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RVUNL JE practice questions

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Question 1Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 3-phase, 50 Hz induction motor runs at 1440 rpm. What is the percentage slip?

  1. 4% Correct answer.
  2. 5%
  3. 3%
  4. 2.4%

Explanation

Synchronous speed for a 4-pole machine at 50 Hz is 120f/p = 1500 rpm. Slip equals (1500 − 1440)/1500, which is 0.04 or 4 percent. Slip is always expressed relative to synchronous speed, not rotor speed.

Question 2Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a star-connected balanced load supplied from a 400 V three-phase line, the phase voltage across each element is approximately:

  1. 400 V
  2. 231 V Correct answer.
  3. 133 V
  4. 692 V

Explanation

For a star connection the phase voltage equals the line voltage divided by the square root of three. Dividing 400 V by 1.732 gives about 231 V per phase. Line current equals phase current in a star connection.

Question 3Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The primary purpose of a Buchholz relay in an oil-immersed power transformer is to:

  1. Detect incipient faults by sensing gas accumulation Correct answer.
  2. Regulate the secondary voltage under load
  3. Improve the power factor of the transformer
  4. Limit the magnetising inrush current

Explanation

A Buchholz relay is mounted in the pipe between the transformer tank and the conservator. It collects gas produced by incipient faults such as arcing or overheating and trips the breaker on severe faults. It is a protective device, not a control or compensation device.

Question 4Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

Which material is most commonly used for the core of a power transformer because of its high permeability and low hysteresis loss?

  1. Aluminium
  2. Cold-rolled grain-oriented silicon steel Correct answer.
  3. Cast iron
  4. Copper

Explanation

Cold-rolled grain-oriented silicon steel has low hysteresis loss and high permeability along the rolling direction. The silicon addition raises resistivity and reduces eddy current loss. Copper and aluminium are conductor materials, not core materials.

Question 5Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a first-angle orthographic projection, the view placed below the front view represents the:

  1. Bottom view
  2. Top view Correct answer.
  3. Left side view
  4. Right side view

Explanation

In first-angle projection the object is imagined between the observer and the plane, so the top view is projected below the front view. The left side view appears on the right of the front view. This is the reverse of third-angle placement.

Question 6Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The unit of dynamic viscosity in the SI system is:

  1. kg/m³
  2. N·s/m² Correct answer.
  3. N/m
  4. m²/s

Explanation

Dynamic viscosity relates shear stress to velocity gradient, giving units of pascal-second, which equals N·s/m². Kinematic viscosity, obtained by dividing by density, has units of m²/s. Density has units of kg/m³ and surface tension N/m.

Question 7Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a simply supported beam carrying a central point load W over span L, the maximum bending moment is:

  1. WL/4 Correct answer.
  2. WL/8
  3. WL/2
  4. WL²/8

Explanation

The reactions at each support are W/2, and the maximum moment occurs at mid-span. It equals the reaction multiplied by half the span, giving WL/4. The expression WL²/8 applies to a uniformly distributed load, not a central point load.

Question 8Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a C program, which operator has the highest precedence among the following?

  1. Relational less-than (<)
  2. Postfix increment (++) Correct answer.
  3. Logical AND (&&)
  4. Assignment (=)

Explanation

Postfix increment binds tighter than arithmetic, relational, logical and assignment operators. Relational operators rank above logical AND, and assignment has nearly the lowest precedence. Therefore the postfix increment is evaluated first in a mixed expression.

Question 9Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 100 Ω resistor carries a current of 0.5 A. The power dissipated in the resistor is:

  1. 12.5 W
  2. 100 W
  3. 25 W Correct answer.
  4. 50 W

Explanation

Power in a resistor equals current squared times resistance, so 0.5² × 100 = 25 W. Alternatively, the voltage drop is 50 V and power is V × I = 25 W. Both methods give the same result.

Question 10Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The synchronous speed of a 6-pole induction motor supplied at 50 Hz is:

  1. 1000 rpm Correct answer.
  2. 1500 rpm
  3. 3000 rpm
  4. 750 rpm

Explanation

Synchronous speed is given by 120f/p, where f is supply frequency and p is pole number. Substituting 120 × 50 / 6 yields 1000 rpm. The rotor always runs slightly below this value under motoring conditions.

