3. C
    Thyristor
  4. D
    Cycloconverter
Question 21Single Answer
What is the purpose of a carrier signal in modulation?
  1. A
    To transmit data over short distances
  2. B
    To reduce the size of the message
  3. C
    To allow transmission over long distances
  4. D
    To amplify the signal
Question 22Single Answer
The main disadvantage of frequency modulation is:
  1. A
    High noise sensitivity
  2. B
    Complex circuitry
  3. C
    Poor sound quality
  4. D
    Low fidelity
Question 23Single Answer
In FM, the deviation ratio is defined as:
  1. A
    Maximum deviation / modulating frequency
  2. B
    Carrier frequency / signal frequency
  3. C
    Signal power / carrier power
  4. D
    Modulation index / frequency
Question 24Single Answer
Which type of modulation is used for TV video signals?
  1. A
    AM
  2. B
    FM
  3. C
    PM
  4. D
    PCM
Question 25Single Answer
The process of extracting the original signal from a modulated wave is known as:
  1. A
    Multiplexing
  2. B
    Demodulation
  3. C
    Rectification
  4. D
    Modulation
Question 26Single Answer
In AM, the total power is the sum of:
  1. A
    Carrier and signal powers
  2. B
    Sidebands and carrier power
  3. C
    Baseband and bandwidth
  4. D
    Carrier and noise power
Question 27Single Answer
The FM wave has:
  1. A
    Constant amplitude
  2. B
    Varying amplitude
  3. C
    Constant frequency
  4. D
    Constant phase
Question 28Single Answer
Modulation index in FM depends on:
  1. A
    Carrier frequency
  2. B
    Frequency deviation and modulating frequency
  3. C
    Carrier amplitude
  4. D
    Transmission power
Question 29Single Answer
Which device is used for frequency demodulation?
  1. A
    Envelope detector
  2. B
    PLL circuit
  3. C
    Bridge rectifier
  4. D
    Filter circuit
Question 30Single Answer
In a communication system, noise mainly affects:
  1. A
    Modulation
  2. B
    Transmission
  3. C
    Reception
  4. D
    All of the above
Question 31Single Answer
Which device is commonly used in inverter circuits?
  1. A
    SCR
  2. B
    TRIAC
  3. C
    DIAC
  4. D
    Zener Diode
Question 32Single Answer
Which semiconductor device acts like a switch?
  1. A
    Diode
  2. B
    Transistor
  3. C
    Thyristor
  4. D
    Resistor
Question 33Single Answer
In a basic inverter circuit, DC is converted into:
  1. A
    AC
  2. B
    High voltage DC
  3. C
    Pulsed DC
  4. D
    Rectified DC
Question 34Single Answer
Which device is suitable for high-speed switching?
  1. A
    BJT
  2. B
    MOSFET
  3. C
    TRIAC
  4. D
    SCR
Question 35Single Answer
The basic function of a cycloconverter is to:
  1. A
    Convert DC to AC
  2. B
    Convert high frequency AC to low frequency AC
  3. C
    Convert AC to DC
  4. D
    Regulate voltage
Question 36Single Answer
The term “holding current” in an SCR refers to:
  1. A
    The minimum current required to turn it on
  2. B
    The maximum current it can withstand
  3. C
    The current below which it turns off
  4. D
    The current to trigger it
Question 37Single Answer
The turn-on time of a thyristor is:
  1. A
    Very short
  2. B
    Very long
  3. C
    Equal to 1 second
  4. D
    Depends on gate voltage
Question 38Single Answer
Which component protects circuits from over-voltage?
  1. A
    Inductor
  2. B
    Capacitor
  3. C
    Zener Diode
  4. D
    Resistor
Question 39Single Answer
Power factor in an inductive circuit is:
  1. A
    Leading
  2. B
    Lagging
  3. C
    Unity
  4. D
    Zero
Question 40Single Answer
In AM transmission, the bandwidth required is:
  1. A
    Equal to the modulating frequency
  2. B
    Twice the modulating frequency
  3. C
    Equal to the carrier frequency
  4. D
    Zero
Question 41Single Answer
The power amplifier used in the final stage of a transmitter is usually:
  1. A
    Class A
  2. B
    Class B
  3. C
    Class C
  4. D
    Class D
Question 42Single Answer
The ideal modulation index for maximum power efficiency in AM is:
  1. A
    0
  2. B
    5
  3. C
    1
  4. D
    2
Question 43Single Answer
An SCR can be turned off by:
  1. A
    Increasing gate current
  2. B
    Reducing gate voltage
  3. C
    Reducing anode current below holding current
  4. D
    Applying reverse voltage to gate
Question 44Single Answer
Which of the following devices is a bidirectional semiconductor switch?
  1. A
    SCR
  2. B
    TRIAC
  3. C
    DIAC
  4. D
    Zener diode
Question 45Single Answer
Which component is used for voltage regulation in a power supply?
  1. A
    Resistor
  2. B
    Capacitor
  3. C
    Zener diode
  4. D
    Inductor
Question 46Single Answer
The purpose of a heat sink in power electronics is to:
  1. A
    Generate heat
  2. B
    Reduce switching losses
  3. C
    Cool down the device
  4. D
    Increase current
Question 47Single Answer
A full-wave rectifier gives:
  1. A
    Pulsating AC
  2. B
    Smooth AC
  3. C
    Continuous DC
  4. D
    Pulsating DC with both half cycles
Question 48Single Answer
Which of the following devices is used for triggering a TRIAC?
  1. A
    SCR
  2. B
    MOSFET
  3. C
    DIAC
  4. D
    Zener diode
Question 49Single Answer
The output frequency of an inverter is typically:
  1. A
    0 Hz
  2. B
    25 Hz
  3. C
    50 Hz or 60 Hz
  4. D
    100 Hz
Question 50Single Answer
The device used for step-down voltage conversion in power electronics is:
  1. A
    Inverter
  2. B
    Chopper
  3. C
    Transformer
  4. D
    Oscillator
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