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BHEL MCQs

Practice BHEL-oriented Electronics & Telecommunication Engineering MCQs with answers and explanations for technical exam preparation. Questions are arranged in pages of up to 100.

Question 6
Control SystemsStability

For a stable continuous-time linear system, poles of the closed-loop transfer function should generally lie in which region of the s-plane?

  • ARight half-plane
  • BLeft half-plane
  • COnly on the imaginary axis
  • DAt the origin only
Report an error
Correct Answer: B. Left half-plane
Explanation: For an asymptotically stable continuous-time LTI closed-loop system, its poles lie in the left half of the s-plane.
Reference: Classical control-system stability criterion
Question 7
Digital ElectronicsLogic Gates

Which pair consists entirely of universal gates?

  • AAND and OR
  • BXOR and XNOR
  • CNAND and NOR
  • DNOT and AND
Report an error
Correct Answer: C. NAND and NOR
Explanation: Either NAND gates alone or NOR gates alone can be used to implement any Boolean function.
Reference: Universal logic gates
Question 10
Digital ElectronicsK-Map

A Karnaugh map is primarily used to?

  • AGenerate clock pulses
  • BSimplify Boolean expressions
  • CConvert analog signals to digital
  • DStore binary data
Report an error
Correct Answer: B. Simplify Boolean expressions
Explanation: A Karnaugh map provides a graphical method for minimizing Boolean expressions.
Reference: Karnaugh-map minimization
Question 12
Digital ElectronicsCombinational Circuits

A half adder adds?

  • ATwo single-bit binary inputs
  • BThree single-bit binary inputs
  • CTwo 4-bit numbers only
  • DOne binary input and one decimal input
Report an error
Correct Answer: A. Two single-bit binary inputs
Explanation: A half adder adds two one-bit inputs and produces Sum and Carry outputs.
Reference: Half-adder fundamentals
Question 13
Digital ElectronicsMultiplexers & Demultiplexers

A multiplexer is commonly described as a?

  • AOne-to-many data distributor
  • BMany-to-one data selector
  • CBinary storage element
  • DFrequency divider only
Report an error
Correct Answer: B. Many-to-one data selector
Explanation: A multiplexer selects one of several input lines and connects it to a single output.
Reference: Multiplexer fundamentals
Question 14
Digital ElectronicsEncoders & Decoders

An encoder generally converts?

  • A2ⁿ input lines into n output lines
  • Bn input lines into 2ⁿ output lines
  • CAnalog voltage directly into frequency only
  • DSerial data into analog data
Report an error
Correct Answer: A. 2ⁿ input lines into n output lines
Explanation: A conventional binary encoder maps one active line among 2ⁿ inputs to an n-bit code.
Reference: Binary encoder fundamentals
Question 17
Digital ElectronicsNumber Systems & Codes

The radix of the binary number system is?

  • A2
  • B8
  • C10
  • D16
Report an error
Correct Answer: A. 2
Explanation: Binary uses two symbols, 0 and 1, so its radix is 2.
Reference: Standard digital electronics fundamentals
Question 21
Digital ElectronicsLogic Gates

A two-input XOR gate produces HIGH output when?

  • ABoth inputs are LOW
  • BBoth inputs are HIGH
  • CThe two inputs are different
  • DAt least one input is HIGH including both HIGH
Report an error
Correct Answer: C. The two inputs are different
Explanation: For a two-input XOR gate, the output is HIGH when exactly one input is HIGH, meaning the inputs differ.
Reference: XOR truth table
Question 22
Digital ElectronicsLogic Gates

A NOT gate is also called a?

  • ABuffer
  • BInverter
  • CComparator
  • DEncoder
Report an error
Correct Answer: B. Inverter
Explanation: A NOT gate complements its input and is therefore called an inverter.
Reference: Basic logic gates
Question 24
Digital ElectronicsCounters

A synchronous counter differs from a ripple counter because in a synchronous counter?

  • AOnly the first flip-flop receives the clock
  • BAll flip-flops are clocked simultaneously
  • CNo flip-flop requires a clock
  • DThe output is always asynchronous
Report an error
Correct Answer: B. All flip-flops are clocked simultaneously
Explanation: In a synchronous counter, the same clock is applied to all flip-flops, so state changes occur together rather than rippling stage by stage.
Reference: Standard digital electronics: synchronous counters
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Question 27
Digital ElectronicsCounters

A decade counter is also known as a?