Question 11Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a DC shunt generator, the voltage build-up at no load fails to start most commonly because:

  1. The load current is excessive
  2. The commutator has too many segments
  3. The field resistance is above the critical value Correct answer.
  4. The armature resistance is too low

Explanation

A shunt generator builds voltage only if the field circuit resistance line intersects the magnetisation curve. If field resistance exceeds the critical resistance, no stable voltage builds up. Residual magnetism and correct field polarity are also prerequisites.

Question 12Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 50 kVA transformer has iron loss of 500 W and full-load copper loss of 1000 W. At what fraction of full load does maximum efficiency occur?

  1. 0.707 Correct answer.
  2. 0.25
  3. 0.5
  4. 1.0

Explanation

Maximum efficiency occurs when copper loss equals iron loss. Since copper loss varies with the square of load fraction, x² × 1000 = 500, giving x = 0.707. The transformer therefore peaks in efficiency at about 70.7 percent of rated load.

Question 13Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a 3-phase squirrel cage induction motor, the starting torque can be improved by using:

  1. A larger cooling fan
  2. Fewer stator slots
  3. A thinner shaft
  4. A deep bar or double cage rotor Correct answer.

Explanation

Deep bar and double cage rotors exploit skin effect at starting, raising rotor resistance and hence starting torque while keeping running resistance low. This gives good starting performance without external rotor resistance. Shaft thickness, slot count and cooling do not directly improve starting torque.

Question 14Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A wattmeter reads the power in a circuit where voltage is 230 V and current is 10 A at a power factor of 0.8 lagging. The reading is:

  1. 1150 W
  2. 2875 W
  3. 2300 W
  4. 1840 W Correct answer.

Explanation

Active power equals V × I × cos φ, so 230 × 10 × 0.8 = 1840 W. The product V × I alone gives apparent power in volt-amperes, not watts. The power factor reduces the active component.

Question 15Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a BJT common-emitter amplifier, the purpose of emitter bypass capacitor is to:

  1. Reduce the collector supply voltage
  2. Increase the DC bias current
  3. Protect the transistor from reverse breakdown
  4. Provide AC gain by bypassing the emitter resistor Correct answer.

Explanation

The emitter resistor provides DC bias stability through negative feedback. Bypassing it with a capacitor gives a low-impedance path for AC, so AC gain rises while DC operating point remains stable. This separates DC bias from AC signal behaviour.

Question 16Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 4-bit successive approximation ADC has a full-scale reference of 5 V. The resolution of the converter is approximately:

  1. 5 V
  2. 0.625 V
  3. 1.25 V
  4. 0.3125 V Correct answer.

Explanation

Resolution equals full-scale voltage divided by 2 raised to the number of bits. For 4 bits this is 5/16, which is 0.3125 V. More bits reduce the step size and improve resolution.

Question 17Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a hydroelectric plant, the function of a surge tank is to:

  1. Absorb pressure surges in the penstock Correct answer.
  2. Step up the generator voltage
  3. Increase the head at the turbine
  4. Filter debris from the water

Explanation

A surge tank is located between the reservoir and the turbine to absorb rapid pressure changes caused by load rejection or sudden valve closure. It protects the penstock from water hammer and improves transient stability of the water column. It does not alter head or filter water.

Question 18Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a vapour compression refrigeration cycle, the component that rejects heat to the surroundings is the:

  1. Condenser Correct answer.
  2. Expansion valve
  3. Compressor
  4. Evaporator

Explanation

The condenser rejects latent heat from the high-pressure refrigerant vapour to the ambient medium. The evaporator absorbs heat from the refrigerated space, while the compressor raises pressure and the expansion valve drops it. Heat rejection and absorption occur at different components.

Question 19Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A shaft transmits 15 kW at 1500 rpm. The torque transmitted is approximately:

  1. 225 N·m
  2. 95.5 N·m Correct answer.
  3. 15 N·m
  4. 10 N·m

Explanation

Power equals torque times angular velocity, so torque is P/ω. Angular velocity is 2π × 1500/60 = 157 rad/s, giving 15000/157 ≈ 95.5 N·m. Speed must be converted from rpm to radians per second.

