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BEL Probationary Engineer practice questions

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Question 1Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A 120 V RMS, 60 Hz source drives a series RL circuit with R = 30 Ω and inductive reactance XL = 40 Ω. What is the magnitude of the total impedance?

  1. 50 Ω Correct answer.
  2. 10 Ω
  3. 40 Ω
  4. 70 Ω

Explanation

In a series RL circuit the resistive and reactive components add vectorially, so the impedance magnitude is the square root of (R squared plus XL squared). Substituting 30 and 40 gives the square root of 2500, which equals 50 Ω. Simple arithmetic addition of 30 and 40 is the common error that yields 70 Ω.

Question 2Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a bipolar junction transistor operating in the active region, which relationship describes the collector current for a given base current?

  1. IC = α·IB
  2. IC = IE + IB
  3. IC = β·IB Correct answer.
  4. IC = IB / β

Explanation

Forward-active operation means the base-emitter junction is forward biased and the base-collector junction is reverse biased, so collector current is the base current multiplied by the common-emitter current gain β. Typical β values range from about 50 to 300 for small-signal devices. The relation IC = IE + IB violates Kirchhoff's current law at the transistor node.

Question 3Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A simply supported beam of span L carries a concentrated load P at midspan. What is the maximum bending moment?

  1. P·L
  2. P·L/4 Correct answer.
  3. P·L/2
  4. P·L/8

Explanation

For a simply supported beam with a central point load, each reaction equals P/2 and the moment diagram is triangular, peaking at midspan. Multiplying the reaction by the lever arm L/2 gives P·L/4. The value P·L/8 applies to a uniformly distributed load, not a concentrated one.

Question 4Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

Which data structure provides average O(1) insertion and lookup for keyed records by mapping keys through a hash function?

  1. Hash table Correct answer.
  2. Singly linked list
  3. Min-heap
  4. Balanced binary search tree

Explanation

A hash table computes an index from the key via a hash function, giving constant average time for insertion and lookup when the load factor is controlled. Worst-case behavior degrades to O(n) if many keys collide. The other structures impose ordering or traversal costs that prevent average constant-time keyed access.

Question 5Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a three-phase star-connected system with balanced line voltage VL, what is the phase voltage across each winding?

  1. VL / √3 Correct answer.
  2. VL
  3. VL × √3
  4. VL / 3

Explanation

In a balanced star connection the line voltage is the phasor difference of two phase voltages separated by 120 degrees, giving a factor of √3. Therefore phase voltage equals line voltage divided by √3, roughly 0.577 times VL. In a delta connection the line and phase voltages are equal instead.

Question 6Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

Which material property directly determines the stiffness of a mechanical member in the elastic range?

  1. Poisson's ratio
  2. Yield strength
  3. Young's modulus Correct answer.
  4. Ultimate tensile strength

Explanation

Young's modulus is the slope of the linear portion of the stress-strain curve, so it governs elastic deformation for a given stress. Yield strength marks the onset of plastic flow, and ultimate strength marks fracture resistance, neither of which sets elastic stiffness. Poisson's ratio describes lateral contraction relative to axial strain.

Question 7Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

What does the carry look-ahead technique improve in a binary adder design?

  1. Maximum clock frequency of memory
  2. Propagation delay of the carry chain Correct answer.
  3. Power supply rejection
  4. Gate count of the adder

Explanation

Ripple-carry adders must wait for each carry to propagate through every bit position, which dominates delay for wide words. Carry look-ahead computes generate and propagate terms in parallel to shorten the critical carry path. It typically increases gate count, so reducing area is not its purpose.

Question 8Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A concrete mix specifies a water-cement ratio of 0.45 by mass. If the cement content is 400 kg per cubic meter, what is the water content?

  1. 160 kg
  2. 90 kg
  3. 200 kg
  4. 180 kg Correct answer.

Explanation

Water content equals the water-cement ratio multiplied by cement mass, so 0.45 times 400 kg gives 180 kg per cubic meter. Lower ratios reduce permeability and increase strength but also reduce workability. Dividing cement by the ratio instead would give a meaningless larger value.