  • AMOD-2 counter
  • BMOD-8 counter
  • CMOD-10 counter
  • DMOD-16 counter
Report an error
Correct Answer: C. MOD-10 counter
Explanation: A decade counter cycles through ten states, so it is a MOD-10 counter.
Reference: Standard digital electronics: decade counters
Question 28
Digital ElectronicsCounters

In a ripple counter, the propagation delay generally?

  • AIs independent of the number of stages
  • BAccumulates through successive flip-flop stages
  • CBecomes exactly zero
  • DOccurs only in the first stage
Report an error
Correct Answer: B. Accumulates through successive flip-flop stages
Explanation: Ripple counters are asynchronous; each stage is triggered by the preceding stage, so propagation delays accumulate.
Reference: Standard digital electronics: asynchronous counters
Question 29
Digital ElectronicsShift Registers

A shift register is primarily used to?

  • AAmplify analog voltage
  • BStore and shift binary data
  • CGenerate sinusoidal signals
  • DMeasure resistance
Report an error
Correct Answer: B. Store and shift binary data
Explanation: A shift register is a group of flip-flops used to store binary information and shift it from one stage to another.
Reference: Standard digital electronics: shift registers
Question 30
Digital ElectronicsLogic Families

Compared with classic TTL, CMOS logic is especially known for low?

  • AInput impedance
  • BStatic power consumption
  • CNoise margin
  • DFan-out in every case
Report an error
Correct Answer: B. Static power consumption
Explanation: A major advantage of CMOS logic is very low static power consumption, particularly when not switching.
Reference: Standard digital electronics: CMOS characteristics
Question 32
Digital ElectronicsLogic Families

Fan-out of a logic gate refers to?

  • AThe number of outputs inside the gate
  • BThe maximum number of standard logic inputs its output can drive reliably
  • CThe propagation delay through the gate
  • DThe number of power-supply pins
Report an error
Correct Answer: B. The maximum number of standard logic inputs its output can drive reliably
Explanation: Fan-out specifies how many compatible logic inputs one gate output can drive while maintaining valid logic levels.
Reference: Standard digital electronics: fan-out
Question 33
Digital ElectronicsCounters

A ring counter is commonly formed by?

  • AConnecting the complemented output permanently to ground
  • BFeeding the last flip-flop output back to the first flip-flop input
  • CRemoving the clock from every flip-flop
  • DConnecting all outputs directly together
Report an error
Correct Answer: B. Feeding the last flip-flop output back to the first flip-flop input
Explanation: A basic ring counter is a shift register in which the output of the last stage is fed back to the input of the first stage.
Reference: Standard digital electronics: ring counters
Question 34
Digital ElectronicsTiming & Clock

Propagation delay of a digital gate is the time between?

  • AApplying power and permanently damaging the gate
  • BAn input transition and the corresponding output transition
  • CTwo unrelated clock cycles only
  • DWriting and erasing ROM
Report an error
Correct Answer: B. An input transition and the corresponding output transition
Explanation: Propagation delay is the finite time from a relevant change at a gate input to the resulting change at its output.
Reference: Standard digital electronics: propagation delay
Question 35
Digital ElectronicsCounters

A Johnson counter is also called a?

  • AStraight ring counter
  • BTwisted-ring counter
  • CBinary adder
  • DPriority encoder
Report an error
Correct Answer: B. Twisted-ring counter
Explanation: A Johnson counter feeds the complemented output of the last stage back to the first stage and is commonly called a twisted-ring counter.
Reference: Standard digital electronics: Johnson counters
Question 37
Digital ElectronicsMemory

Which memory is volatile?

  • AROM
  • BEEPROM
  • CRAM
  • DFlash memory
Report an error
Correct Answer: C. RAM
Explanation: RAM is volatile because its stored data is normally lost when power is removed.
Reference: Standard digital electronics: semiconductor memory
Question 39
Digital ElectronicsMemory

SRAM stores each bit using primarily?