Question 20Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a simply supported beam of span 6 m with a uniformly distributed load of 10 kN/m over the whole span, the maximum shear force is:

  1. 10 kN
  2. 15 kN
  3. 60 kN
  4. 30 kN Correct answer.

Explanation

Total load is 10 kN/m × 6 m = 60 kN, shared equally by the two supports. Each reaction is 30 kN, which is also the maximum shear force at the supports. Shear force reduces linearly to zero at mid-span.

Question 21Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The workability of concrete is commonly measured by the:

  1. Sieve analysis
  2. Soundness test
  3. Slump test Correct answer.
  4. Compression test

Explanation

The slump test measures the consistency and workability of fresh concrete. Compression tests measure hardened strength, sieve analysis characterises aggregates, and soundness tests check cement expansion. Workability must be assessed on fresh concrete.

Question 22Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a 3-phase transmission line, the effect of transposition of conductors is to:

  1. Reduce the conductor weight
  2. Equalise the inductance and capacitance of the three phases Correct answer.
  3. Eliminate corona discharge completely
  4. Increase the line voltage

Explanation

Transposition rotates the physical positions of the three conductors at regular intervals along the line. This balances the flux linkages and capacitances so each phase sees the same average inductance and capacitance. It reduces voltage unbalance over long lines.

Question 23Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 100 MVA generator with 20% subtransient reactance is connected to a system with a 100 MVA base. The per-unit subtransient reactance on a 200 MVA base is:

  1. 0.1 pu
  2. 0.8 pu
  3. 0.2 pu
  4. 0.4 pu Correct answer.

Explanation

Per-unit reactance scales in proportion to the new base MVA divided by the old base MVA. Hence 0.2 × (200/100) = 0.4 pu. Base voltage changes would also enter the formula, but the voltage base is unchanged here.

Question 24Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a 3-phase full-wave bridge rectifier fed from a 400 V line, the average DC output voltage with resistive load is approximately:

  1. 180 V
  2. 400 V
  3. 540 V Correct answer.
  4. 270 V

Explanation

For a 3-phase full bridge, average output is 1.35 times the line-to-line RMS voltage. Multiplying 1.35 by 400 V gives about 540 V. This factor arises from integrating the six-pulse waveform over a 60-degree interval.

Question 25Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 3-phase induction motor draws a starting current of six times full-load current and develops a starting torque of 1.5 times full-load torque. If a star-delta starter is used, the starting torque becomes:

  1. 3.0 times full-load torque
  2. 1.5 times full-load torque
  3. 0.5 times full-load torque Correct answer.
  4. 0.75 times full-load torque

Explanation

Star-delta starting reduces the voltage across each phase winding to 1/√3 of the delta value. Since torque varies with the square of voltage, the starting torque falls to one-third of the direct-on-line value. One-third of 1.5 gives 0.5 times full-load torque.

Question 26Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

For a single-phase transformer supplying a purely resistive load, the primary current waveform under steady sinusoidal excitation is essentially:

  1. Sinusoidal and in phase with the applied voltage Correct answer.
  2. A peaked non-sinusoidal wave rich in third harmonics
  3. A square wave alternating between two fixed values
  4. Sinusoidal but lagging the voltage by 90°

Explanation

With a resistive burden the secondary current is sinusoidal and in phase with secondary voltage, so the load component of primary current reflected through the turns ratio is also sinusoidal and in phase with the supply. Only the small magnetising component is non-sinusoidal, and it is negligible compared with the load current at rated load.

Question 27Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a separately excited DC motor, the back EMF at rated armature voltage is 220 V when running at 1000 rpm. If the flux is held constant and the load torque is reduced so that the armature current halves while the speed rises to 1100 rpm, the new back EMF is approximately:

  1. 198 V
  2. 242 V Correct answer.
  3. 200 V
  4. 220 V

Explanation

Back EMF is proportional to flux and speed, so E = k·φ·N. With flux constant, E scales directly with speed: 220 × (1100/1000) = 242 V. Armature current affects the terminal voltage drop across armature resistance, not the back EMF relationship itself.