Question 9Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A silicon PN junction diode is forward biased with a series resistor. Which statement best describes the resulting operating point?

  1. The diode behaves as an open circuit
  2. The diode current is independent of the series resistor
  3. The diode voltage stays roughly 0.7 V while current is set mainly by the resistor Correct answer.
  4. The diode voltage remains near zero regardless of current

Explanation

Beyond the knee, the forward characteristic is steep, so the diode voltage changes only slightly, near 0.7 V for silicon, while current varies widely. The series resistor therefore sets the current as (VS − 0.7)/R. This load-line intersection defines the operating point.

Question 10Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

An ideal operational amplifier is configured as a non-inverting amplifier with feedback resistor Rf = 90 kΩ and input resistor R1 = 10 kΩ. What is the closed-loop voltage gain?

  1. 10 Correct answer.
  2. 9
  3. 11
  4. 0.1

Explanation

The non-inverting gain equals 1 plus Rf/R1, so 1 + 90/10 = 10. The added unity term reflects that the input signal appears directly at the inverting node through the feedback network. Omitting the 1 gives the incorrect value of 9.

Question 11Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A 4-bit successive approximation ADC has a full-scale input of 5.0 V. What is the nominal resolution (step size) of one least significant bit?

  1. 0.3125 V Correct answer.
  2. 1.25 V
  3. 0.625 V
  4. 0.156 V

Explanation

An n-bit ADC divides full scale into 2^n steps, so 4 bits give 16 steps and 5.0 V divided by 16 equals 0.3125 V per LSB. Resolution improves by a factor of two for each additional bit. Using 8 steps instead of 16 produces the incorrect value of 0.625 V.

Question 12Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A DC shunt motor draws an armature current of 50 A at 220 V. If the armature resistance is 0.2 Ω, what is the back EMF?

  1. 220 V
  2. 200 V
  3. 210 V Correct answer.
  4. 230 V

Explanation

Back EMF equals terminal voltage minus the armature resistive drop, so 220 V minus (50 A × 0.2 Ω = 10 V) gives 210 V. Back EMF is always slightly less than supply voltage in motoring operation. Adding the drop instead would imply generator action.

Question 13Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A single-phase transformer has 500 primary turns and 100 secondary turns. If the primary is connected to 240 V, what is the secondary voltage under no load?

  1. 24 V
  2. 1200 V
  3. 240 V
  4. 48 V Correct answer.

Explanation

The voltage ratio equals the turns ratio, so secondary voltage is 240 V × (100/500) = 48 V. This is a step-down transformer because the secondary has fewer turns. Multiplying instead of dividing by the ratio produces the incorrect value of 1200 V.

Question 14Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A cantilever beam of length L carries a point load P at its free end. What is the maximum deflection at the free end, given flexural rigidity EI?

  1. 5P·L⁴/(384EI)
  2. P·L²/(2EI)
  3. P·L³/(3EI) Correct answer.
  4. P·L³/(8EI)

Explanation

Integrating the bending moment twice for a cantilever with an end load yields a free-end deflection of P·L³ divided by 3EI. The cubic dependence on length shows why small length increases sharply raise deflection. The expression with 384 in the denominator applies to a simply supported beam under distributed load.

Question 15Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a four-bar linkage, a mechanism is classified as a crank-rocker based on which condition?

  1. All links are equal in length
  2. The longest link is the coupler
  3. The shortest link is adjacent to the fixed frame and Grashof's inequality is satisfied Correct answer.
  4. The shortest link is the frame

Explanation

Grashof's criterion states that the sum of the shortest and longest links must not exceed the sum of the other two for continuous relative rotation. When the shortest link is adjacent to the frame and that inequality holds, the shortest link can fully rotate as a crank while the opposite link rocks. If the shortest link is the frame itself, the result is a double-crank.

Question 16Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A steel shaft transmits 15 kW at 1500 rpm. What is the approximate torque on the shaft?

