BEL Probationary Engineer (E-II Grade) 2025 – 100 Questions with Answers

Prepare for BEL Probationary Engineer (E-II Grade) 2025 exam with our comprehensive 100-question guide. Covers Electronics, Mechanical, Electrical, and Computer Science Engineering with answers and explanations for effective exam preparation.

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Electronics Engineering (Q1–Q25)

1. The function of a Zener diode is?
   A. Rectifier
   B. Voltage Regulator ?
   C. Amplifier
   D. Filter
   Explanation: Operates in reverse breakdown to maintain constant voltage.
2. Modulation index of AM = 0.5, carrier power = 100 W. Total power?
   A. 112.5 W ?
   B. 125 W
   C. 150 W
   D. 100 W
   Explanation: Ptotal=Pc(1+?2/2)=112.5WP_{total} = P_c (1 + ?^2/2) = 112.5 WPtotal?=Pc?(1+?2/2)=112.5W
3. High-speed data transmission medium?
   A. Coaxial
   B. Optical Fiber ?
   C. Twisted Pair
   D. Waveguide
   Explanation: Fiber optic cables offer high bandwidth and low attenuation.
4. Unit of capacitance?
   A. Ohm
   B. Henry
   C. Farad ?
   D. Tesla
   Explanation: 1 Farad = 1 Coulomb/Volt.
5. Flip-flop used for storage?
   A. JK Flip-Flop
   B. D Flip-Flop
   C. T Flip-Flop
   D. SR Flip-Flop ?
   Explanation: SR Flip-Flop is a basic memory element storing one bit.
6. Amplifier with no phase shift between input and output?
   A. Inverting
   B. Non-inverting ?
   C. Differential
   D. Common emitter
   Explanation: Non-inverting amplifiers maintain input and output phase.
7. Frequency of a 4-pole, 1500 rpm generator?
   A. 50 Hz ?
   B. 60 Hz
   C. 25 Hz
   D. 75 Hz
   Explanation: f=(P×N)/120=50Hzf = (P \times N)/120 = 50 Hzf=(P×N)/120=50Hz
8. Type of ADC offering balance between speed and accuracy?
   A. Flash ADC
   B. Dual Slope
   C. Successive Approximation ?
   D. Sigma-Delta
   Explanation: SAR ADC converts analog signals efficiently.
9. MOSFET stands for?
   A. Metal Oxide Semiconductor FET
   B. Metal Oxide Semiconductor FET ?
   C. Metal On Silicon FET
   D. Magnetic Oscillator Semiconductor FET
   Explanation: Voltage-controlled transistor.
10. BJT operates in which regions?
    A. Active only
    B. Cutoff only
    C. Active, Cutoff, Saturation ?
    D. Saturation only
    Explanation: BJT has three regions for amplification and switching.
11. Bandwidth of an ideal low-pass filter?
    A. 0 to f_c ?
    B. f_c to ?
    C. –f_c to f_c
    D. Depends on load
    Explanation: Passes frequencies from 0 Hz to cutoff f_c.
12. Control system with feedback is called?
    A. Open Loop
    B. Closed Loop ?
    C. Linear
    D. Non-linear
    Explanation: Closed-loop systems use feedback to control output.
13. Phase shift in RC circuit at high frequency?
    A. 0°
    B. 45°
    C. 90° ?
    D. 180°
    Explanation: Capacitive reactance decreases, causing ~90° phase shift.
14. Ohm’s law formula?
    A. V = IR ?
    B. P = VI
    C. I = P/V
    D. V = I²R
    Explanation: Voltage equals current multiplied by resistance.
15. Unit of inductance?
    A. Ohm
    B. Farad
    C. Tesla
    D. Henry ?
    Explanation: Henry = 1 Weber per Ampere.
16. Microprocessor 8085 has?
    A. 4-bit
    B. 8-bit ?
    C. 16-bit
    D. 32-bit
    Explanation: 8085 is an 8-bit microprocessor.
17. Sample and hold circuit function?
    A. Amplifies voltage
    B. Filters noise
    C. Maintains voltage ?
    D. Converts digital to analog
    Explanation: Holds sampled voltage stable for ADC conversion.
18. Ideal Op-Amp input impedance?
    A. 0
    B. 1 k?
    C. 10 k?
    D. Infinite ?
    Explanation: Ideal op-amp draws no input current.
19. Which device converts analog to digital?
    A. DAC
    B. ADC ?
    C. Amplifier
    D. Oscillator
    Explanation: ADC samples and converts analog signals to digital form.
20. Schmitt Trigger is used for?
    A. Amplification
    B. Filtering
    C. Noise immunity ?
    D. Rectification
    Explanation: Converts noisy input to clean digital output.
21. PWM stands for?
    A. Pulse Width Modulator
    B. Pulse Width Modulation ?
    C. Phase Width Modulation
    D. Pulse Wave Modulation
    Explanation: Modulates pulse width to control power.
22. RC time constant?
    A. ? = R × C ?
    B. ? = R / C
    C. ? = C / R
    D. ? = ?(RC)
    Explanation: Time for capacitor to charge/discharge ~63%.
23. Multivibrator generating one pulse?
    A. Astable
    B. Bistable
    C. Monostable ?
    D. Schmitt
    Explanation: Monostable has one stable state; outputs single pulse.
24. Frequency of processor clock determines?
    A. Memory size
    B. Instruction type
    C. Speed of processor ?
    D. Cache latency
    Explanation: Higher clock = faster execution cycles.
25. Current through diode in forward bias?
    A. Depends on applied voltage ?
    B. Constant
    C. Zero
    D. Infinite
    Explanation: Exponential relationship per diode equation.