Question 28Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The strain energy stored in a uniform bar of length L, cross-sectional area A and Young's modulus E, subjected to a gradually applied axial tensile load P, is:

  1. P²L / (2AE) Correct answer.
  2. P L² / (2AE)
  3. P²L / (AE)
  4. PL / (AE)

Explanation

For an axially loaded bar the strain energy is the integral of (P²/(2AE))dx over the length, giving P²L/(2AE). The factor 2 arises because the load builds up gradually from zero to P, so the average force does half the work of the full load.

Question 29Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A simply supported rectangular beam of width 150 mm and depth 300 mm carries a maximum bending moment of 27 kN·m. The maximum bending stress developed in the section is:

  1. 12 N/mm² Correct answer.
  2. 24 N/mm²
  3. 3 N/mm²
  4. 6 N/mm²

Explanation

Section modulus Z = bd²/6 = 150 × 300²/6 = 2.25 × 10⁶ mm³. Bending stress σ = M/Z = 27 × 10⁶ / 2.25 × 10⁶ = 12 N/mm². The depth enters squared, which is why the stress is far below the concrete or steel yield values for this moment.

Question 30Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a 3-phase, 415 V, 50 Hz star-connected system, the phase voltage available across each winding is approximately:

  1. 180 V
  2. 415 V
  3. 720 V
  4. 240 V Correct answer.

Explanation

In a star connection the line voltage is √3 times the phase voltage, so the phase voltage is 415/√3 ≈ 240 V. This is the reason domestic single-phase supply in India is derived from one phase of a 415 V star system.

Question 31Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 3-phase, 400 V, 50 Hz, 4-pole induction motor runs at a slip of 4%. The rotor frequency is:

  1. 50 Hz
  2. 2 Hz Correct answer.
  3. 4 Hz
  4. 0.5 Hz

Explanation

Rotor frequency equals slip times supply frequency, f_r = s·f = 0.04 × 50 = 2 Hz. This low rotor frequency is why rotor iron loss in a normally running induction motor is small and core loss is usually taken on the stator side.

Question 32Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a power system, the purpose of a current transformer burden rating is to specify:

  1. The maximum volt-ampere loading the secondary can supply while meeting its accuracy class Correct answer.
  2. The maximum primary current the CT can carry without saturation
  3. The insulation level of the primary winding to earth
  4. The ratio of secondary turns to primary turns

Explanation

The burden is the total impedance of the secondary circuit, including relays, meters and leads, expressed in VA at rated secondary current. Exceeding it drives the core towards saturation and degrades ratio and phase-angle accuracy.

Question 33Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The main function of a Buchholz relay in an oil-immersed transformer is to:

  1. Provide cooling by circulating oil through radiators
  2. Regulate the secondary voltage under varying load
  3. Limit the fault current flowing through the transformer winding
  4. Detect incipient faults by sensing gas generated by decomposition of oil Correct answer.

Explanation

The Buchholz relay sits in the pipe between the tank and the conservator and collects gas produced by arcing or local overheating. A slow accumulation of gas triggers an alarm, whereas a violent surge of oil trips the breaker.

Question 34Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 3-phase, 50 Hz, 6-pole slip-ring induction motor has a rotor resistance of 0.02 Ω per phase and standstill rotor reactance of 0.1 Ω per phase. The slip at which maximum torque occurs is:

  1. 0.02
  2. 0.5
  3. 0.1
  4. 0.2 Correct answer.

Explanation

Maximum torque in an induction motor occurs at the slip where rotor resistance equals rotor leakage reactance, that is s_m = R₂/X₂. Here 0.02/0.1 = 0.2, so peak torque is developed at 20% slip. Adding external rotor resistance raises this slip and can be used to shift peak torque towards standstill for starting.

Question 35Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a common-emitter amplifier, the output voltage is 180° out of phase with the input because:

  1. An increase in base current raises collector current and hence increases the drop across the collector resistor Correct answer.
  2. The coupling capacitor at the output shifts the phase by half a cycle
  3. The emitter degeneration resistor introduces a phase shift
  4. The transistor inverts the signal by capacitive coupling at the input

Explanation

In a CE stage the collector resistor converts the collector current into a voltage that falls as current rises. Since base current and collector current rise together with a positive input swing, the collector voltage moves opposite to the input, giving the 180° inversion.