  1. 955 N·m
  2. 95.5 N·m Correct answer.
  3. 10 N·m
  4. 150 N·m

Explanation

Torque equals power divided by angular velocity in radians per second. Angular velocity is 1500 × 2π/60 ≈ 157 rad/s, so 15000 W divided by 157 rad/s gives about 95.5 N·m. Forgetting the 2π conversion and using rpm directly yields a torque that is off by a factor of about 9.55.

Question 17Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A Carnot engine operates between a hot reservoir at 600 K and a cold reservoir at 300 K. What is its thermal efficiency?

  1. 100%
  2. 33%
  3. 50% Correct answer.
  4. 25%

Explanation

Carnot efficiency equals 1 minus the ratio of cold to hot absolute temperature, so 1 − 300/600 = 0.5, or 50 percent. This is the maximum possible efficiency for any engine operating between those temperatures. Using Celsius values instead of kelvin would give a different and incorrect result.

Question 18Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a process control loop, what is the primary function of a PID controller's integral term?

  1. To amplify high-frequency noise
  2. To set the controller's sampling rate
  3. To eliminate steady-state offset by accumulating past error Correct answer.
  4. To add derivative damping to the response

Explanation

The integral term sums the error over time, so any persistent offset drives the controller output until the error returns to zero. This eliminates the steady-state error that proportional action alone leaves behind. Excessive integral gain can cause overshoot and oscillation, which is why tuning matters.

Question 19Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

Which memory type is non-volatile and can be erased and reprogrammed electrically in blocks, making it common for firmware storage?

  1. SRAM
  2. DRAM
  3. Flash memory Correct answer.
  4. Cache memory

Explanation

Flash memory retains data without power and supports in-system electrical erasure, typically in blocks, which suits firmware and embedded code storage. SRAM and DRAM are volatile and lose contents when power is removed. Cache memory is a fast volatile tier near the processor.

Question 20Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A process uses a virtual memory system with 32-bit virtual addresses and 4 KB pages. How many virtual pages can a process address?

  1. 2^32
  2. 2^24
  3. 2^12
  4. 2^20 Correct answer.

Explanation

A 4 KB page size means 12 bits are used for the page offset, leaving 20 bits for the page number in a 32-bit address. Therefore the number of virtual pages is 2^20, about one million. Confusing the offset count with page count leads to the value 2^12.

Question 21Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A relation in a relational database is in third normal form (3NF). Which dependency type must it avoid?

  1. A multivalued dependency on the primary key
  2. A full functional dependency on the whole primary key
  3. A transitive dependency of a non-key attribute on a candidate key Correct answer.
  4. A foreign-key reference to another relation

Explanation

3NF requires that no non-prime attribute depends transitively on a candidate key through another non-prime attribute. Full functional dependencies on the whole key are required at 2NF and remain acceptable. Multivalued dependencies are the concern of fourth normal form.

Question 22Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A soil sample has a void ratio of 0.60 and a specific gravity of solids of 2.70. What is its dry unit weight in kN/m³, taking the unit weight of water as 9.81 kN/m³?

  1. 26.5 kN/m³
  2. 18.0 kN/m³
  3. 14.7 kN/m³
  4. 16.6 kN/m³ Correct answer.

Explanation

Dry unit weight equals Gs times the unit weight of water divided by (1 + e). Substituting 2.70 × 9.81 / 1.60 gives approximately 16.6 kN/m³. Forgetting to add 1 to the void ratio would overstate the value substantially.

Question 23Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A three-phase induction motor has a synchronous speed of 1500 rpm and runs at 1440 rpm at full load. What is the percentage slip?

  1. 6.0%
  2. 10.0%
  3. 4.0% Correct answer.
  4. 2.5%

Explanation

Slip equals synchronous speed minus rotor speed, divided by synchronous speed, so (1500 − 1440)/1500 = 0.04, or 4 percent. Slip increases with mechanical load until breakdown torque is reached. Using rotor speed as the denominator would give a slightly different and incorrect figure.

Question 24Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a CMOS logic gate, dynamic power dissipation is best approximated by which expression, where C is load capacitance, V is supply voltage, and f is switching frequency?