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Mechanical Engineering (Q26–Q50)

26. Efficiency of ideal Otto cycle depends on?
    A. Compression ratio ?
    B. Expansion ratio
    C. Fuel type
    D. Temperature
    Explanation: ? = 1 – 1/r^(?–1)
27. Head developed by centrifugal pump depends on?
    A. Impeller diameter & speed ?
    B. Flow rate
    C. Fluid type
    D. Viscosity
    Explanation: Head ? impeller diameter² × speed²
28. Area under stress–strain curve represents?
    A. Elasticity
    B. Strength
    C. Toughness ?
    D. Hardness
    Explanation: Energy absorbed before fracture.
29. Unit of dynamic viscosity?
    A. Pa
    B. N/m²
    C. N·s/m² ?
    D. kg/m³
    Explanation: SI unit of viscosity.
30. Bernoulli’s theorem applies to?
    A. Incompressible, frictionless flow ?
    B. Compressible flow
    C. Turbulent flow
    D. Viscous flow
    Explanation: Assumes ideal fluid.
31. Moment of inertia of solid cylinder about axis?
    A. mr²
    B. 0.5mr² ?
    C. 2mr²
    D. 0.25m*r²
    Explanation: Standard formula for solid cylinder.
32. Gear ratio formula?
    A. N1/N2
    B. N1×N2
    C. D1/D2
    D. N2/N1 ?
    Explanation: Ratio of teeth determines speed.
33. Work done in adiabatic process?
    A. Zero
    B. Depends on temperature
    C. Integral PdV ?
    D. Constant
    Explanation: No heat transfer; work depends on pressure-volume.
34. Efficiency of Carnot engine?
    A. 1 – Tc/Th ?
    B. W/Qh
    C. Qc/Qh
    D. 1 – Th/Tc
    Explanation: Maximum possible efficiency.
35. Reynolds number formula?
    A. ?v²D/?
    B. ?vD/? ?
    C. vD/?
    D. ?v/?D
    Explanation: Dimensionless number characterizing flow regime.
36. Poiseuille flow applies to?
    A. Turbulent pipe flow
    B. Open channel flow
    C. Laminar pipe flow ?
    D. Rotational flow
    Explanation: Laminar flow in circular pipe.
37. Heat transfer by conduction follows?
    A. Newton’s law
    B. Fourier’s law ?
    C. Stefan–Boltzmann law
    D. Wien’s law
    Explanation: Q = –kA dT/dx
38. Shear stress formula?
    A. ? = F/A ?
    B. ? = FL
    C. ? = ?
    D. ? = ?V
    Explanation: Force per unit area.
39. Torque of rotating shaft?
    A. T = F
    B. T = F/L
    C. T = Fr ?
    D. T = Fr²
    Explanation: Torque = force × lever arm.
40. Work done in isothermal expansion?
    A. Zero
    B. W = nRT ln(V2/V1) ?
    C. W = P?V
    D. Constant
    Explanation: Temperature constant.
41. Spring constant unit?
    A. N
    B. m
    C. N·m
    D. N/m ?
    Explanation: Force per unit displacement.
42. Coefficient of friction?
    A. ? = F/N ?
    B. ? = N/F
    C. ? = F*R
    D. ? = T/F
    Explanation: Ratio of friction to normal force.
43. Power transmitted by shaft?
    A. P = T/2?N
    B. P = TN/60
    C. P = 2?NT/60 ?
    D. P = TN
    Explanation: Standard shaft power formula.
44. Critical speed of shaft occurs when?
    A. Always
    B. Resonance occurs ?
    C. Below natural frequency
    D. No vibration
    Explanation: Avoid operating at resonance.
45. Work done in throttling process?
    A. Zero ?
    B. Positive
    C. Negative
    D. Variable
    Explanation: Enthalpy constant; no work done.
46. Modulus of rigidity?
    A. Stress / strain
    B. Young’s modulus
    C. Shear stress / Shear strain ?
    D. Bulk modulus
    Explanation: G = ?/?
47. Fluid static pressure?
    A. ?v²/2
    B. ?gh ?
    C. P0
    D. ?gh
    Explanation: Hydrostatic pressure formula.
48. Efficiency of screw jack?
    A. cos ? / (cos ? + ?)
    B. ? / tan ?
    C. tan ? / ?
    D. tan ? / (tan ? + ?) ?
    Explanation: ? = lead angle, ? = friction.
49. Air standard cycle?
    A. Idealized engine cycle ?
    B. Diesel engine only
    C. Gas turbine only
    D. Real engine cycle
    Explanation: Used for thermodynamic analysis.
50. Velocity ratio of pulley system?
    A. D2/D1
    B. N1/N2
    C. Driver/Driven ?
    D. D1×D2
    Explanation: Diameter or speed ratio.