  • AA capacitor that must be periodically refreshed
  • BA bistable latch/flip-flop-like cell
  • CA magnetic tape element
  • DAn optical sensor
Report an error
Correct Answer: B. A bistable latch/flip-flop-like cell
Explanation: SRAM uses bistable circuitry for each stored bit and does not require periodic refresh while powered.
Reference: Standard digital electronics: SRAM
Question 40
Digital ElectronicsMemory

DRAM requires periodic refresh mainly because each bit is stored as?

  • ACharge on a capacitor
  • BA permanent fuse state
  • CA mechanical switch position
  • DA magnetic core only
Report an error
Correct Answer: A. Charge on a capacitor
Explanation: DRAM cells store information as electrical charge on capacitors, and leakage requires periodic refreshing.
Reference: Standard digital electronics: DRAM
Question 41
Digital ElectronicsMemory

EEPROM can be erased and reprogrammed?

  • AOnly by ultraviolet light
  • BElectrically
  • COnly by replacing the chip
  • DOnly while manufacturing
Report an error
Correct Answer: B. Electrically
Explanation: EEPROM stands for electrically erasable programmable read-only memory and can be erased and programmed electrically.
Reference: Standard digital electronics: EEPROM
Question 42
Digital ElectronicsADC & DAC

An ADC performs which conversion?

  • ADigital to analog
  • BAnalog to digital
  • CFrequency to resistance only
  • DBinary to decimal display only
Report an error
Correct Answer: B. Analog to digital
Explanation: An analog-to-digital converter converts an analog input quantity into a digital representation.
Reference: Standard digital electronics: ADC
Question 43
Digital ElectronicsADC & DAC

A DAC performs which conversion?

  • AAnalog to digital
  • BDigital to analog
  • CAC to DC power conversion
  • DSerial to parallel only
Report an error
Correct Answer: B. Digital to analog
Explanation: A digital-to-analog converter converts a digital code into a corresponding analog output.
Reference: Standard digital electronics: DAC
Question 45
Digital ElectronicsADC & DAC

Increasing the number of bits of an ideal ADC generally?

  • AReduces the number of available codes
  • BImproves resolution
  • CEliminates the need for sampling
  • DMakes the output analog
Report an error
Correct Answer: B. Improves resolution
Explanation: More bits provide more quantization levels, allowing smaller input changes to be represented and therefore improving resolution.
Reference: Standard digital electronics: ADC resolution
Question 46
Digital ElectronicsLogic Families

TTL is an abbreviation for?

  • ATransistor-Transistor Logic
  • BTransfer-Timing Logic
  • CTri-state Transfer Logic
  • DTransistor-Tuned Line
Report an error
Correct Answer: A. Transistor-Transistor Logic
Explanation: TTL stands for Transistor-Transistor Logic, a family of digital integrated circuits based on bipolar junction transistors.
Reference: Standard digital electronics: TTL
Question 47
Digital ElectronicsLogic Families

CMOS is an abbreviation for?

  • AComplementary Metal-Oxide-Semiconductor
  • BCommon Mode Output System
  • CControlled Memory Output Switch
  • DComplementary Magnetic Output Stage
Report an error
Correct Answer: A. Complementary Metal-Oxide-Semiconductor
Explanation: CMOS stands for Complementary Metal-Oxide-Semiconductor.
Reference: Standard digital electronics: CMOS
Question 48
Digital ElectronicsFlip-Flops

For a JK flip-flop, if J = 1 and K = 1, the next state is?

  • AAlways 0
  • BAlways 1
  • CThe complement of the present state
  • DEqual to the present state
Report an error
Correct Answer: C. The complement of the present state
Explanation: With J = K = 1, a JK flip-flop toggles, so Q(next) is the complement of Q(present).
Reference: Standard digital electronics: JK flip-flop characteristic
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Question 51
Digital ElectronicsFlip-Flops

The race-around condition in a level-triggered JK flip-flop can occur when?

  • AJ = K = 0
  • BJ = 0, K = 1
  • CJ = K = 1 and the clock pulse is sufficiently wide
  • DJ = 1, K = 0 only
Report an error
Correct Answer: C. J = K = 1 and the clock pulse is sufficiently wide
Explanation: When J = K = 1, repeated toggling can occur during a sufficiently long active clock level if the propagation delay permits multiple changes.
Reference: Standard digital electronics: race-around condition
Question 52
Digital ElectronicsFlip-Flops

A common method of avoiding race-around in a JK flip-flop is to use?