  1. C·V²·f Correct answer.
  2. V²·f / C
  3. C·V·f
  4. C·V²·f²

Explanation

Each switching cycle charges and discharges the load capacitance, dissipating energy proportional to C·V² per cycle, so multiplying by switching frequency gives average dynamic power. The quadratic dependence on supply voltage is why voltage scaling is such an effective power-reduction technique. Short-circuit and leakage power add to this estimate.

Question 25Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A feedback control system has an open-loop transfer function with a dominant pole pair giving a phase margin of 15 degrees. What behavior is expected in closed-loop response?

  1. Well-damped response with minimal overshoot
  2. Complete instability with no output
  3. Large overshoot and possible sustained oscillation Correct answer.
  4. Critically damped response with zero overshoot

Explanation

Phase margin is a direct indicator of closed-loop damping; a margin near 15 degrees corresponds to a lightly damped system with significant overshoot and ringing. Practical designs usually target 45 to 60 degrees of phase margin. A margin near zero would indicate marginal stability, with negative margin indicating instability.

Question 26Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a three-phase star-connected system with a balanced load, the line voltage is related to the phase voltage by which factor?

  1. 1/3
  2. 1/√3
  3. 3
  4. √3 Correct answer.

Explanation

In a balanced star connection the line voltage is the phasor difference of two phase voltages 120° apart, giving a magnitude of √3 times the phase voltage. The line current equals the phase current in star.

Question 27Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

Which quantity is conserved at every node of an electrical network according to Kirchhoff's current law?

  1. Power
  2. Charge Correct answer.
  3. Energy
  4. Magnetic flux

Explanation

Kirchhoff's current law expresses conservation of electric charge: the algebraic sum of currents entering a node is zero. Energy conservation underlies Kirchhoff's voltage law instead.

Question 28Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

Which binary code assigns a unique 4-bit pattern to each decimal digit 0 through 9 while leaving six patterns unused?

  1. BCD (8421) Correct answer.
  2. Gray code
  3. ASCII
  4. Excess-3 code

Explanation

Binary-coded decimal uses the first ten 4-bit combinations of the 8421 weighting for digits 0–9, leaving six invalid patterns. Gray code and excess-3 are different encodings, and ASCII is a 7-bit character code.

Question 29Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a tensile test, the ratio of stress to strain within the linear elastic region of a metal is called which property?

  1. Young's modulus Correct answer.
  2. Toughness
  3. Poisson's ratio
  4. Yield strength

Explanation

Young's modulus is the slope of the linear portion of the stress–strain curve and measures elastic stiffness. Poisson's ratio relates lateral to axial strain, yield strength marks the onset of plasticity, and toughness is energy absorbed before fracture.

Question 30Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

Which type of bearing is designed primarily to carry radial loads with minimal axial thrust capacity?

  1. Taper roller bearing
  2. Deep groove ball bearing Correct answer.
  3. Spherical roller thrust bearing
  4. Thrust ball bearing

Explanation

Deep groove ball bearings are the standard choice for radial loads, although they can accept modest axial loads. Thrust bearings are designed for axial loads, and taper rollers handle combined radial and axial loads.

Question 31Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

Which type of foundation is most suitable when a structure must transfer heavy loads through soft upper soil to a firm stratum at depth?

  1. Raft foundation
  2. Strip footing
  3. Pile foundation Correct answer.
  4. Isolated footing

Explanation

Pile foundations transmit loads through weak upper layers to a competent bearing stratum by skin friction or end bearing. Shallow footings and rafts spread loads near the surface and cannot bypass a deep soft layer.

Question 32Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

Which property of an algorithm refers to the amount of extra memory it needs beyond the input, expressed as a function of input size?

  1. Time complexity
  2. Space complexity Correct answer.
  3. Stability
  4. Determinism

Explanation

Space complexity quantifies the auxiliary memory an algorithm requires as input size grows. Time complexity measures operations executed, determinism concerns predictable outputs, and stability concerns preserving order of equal keys in sorting.