Question 36Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The output of a 12-bit digital-to-analogue converter with a full-scale output of 10 V, when the input code is 100000000000, is approximately:

  1. 5.00 V Correct answer.
  2. 0.0024 V
  3. 10.00 V
  4. 2.50 V

Explanation

A 12-bit converter has 4096 steps, and the code 100000000000 is the mid-scale value 2048. The output is therefore 2048 × (10/4096) = 5.00 V, exactly half of full scale.

Question 37Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a microprocessor-based system, the main reason for using memory-mapped I/O rather than isolated I/O is that:

  1. It eliminates the need for an interrupt controller
  2. It requires fewer address lines on the bus
  3. It allows peripherals to be accessed without a chip-select decoder
  4. All memory-reference instructions can be used to access peripheral registers Correct answer.

Explanation

Memory-mapped I/O places peripheral registers in the same address space as memory, so the full instruction set, including arithmetic and logical operations, can act directly on them. The trade-off is that it consumes part of the memory address space.

Question 38Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a vapour compression refrigeration system, the function of the expansion valve is to:

  1. Compress the refrigerant from evaporator pressure to condenser pressure
  2. Increase the enthalpy of the refrigerant before it enters the compressor
  3. Reduce the refrigerant pressure from condenser level to evaporator level Correct answer.
  4. Remove moisture from the refrigerant before it enters the evaporator

Explanation

The expansion device throttles the refrigerant from the high condenser pressure to the low evaporator pressure, which also drops its temperature so that it can absorb heat in the evaporator. In an ideal cycle this throttling is isenthalpic.

Question 39Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A Pelton wheel is supplied with water at a net head of 100 m. The theoretical jet velocity, neglecting nozzle losses, is approximately:

  1. 44.3 m/s Correct answer.
  2. 9.8 m/s
  3. 98 m/s
  4. 19.8 m/s

Explanation

Jet velocity follows from the energy equation, V = √(2gH) = √(2 × 9.81 × 100) ≈ 44.3 m/s. The Pelton runner is then designed so that bucket speed is about half the jet speed for maximum hydraulic efficiency.

Question 40Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The main reason for providing a volute casing around a centrifugal pump impeller is to:

  1. Convert the high velocity of the water leaving the impeller into pressure gradually Correct answer.
  2. Increase the speed of the impeller without cavitation
  3. Prevent axial thrust by balancing the pressure on both sides
  4. Filter out suspended solids before the water enters the impeller

Explanation

The gradually increasing flow area of the volute diffuses the high-velocity discharge from the impeller, converting kinetic energy into pressure energy. A diffuser ring of guide vanes performs the same duty in a turbine pump.

Question 41Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A mild steel specimen tested in tension shows a yield stress of 250 N/mm² and an ultimate tensile strength of 400 N/mm². The factor of safety with respect to yield, for a design working stress of 125 N/mm², is:

  1. 3.2
  2. 1.6
  3. 0.5
  4. 2.0 Correct answer.

Explanation

Factor of safety on yield is the yield stress divided by the permissible working stress: 250/125 = 2.0. Using ultimate strength instead would give 400/125 = 3.2, which is a different design basis.

Question 42Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In concrete technology, the slump cone test is performed to assess:

  1. Consistency and workability of fresh concrete Correct answer.
  2. Bond strength between concrete and reinforcement
  3. Permeability of hardened concrete
  4. Compressive strength of hardened concrete

Explanation

The slump test measures the vertical settlement of fresh concrete under its own weight, giving an indication of consistency and workability. It is a fresh-state test and says nothing directly about hardened properties.

Question 43Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a plane table survey, the method of resection is used to:

  1. Establish a baseline between two known stations
  2. Determine the elevation of points by trigonometric levelling
  3. Locate the position of the instrument station by sighting known points Correct answer.
  4. Plot the positions of objects by radiating rays from a single setup

Explanation

Resection fixes the plan position of the plane table station itself by observing at least three well-defined points whose positions are already plotted, using the three-point problem. It is useful when the table must be set up at an unknown point.