  • AA master-slave or edge-triggered flip-flop
  • BA larger supply voltage only
  • CAn OR gate at the output
  • DA resistor in series with every input
Report an error
Correct Answer: A. A master-slave or edge-triggered flip-flop
Explanation: Master-slave or edge-triggered operation restricts the effective state transition and prevents repeated toggling during one clock interval.
Reference: Standard digital electronics: JK flip-flops
Question 64
Digital ElectronicsBoolean Algebra

Simplify the Boolean expression A + A·B.

  • AA
  • BB
  • CA + B
  • DA·B
Report an error
Correct Answer: A. A
Explanation: By the absorption law, A + AB = A.
Reference: Standard digital electronics: Boolean absorption law
Question 65
Digital ElectronicsBoolean Algebra

Simplify the Boolean expression A(A + B).

  • AA
  • BB
  • CA + B
  • DAB
Report an error
Correct Answer: A. A
Explanation: By the absorption law, A(A + B) = A.
Reference: Standard digital electronics: Boolean absorption law
Question 66
Digital ElectronicsBoolean Algebra

According to De Morgan’s theorem, the complement of (A + B) is?

  • AA complement + B complement
  • BA complement · B complement
  • CA · B
  • DA + B
Report an error
Correct Answer: B. A complement · B complement
Explanation: De Morgan's theorem gives complement(A + B) = complement(A) · complement(B).
Reference: Standard digital electronics: De Morgan's theorem
Question 75
Digital ElectronicsEncoders & Decoders

A priority encoder differs from an ordinary encoder because it?

  • AHas no outputs
  • BAssigns priority when more than one input is active
  • CAlways converts analog signals
  • DStores the encoded data permanently
Report an error
Correct Answer: B. Assigns priority when more than one input is active
Explanation: A priority encoder resolves simultaneous active inputs by producing the code corresponding to the highest-priority asserted input.
Reference: Standard digital electronics: priority encoders
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Question 78
Digital ElectronicsMultiplexers & Demultiplexers

An 8-to-1 multiplexer can directly implement a Boolean function of three variables by connecting the variables primarily to its?

  • AData outputs
  • BSelect inputs
  • CPower pins
  • DEnable output only
Report an error
Correct Answer: B. Select inputs
Explanation: Three variables provide 2^3 = 8 combinations, so they can drive the three select inputs while the data inputs are set according to the function truth table.
Reference: Standard digital electronics: implementing logic with multiplexers
Question 80
Digital ElectronicsCombinational Circuits

For a full adder, the carry-out expression can be written as?

  • AA XOR B XOR Cin
  • BAB + ACin + BCin
  • CA + B + Cin
  • DABCin only
Report an error
Correct Answer: B. AB + ACin + BCin
Explanation: The full-adder carry is 1 whenever at least two of the three inputs are 1, giving Cout = AB + ACin + BCin.
Reference: Standard digital electronics: full adder
Question 81
Digital ElectronicsNumber Systems & Codes

The binary result of adding 1011 and 0101 is?

  • A10000
  • B01110
  • C11110
  • D10100
Report an error
Correct Answer: A. 10000
Explanation: Binary 1011 is 11 and 0101 is 5. Their sum is 16, which is binary 10000.
Reference: Standard digital electronics: binary arithmetic
Question 82
Digital ElectronicsTiming & Clock

For an edge-triggered D flip-flop, the input D must remain stable for specified intervals immediately before and after the active clock edge. These intervals are called?

  • ARise time and fall time
  • BSetup time and hold time
  • CPropagation time and recovery time
  • DAccess time and cycle time
Report an error
Correct Answer: B. Setup time and hold time
Explanation: Setup time is the minimum interval D must be stable before the active clock edge, while hold time is the minimum interval it must remain stable afterward.
Reference: Standard digital electronics: flip-flop timing
Question 83
Digital ElectronicsTiming & Clock

If a flip-flop’s setup or hold time requirement is violated, the device may enter?