Question 33Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a DC circuit, a resistor of 100 Ω dissipates 4 W. What is the current flowing through it?

  1. 0.2 A Correct answer.
  2. 40 A
  3. 2 A
  4. 0.04 A

Explanation

Using P = I²R, I = √(P/R) = √(4/100) = √0.04 = 0.2 A. This is a direct application of the power law for a resistive element.

Question 34Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A 10 kΩ resistor and a 40 kΩ resistor are connected in parallel. What is the equivalent resistance?

  1. 50 kΩ
  2. 8 kΩ Correct answer.
  3. 4 kΩ
  4. 30 kΩ

Explanation

For two parallel resistors, Req = (R1·R2)/(R1+R2) = (10·40)/(50) = 8 kΩ. The equivalent is always smaller than the smallest branch resistance.

Question 35Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A 5 m long simply supported beam carries a uniformly distributed load of 10 kN/m over its full span. What is the maximum bending moment?

  1. 31.25 kN·m Correct answer.
  2. 62.5 kN·m
  3. 125 kN·m
  4. 15.6 kN·m

Explanation

For a simply supported beam with a uniform load, Mmax = wL²/8 = 10 × 25 / 8 = 31.25 kN·m at midspan. The reaction at each support is wL/2 = 25 kN.

Question 36Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A simply supported beam of rectangular cross-section has depth twice its width. If the width is doubled while the depth is unchanged, how does the section modulus about the horizontal axis change?

  1. It quadruples
  2. It remains unchanged
  3. It doubles Correct answer.
  4. It halves

Explanation

Section modulus Z = bd²/6, so it is directly proportional to width b for fixed depth d. Doubling b therefore doubles Z; quadrupling would require doubling the depth.

Question 37Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A 200 V DC series motor has an armature resistance of 0.5 Ω and a series field resistance of 0.3 Ω. At a certain load the current is 20 A. What is the back EMF?

  1. 184 V Correct answer.
  2. 196 V
  3. 200 V
  4. 216 V

Explanation

Back EMF Eb = V − I(Ra + Rf) = 200 − 20(0.8) = 200 − 16 = 184 V. Both the armature and series field drops must be subtracted.

Question 38Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a CMOS inverter, what is the main reason for the very low static power dissipation?

  1. Both transistors conduct heavily in steady state
  2. The threshold voltages are set to zero
  3. The gate capacitance is discharged continuously
  4. One transistor is always off in steady state, blocking the supply-to-ground path Correct answer.

Explanation

In steady state either the pull-up or pull-down network is off, so no direct path exists from VDD to ground and only leakage remains. Dynamic power arises during switching when both conduct momentarily.

Question 39Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A 4-bit binary counter is reset to 0000. After 13 clock pulses, what is its binary state?

  1. 1011
  2. 1101 Correct answer.
  3. 1110
  4. 1001

Explanation

A 4-bit counter increments modulo 16, so after 13 pulses the state equals decimal 13, which is 1101 in binary. Counting from 0000, the 13th pulse gives 1101.

Question 40Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A 16-bit instruction format uses 4 bits for the opcode and 12 bits for the address field. What is the maximum number of distinct memory addresses directly referenceable by one instruction?

  1. 256
  2. 4096 Correct answer.
  3. 16
  4. 65536

Explanation

The address field has 12 bits, so it can encode 2¹² = 4096 distinct addresses. The opcode width limits the number of operations, not the addressable locations per instruction.

Question 41Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A CPU cache has a hit rate of 90% and a main memory access time of 100 ns. If the cache access time is 10 ns and the miss penalty is the full main memory access time, what is the average memory access time?

  1. 19 ns
  2. 20 ns Correct answer.
  3. 110 ns
  4. 100 ns

Explanation

AMAT = hit time + miss rate × miss penalty = 10 + 0.10 × 100 = 20 ns. The miss penalty is added to every access weighted by the miss rate.

Question 42Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A soil has a porosity of 40%. What is its void ratio?