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Electrical Engineering (Q51–Q75)

51. Power factor of a purely resistive load?
    A. 0
    B. 0.5
    C. 1 ?
    D. –1
    Explanation: Voltage and current are in phase.
52. Law governing induced EMF?
    A. Lenz’s Law
    B. Faraday’s Law ?
    C. Ohm’s Law
    D. Coulomb’s Law
    Explanation: Induced EMF is proportional to rate of change of magnetic flux.
53. Laminating transformer core reduces?
    A. Hysteresis loss
    B. Eddy current loss ?
    C. Copper loss
    D. Leakage flux
    Explanation: Laminations minimize circulating currents.
54. Single-phase induction motor requires?
    A. Capacitor run only
    B. No starting winding
    C. Series winding
    D. Starting winding ?
    Explanation: To initiate rotation from standstill.
55. RMS value of a sine wave?
    A. Vm
    B. 0.707 × Vm ?
    C. 0.5 × Vm
    D. ?2 × Vm
    Explanation: RMS = Vm/?2
56. Back EMF in DC motor formula?
    A. Eb = k?N ?
    B. Eb = V/R
    C. Eb = I×R
    D. Eb = kI
    Explanation: Proportional to flux and speed.
57. Synchronous speed of 4-pole, 50Hz motor?
    A. 1000 rpm
    B. 1200 rpm
    C. 1500 rpm ?
    D. 3000 rpm
    Explanation: Ns = 120f/P = 120×50/4 = 1500 rpm.
58. Transformer turns ratio?
    A. Np × Ns
    B. Np – Ns
    C. Ns/Np
    D. Np/Ns = Vp/Vs ?
    Explanation: Voltage ratio equals turns ratio.
59. Unit of capacitance?
    A. Farad ?
    B. Henry
    C. Ohm
    D. Tesla
    Explanation: Charge per unit voltage.
60. Reactance of inductor?
    A. R
    B. XL = 2?fL ?
    C. 1/2?fL
    D. L/f
    Explanation: Opposition to AC current.
61. Delta to Wye conversion is used for?
    A. Measuring voltage
    B. Measuring current
    C. Network simplification ?
    D. Reducing loss
    Explanation: Converts three-phase networks.
62. Skin effect occurs in?
    A. DC circuits
    B. Low-frequency AC
    C. Any AC
    D. High-frequency AC ?
    Explanation: Current concentrates near conductor surface.
63. Time constant of RC circuit?
    A. ? = R × C ?
    B. ? = R/C
    C. ? = C/R
    D. ? = ?(RC)
    Explanation: Time for capacitor to charge 63% of final voltage.
64. Overcurrent relay protects?
    A. Generator
    B. Line ?
    C. Transformer
    D. Load
    Explanation: Trips when current exceeds set limit.
65. Efficiency of transformer?
    A. 90%
    B. 95%
    C. ? = Pout/Pin ?
    D. Vp/Vs
    Explanation: Ratio of output to input power.
66. Hysteresis loss depends on?
    A. Material type ?
    B. Supply voltage
    C. Frequency only
    D. Load
    Explanation: Magnetic properties determine hysteresis.
67. Stepper motor type?
    A. AC induction
    B. Permanent magnet ?
    C. Synchronous
    D. DC series
    Explanation: Moves in discrete steps.
68. Frequency of 3-phase system in India?
    A. 60 Hz
    B. 45 Hz
    C. 50 Hz ?
    D. 55 Hz
    Explanation: Standard supply frequency.
69. Impedance of series R-L circuit?
    A. R + L
    B. ?(R² – XL²)
    C. XL
    D. ?(R² + XL²) ?
    Explanation: Pythagorean sum of resistance and reactance.
70. DC series motor speed varies?
    A. Inversely with load ?
    B. Directly with load
    C. Constant
    D. Unrelated
    Explanation: As load increases, speed decreases.
71. Wattmeter measures?
    A. Apparent power
    B. Reactive power
    C. Real power ?
    D. Voltage
    Explanation: Measures true power consumed.
72. Ohm’s law?
    A. V = IR ?
    B. P = VI
    C. I = P/V
    D. V = I²R
73. Capacitor in AC circuit?
    A. Voltage leads current
    B. Current leads voltage ?
    C. Voltage = current
    D. Phase independent
74. Induction motor slip?
    A. Nr/Ns
    B. Ns/Nr
    C. (Ns – Nr)/Ns ?
    D. (Nr – Ns)/Ns
75. Power in 3-phase balanced load?
    A. VL × IL
    B. 3 × VL × IL
    C. 2 × VL × IL
    D. ?3 × VL × IL × PF ?