Question 44Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A trapezoidal channel has a bottom width of 4 m, side slopes of 1:1 (horizontal:vertical) and a flow depth of 1.5 m. The wetted perimeter is:

  1. 7.00 m
  2. 8.24 m Correct answer.
  3. 10.00 m
  4. 5.50 m

Explanation

For a trapezoid the wetted perimeter is b + 2y√(1 + z²), where z is the horizontal side slope. Here 4 + 2 × 1.5 × √2 = 4 + 4.24 = 8.24 m. The area, by contrast, is y(b + zy) = 1.5 × 5.5 = 8.25 m².

Question 45Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

The pH value of a water sample is 9.0. The concentration of hydrogen ions in the sample is:

  1. 10⁻⁵ mol/L
  2. 9 mol/L
  3. 10⁹ mol/L
  4. 10⁻⁹ mol/L Correct answer.

Explanation

pH is defined as the negative logarithm to base ten of the hydrogen ion activity, so [H⁺] = 10^(−pH) = 10⁻⁹ mol/L. A value of 9 indicates an alkaline sample, since neutral water at 25 °C has pH 7.

Question 46Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In an instrumentation system, the term 'span' of a pressure transmitter with a range of 0 to 250 kPa refers to:

  1. The accuracy expressed as a percentage of full scale
  2. The algebraic difference between the upper and lower range limits, 250 kPa Correct answer.
  3. The maximum pressure the sensor can withstand without damage
  4. The lower range value of 0 kPa

Explanation

Span is the algebraic difference between the upper and lower calibrated range limits, so for 0 to 250 kPa the span is 250 kPa. It is distinct from zero, which is the lower range value, and from the over-range or proof pressure.

Question 47Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A platinum resistance thermometer is preferred over a thermocouple for precise industrial temperature measurement mainly because it:

  1. Requires no excitation current
  2. Responds faster than any thermocouple
  3. Produces a larger output voltage than any thermocouple
  4. Has high stability and a nearly linear resistance-temperature relationship over a wide range Correct answer.

Explanation

Platinum is chemically stable and its resistance varies with temperature in a well-characterised, nearly linear manner, which makes Pt100 sensors highly repeatable. Thermocouples are cheaper and cover higher temperatures but need cold-junction compensation and drift more.

Question 48Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a programmable logic controller, a scan cycle consists of:

  1. Only the execution of the ladder program
  2. Input reading, program execution and output updating, repeated continuously Correct answer.
  3. Program compilation followed by a single output update
  4. Communication with the programming terminal followed by a memory reset

Explanation

The PLC reads all input modules into the process image, executes the user program from top to bottom, then writes the results to the output modules. This repeated cycle means the response time of a PLC depends on the total scan time.

Question 49Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

A 3-phase, 11 kV feeder has a per-phase series reactance of 4 Ω and carries a load current of 200 A at 0.8 power factor lagging. The per-phase voltage drop due to the reactance alone is approximately:

  1. 320 V
  2. 640 V
  3. 800 V
  4. 480 V Correct answer.

Explanation

For a lagging load the reactive voltage drop is I·X·sin φ, and sin φ = 0.6 when the power factor is 0.8. Hence the drop is 200 × 4 × 0.6 = 480 V per phase. The resistive term, if present, would add I·R·cos φ to this value.

Question 50Engineering Discipline - Technical Knowledge (post-specific: Electrical / Mechanical / Civil / Instrumentation / Electronics / IT & other advertised branches)

In a 3-phase system, the per-unit quantity that is the same on both sides of an ideal transformer when base voltages are chosen in proportion to the turns ratio is:

  1. Base current
  2. Base impedance
  3. Per-unit impedance Correct answer.
  4. Actual ohmic impedance

Explanation

Choosing base voltages in the turns-ratio proportion makes the per-unit impedance continuous across an ideal transformer, so the transformer can be omitted from the per-unit equivalent circuit. Base impedance and base current, by contrast, change from one side to the other.