  1. 0.60
  2. 0.40
  3. 0.67 Correct answer.
  4. 1.50

Explanation

Void ratio e and porosity n are related by e = n/(1 − n) = 0.40/0.60 = 0.67. Void ratio expresses voids relative to solids volume, whereas porosity uses total volume.

Question 43Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A simply supported rectangular beam is to carry a given bending moment. If only the depth is doubled while width stays constant, how does the maximum bending stress change?

  1. It doubles
  2. It becomes one half
  3. It becomes one quarter Correct answer.
  4. It stays the same

Explanation

Bending stress σ = M/Z and Z = bd²/6, so σ is inversely proportional to d². Doubling depth reduces the stress to one quarter for the same moment.

Question 44Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A single-phase full-wave bridge rectifier is fed from a 230 V, 50 Hz supply and drives a resistive load. What is the approximate ripple frequency of the output voltage?

  1. 25 Hz
  2. 200 Hz
  3. 100 Hz Correct answer.
  4. 50 Hz

Explanation

A full-wave rectifier produces two output pulses per supply cycle, so the ripple frequency is 2 × 50 = 100 Hz. A half-wave rectifier would give 50 Hz.

Question 45Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A control system has a steady-state error to a step input that is finite and nonzero. Which system type does this indicate?

  1. Type 0 Correct answer.
  2. Type 1
  3. Type 3
  4. Type 2

Explanation

A type 0 system has no integrator in the forward path, so it exhibits a finite steady-state step error of 1/(1+Kp). Type 1 and higher systems have zero steady-state error to a step.

Question 46Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A steel rod of length 2 m and cross-sectional area 500 mm² is subjected to an axial tensile force of 50 kN. Taking E = 200 GPa, what is the elongation?

  1. 0.5 mm
  2. 0.1 mm
  3. 2.0 mm
  4. 1.0 mm Correct answer.

Explanation

Elongation δ = FL/(AE) = (50×10³ × 2)/(500×10⁻⁶ × 200×10⁹) = 100×10³ / 100×10⁶ = 1.0 mm. Consistent SI units are essential.

Question 47Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A pipeline carries water at 2 m/s through a section of 100 mm diameter that suddenly reduces to 50 mm diameter. Applying continuity, what is the velocity in the smaller section?

  1. 4 m/s
  2. 8 m/s Correct answer.
  3. 2 m/s
  4. 16 m/s

Explanation

Continuity gives A1V1 = A2V2, and area scales with diameter squared. Halving the diameter quarters the area, so velocity increases fourfold to 8 m/s.

Question 48Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

In a virtual memory system, a translation lookaside buffer (TLB) is used primarily to do which of the following?

  1. Hold the page replacement policy counters
  2. Cache recent virtual-to-physical address translations Correct answer.
  3. Provide non-volatile storage for the page table
  4. Store the contents of recently accessed data words

Explanation

The TLB is a small associative cache of page table entries that avoids a full page-table walk for most accesses. It stores translations, not data, and is volatile.

Question 49Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A 3-phase, 400 V, 50 Hz induction motor has a synchronous speed of 1500 rpm. At a certain load the rotor frequency is measured as 2 Hz. What is the rotor speed?

  1. 1380 rpm
  2. 1560 rpm
  3. 1500 rpm
  4. 1440 rpm Correct answer.

Explanation

Slip s = fr/fs = 2/50 = 0.04, so rotor speed N = Ns(1 − s) = 1500 × 0.96 = 1440 rpm. Rotor frequency equals slip times supply frequency.

Question 50Technical Discipline - Core Engineering (Electronics / Mechanical / Computer Science / Civil, as applicable)

A discrete-time LTI system has the transfer function H(z) = 1/(1 − 0.5z⁻¹). For what region of convergence is the system stable and causal?

  1. The entire z-plane
  2. |z| < 0.5
  3. |z| > 0.5 Correct answer.
  4. 0.5 < |z| < 1

Explanation

The pole is at z = 0.5. Causality requires the ROC to be outside the pole radius, and stability requires it to include the unit circle; |z| > 0.5 satisfies both.