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Computer Science Engineering (Q76–Q100)

76. Data structure for recursion?
    A. Queue
    B. Stack ?
    C. Linked List
    D. Array
    Explanation: Stores return addresses and local variables.
77. Page replacement algorithm LRU?
    A. FIFO
    B. Least Recently Used ?
    C. MRU
    D. Optimal
    Explanation: Replaces page unused for longest time.
78. Merge sort complexity (average case)?
    A. O(n²)
    B. O(n)
    C. O(n log n) ?
    D. O(log n)
    Explanation: Divide and conquer sorting.
79. Normalization in DB removes?
    A. Data redundancy ?
    B. Indexes
    C. Views
    D. Stored procedures
80. printf(“%d”,5+2*3) output?
    A. 16
    B. 21
    C. 11 ?
    D. 15
    Explanation: Operator precedence: 2*3=6 ? 6+5=11.
81. OS process states?
    A. New, Ready
    B. Ready, Running, Waiting ?
    C. Suspend, Terminate
    D. Deadlock only
82. TCP is?
    A. Connection-oriented ?
    B. Connectionless
    C. Datagram-based
    D. Stateless
83. IPv4 address length?
    A. 64-bit
    B. 32-bit ?
    C. 128-bit
    D. 16-bit
84. Function of DNS?
    A. IP to domain
    B. Encrypt data
    C. Domain to IP ?
    D. Routing
85. Linked list insertion at head?
    A. O(1) ?
    B. O(n)
    C. O(log n)
    D. O(n²)
86. Stack operations?
    A. Insert, Delete
    B. Push and Pop ?
    C. Enqueue, Dequeue
    D. Sort, Merge
87. Queue operations?
    A. Push, Pop
    B. Push, Enqueue
    C. Enqueue, Dequeue ?
    D. Merge, Split
88. Binary search requires?
    A. Any array
    B. Linked list
    C. Hash table
    D. Sorted array ?
89. Recursion base case?
    A. Termination condition ?
    B. Function call
    C. Loop variable
    D. Stack overflow
90. Hash function maps?
    A. Value to key
    B. Index to key
    C. Key to index ?
    D. Node to link
91. Deadlock occurs when?
    A. Mutual exclusion only
    B. All four conditions satisfied ?
    C. Preemption occurs
    D. Starvation
92. Semaphore used for?
    A. Memory allocation
    B. CPU scheduling
    C. Synchronization ?
    D. Networking
93. Compiler converts?
    A. Source to object code ?
    B. Binary to source
    C. OS to executable
    D. Algorithm to data
94. IPv6 address length?
    A. 32-bit
    B. 64-bit
    C. 256-bit
    D. 128-bit ?
95. Preemptive scheduling?
    A. CPU never interrupted
    B. CPU can be interrupted ?
    C. FIFO only
    D. Round-robin only
96. B-tree used in?
    A. Stack
    B. Heap
    C. Database indexing ?
    D. Queue
97. Linear search complexity?
    A. O(n) ?
    B. O(log n)
    C. O(n log n)
    D. O(1)
98. Deadlock prevention method?
    A. Disable preemption
    B. Avoid circular wait ?
    C. Increase memory
    D. Use stack
99. TCP port number range?
    A. 0–1023
    B. 1024–49151
    C. 0–65535 ?
    D. 49152–65535
100. BFS graph traversal complexity?
     A. O(V²)
     B. O(E²)
     C. O(V*E)
     D. O(V+E) ?

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