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.
Electronics Engineering (Q1–Q25)
- 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. - 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 - 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. - Unit of capacitance?
A. Ohm
B. Henry
C. Farad ?
D. Tesla
Explanation: 1 Farad = 1 Coulomb/Volt. - 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. - 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. - 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 - 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. - 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. - 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. - 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. - 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. - Phase shift in RC circuit at high frequency?
A. 0°
B. 45°
C. 90° ?
D. 180°
Explanation: Capacitive reactance decreases, causing ~90° phase shift. - Ohm’s law formula?
A. V = IR ?
B. P = VI
C. I = P/V
D. V = I²R
Explanation: Voltage equals current multiplied by resistance. - Unit of inductance?
A. Ohm
B. Farad
C. Tesla
D. Henry ?
Explanation: Henry = 1 Weber per Ampere. - Microprocessor 8085 has?
A. 4-bit
B. 8-bit ?
C. 16-bit
D. 32-bit
Explanation: 8085 is an 8-bit microprocessor. - 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. - Ideal Op-Amp input impedance?
A. 0
B. 1 k?
C. 10 k?
D. Infinite ?
Explanation: Ideal op-amp draws no input current. - Which device converts analog to digital?
A. DAC
B. ADC ?
C. Amplifier
D. Oscillator
Explanation: ADC samples and converts analog signals to digital form. - Schmitt Trigger is used for?
A. Amplification
B. Filtering
C. Noise immunity ?
D. Rectification
Explanation: Converts noisy input to clean digital output. - 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. - RC time constant?
A. ? = R × C ?
B. ? = R / C
C. ? = C / R
D. ? = ?(RC)
Explanation: Time for capacitor to charge/discharge ~63%. - Multivibrator generating one pulse?
A. Astable
B. Bistable
C. Monostable ?
D. Schmitt
Explanation: Monostable has one stable state; outputs single pulse. - Frequency of processor clock determines?
A. Memory size
B. Instruction type
C. Speed of processor ?
D. Cache latency
Explanation: Higher clock = faster execution cycles. - Current through diode in forward bias?
A. Depends on applied voltage ?
B. Constant
C. Zero
D. Infinite
Explanation: Exponential relationship per diode equation.
Mechanical Engineering (Q26–Q50)
- Efficiency of ideal Otto cycle depends on?
A. Compression ratio ?
B. Expansion ratio
C. Fuel type
D. Temperature
Explanation: ? = 1 – 1/r^(?–1) - Head developed by centrifugal pump depends on?
A. Impeller diameter & speed ?
B. Flow rate
C. Fluid type
D. Viscosity
Explanation: Head ? impeller diameter² × speed² - Area under stress–strain curve represents?
A. Elasticity
B. Strength
C. Toughness ?
D. Hardness
Explanation: Energy absorbed before fracture. - Unit of dynamic viscosity?
A. Pa
B. N/m²
C. N·s/m² ?
D. kg/m³
Explanation: SI unit of viscosity. - Bernoulli’s theorem applies to?
A. Incompressible, frictionless flow ?
B. Compressible flow
C. Turbulent flow
D. Viscous flow
Explanation: Assumes ideal fluid. - 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. - Gear ratio formula?
A. N1/N2
B. N1×N2
C. D1/D2
D. N2/N1 ?
Explanation: Ratio of teeth determines speed. - 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. - Efficiency of Carnot engine?
A. 1 – Tc/Th ?
B. W/Qh
C. Qc/Qh
D. 1 – Th/Tc
Explanation: Maximum possible efficiency. - Reynolds number formula?
A. ?v²D/?
B. ?vD/? ?
C. vD/?
D. ?v/?D
Explanation: Dimensionless number characterizing flow regime. - 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. - 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 - Shear stress formula?
A. ? = F/A ?
B. ? = FL
C. ? = ?
D. ? = ?V
Explanation: Force per unit area. - Torque of rotating shaft?
A. T = F
B. T = F/L
C. T = Fr ?
D. T = Fr²
Explanation: Torque = force × lever arm. - Work done in isothermal expansion?
A. Zero
B. W = nRT ln(V2/V1) ?
C. W = P?V
D. Constant
Explanation: Temperature constant. - Spring constant unit?
A. N
B. m
C. N·m
D. N/m ?
Explanation: Force per unit displacement. - Coefficient of friction?
A. ? = F/N ?
B. ? = N/F
C. ? = F*R
D. ? = T/F
Explanation: Ratio of friction to normal force. - 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. - Critical speed of shaft occurs when?
A. Always
B. Resonance occurs ?
C. Below natural frequency
D. No vibration
Explanation: Avoid operating at resonance. - Work done in throttling process?
A. Zero ?
B. Positive
C. Negative
D. Variable
Explanation: Enthalpy constant; no work done. - Modulus of rigidity?
A. Stress / strain
B. Young’s modulus
C. Shear stress / Shear strain ?
D. Bulk modulus
Explanation: G = ?/? - Fluid static pressure?
A. ?v²/2
B. ?gh ?
C. P0
D. ?gh
Explanation: Hydrostatic pressure formula. - Efficiency of screw jack?
A. cos ? / (cos ? + ?)
B. ? / tan ?
C. tan ? / ?
D. tan ? / (tan ? + ?) ?
Explanation: ? = lead angle, ? = friction. - Air standard cycle?
A. Idealized engine cycle ?
B. Diesel engine only
C. Gas turbine only
D. Real engine cycle
Explanation: Used for thermodynamic analysis. - 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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