  • ASaturation only
  • BMetastability
  • CPermanent tri-state operation
  • DFrequency multiplication
Report an error
Correct Answer: B. Metastability
Explanation: Violating setup or hold requirements can leave a flip-flop temporarily in an indeterminate or metastable state before it resolves to a valid logic level.
Reference: Standard digital electronics: metastability
Question 87
Digital ElectronicsADC & DAC

Which ADC architecture is generally known for very high conversion speed because it uses many comparators in parallel?

  • ADual-slope ADC
  • BFlash ADC
  • CSuccessive-approximation ADC
  • DIntegrating ADC only
Report an error
Correct Answer: B. Flash ADC
Explanation: A flash ADC compares the input simultaneously against many reference levels, providing very fast conversion at the cost of many comparators.
Reference: Standard digital electronics: ADC architectures
Question 88
Digital ElectronicsADC & DAC

A successive-approximation ADC determines the digital output primarily by?

  • ATesting bits through a binary-search-like sequence
  • BCounting indefinitely until power is removed
  • CUsing only one fixed comparator threshold with no DAC
  • DDirectly storing the analog voltage as binary charge
Report an error
Correct Answer: A. Testing bits through a binary-search-like sequence
Explanation: A SAR ADC successively tests candidate bits, effectively performing a binary search using an internal DAC and comparator.
Reference: Standard digital electronics: SAR ADC
Question 91
Digital ElectronicsNumber Systems & Codes

The Gray-code equivalent of binary 1011 is?

  • A1110
  • B1010
  • C1101
  • D1001
Report an error
Correct Answer: A. 1110
Explanation: For binary-to-Gray conversion, the MSB is unchanged and each following Gray bit is the XOR of adjacent binary bits: 1, 1 XOR 0 = 1, 0 XOR 1 = 1, 1 XOR 1 = 0, giving 1110.
Reference: Standard digital electronics: Gray code conversion
Question 95
Digital ElectronicsMemory

A 4K × 8 memory has a total capacity of?

  • A4 Kbits
  • B8 Kbits
  • C32 Kbits
  • D64 Kbits
Report an error
Correct Answer: C. 32 Kbits
Explanation: There are 4096 words of 8 bits each, giving 4096 × 8 = 32768 bits = 32 Kbits.
Reference: Standard digital electronics: memory capacity
Question 97
Electronic Devices & CircuitsSemiconductor Fundamentals

Doping pure silicon with a pentavalent impurity such as phosphorus generally produces?

  • AP-type semiconductor
  • BN-type semiconductor
  • CIntrinsic semiconductor
  • DInsulating material
Report an error
Correct Answer: B. N-type semiconductor
Explanation: Pentavalent donor atoms contribute extra electrons, making electrons the majority carriers in an n-type semiconductor.
Reference: Standard semiconductor electronics: doping
Question 98
Electronic Devices & CircuitsSemiconductor Fundamentals

In a p-type semiconductor, the majority charge carriers are?

  • AElectrons
  • BHoles
  • CNeutrons
  • DPositive ions moving through the lattice
Report an error
Correct Answer: B. Holes
Explanation: Trivalent acceptor doping creates holes as the majority mobile carriers in p-type material.
Reference: Standard semiconductor electronics: p-type material
Question 99
Electronic Devices & CircuitsPN Junction Diode

The depletion region of a PN junction mainly contains?

  • AOnly freely moving electrons
  • BOnly freely moving holes
  • CImmobile ionized donor and acceptor atoms
  • DNo electric field
Report an error
Correct Answer: C. Immobile ionized donor and acceptor atoms
Explanation: Carrier diffusion near the junction leaves uncovered fixed ionized donors and acceptors, forming the space-charge or depletion region.
Reference: Standard semiconductor electronics: PN junction
Question 100
Electronic Devices & CircuitsPN Junction Diode

Forward biasing a PN junction generally causes the depletion width to?

  • AIncrease
  • BDecrease
  • CRemain exactly unchanged
  • DBecome infinite
Report an error
Correct Answer: B. Decrease
Explanation: Forward bias opposes the built-in junction field, reducing the barrier potential and narrowing the depletion region.
Reference: Standard semiconductor electronics: diode biasing
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