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Past Questions
Transformer tank is not filled with water because
A)
it has bad cooling property but good insulating property
B)
it has bad cooling and bad insulating property
C)
it has good cooling property but bad insulating property
D)
none of above
In a transformer, the medium inside the tank serves two primary purposes: cooling the core and windings, and providing electrical insulation between the high-voltage components and the grounded tank.
1. **Cooling Property**: Water has a very high specific heat capacity and thermal conductivity, making it an excellent cooling medium (better than transformer oil). Therefore, it has 'good cooling properties'.
2. **Insulating Property**: Pure water is a poor conductor, but in practical applications, water easily absorbs impurities and ions, making it highly conductive. More importantly, it cannot provide the high dielectric strength required to prevent electrical arcing/breakdown between the windings and the tank. Therefore, it has 'bad insulating properties'.
Because a transformer requires a medium that can both cool and insulate, transformer oil is used instead of water, as oil provides the necessary dielectric strength (insulation) while still offering adequate cooling. Thus, water is not used because while it cools well, it fails as an insulator.
Efficiency of a power transformer is of the order of-
A)
75%
B)
50%
C)
98%
D)
100%
A power transformer is highly efficient because it has no moving parts and its losses are relatively small (mainly copper loss and core/iron loss). In practice, large power transformers commonly achieve efficiencies around 98% or even slightly higher, so 98% is the correct order of efficiency.
Why the others are incorrect:
- 100% is impossible because some power is always lost as heat in windings and core.
- 75% is far too low for a transformer; that would indicate excessive losses.
- 50% is completely unrealistic for a power transformer and is far below normal operating efficiency.
Standard frequency of supply in India is-
A)
25Hz
B)
100 Hz
C)
50 Hz
D)
none of above
The standard frequency of the Alternating Current (AC) power supply in India is 50 Hz (Hertz). This means that the current changes its direction 50 times per second. This standard was adopted during the British era and is consistent with the power grid standards used across most of Europe and Asia.
Analysis of options:
- Option (a) 25Hz: This is an obsolete frequency used in some early railway systems but is not the national standard.
- Option (b) 100 Hz: This is not a standard utility frequency for power distribution.
- Option (c) 50 Hz: This is the correct national standard for India.
- Option (d) none of above: Incorrect, as option (c) is correct.
In two W meter method, if the power factor is unity, then,
A)
W1 > W2
B)
W1 < W2
C)
W1 = W2
D)
none of above
In the two-wattmeter method for measuring three-phase power, the readings of the two wattmeters (W1 and W2) are given by the formulas: W1 = V_L I_L cos(30° + φ) and W2 = V_L I_L cos(30° - φ), where φ is the phase angle of the load.
1. When the power factor is unity (cos φ = 1), the phase angle φ = 0°.
2. Substituting φ = 0° into the formulas:
W1 = V_L I_L cos(30° + 0°) = V_L I_L cos(30°)
W2 = V_L I_L cos(30° - 0°) = V_L I_L cos(30°)
3. Therefore, W1 = W2.
Additional context for other options:
- If the power factor is between 0.5 and 1, both W1 and W2 are positive, but not necessarily equal.
- If the power factor is 0.5, one wattmeter reads zero (W2 = 0).
- If the power factor is less than 0.5, one wattmeter will give a negative reading.
In electrical instruments, electrical energy is converted to-
A)
light energy
B)
mechanical energy
C)
chemical energy
D)
heat energy
Electrical measuring instruments (such as ammeters, voltmeters, and wattmeters) are designed to provide a visual reading of an electrical quantity. To achieve this, the electrical energy from the circuit being measured is converted into mechanical energy (displacement). This process typically involves three torques: the deflecting torque (which moves the pointer), the controlling torque (which opposes the deflection to ensure a linear scale), and the damping torque (which prevents oscillation). For example, in a Permanent Magnet Moving Coil (PMMC) instrument, the interaction between the magnetic field and the current-carrying coil produces a mechanical force that rotates the pointer across a scale. While heat energy (option d) is often a byproduct (I²R loss), it is not the intended conversion for the purpose of measurement in standard electrical instruments.
Ohm’s law states that (Where ‘I’ is current in ampere, ‘V’ is voltage in volts and ‘R’ is resistance in Ohm)
A)
I=V.R
B)
V=I.R
C)
R=V.I
D)
none of above
Ohm's Law is a fundamental principle in electrical engineering which states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points, provided all physical conditions (like temperature) remain constant. Mathematically, this relationship is expressed as V = I × R, where V is the potential difference in Volts, I is the current in Amperes, and R is the resistance in Ohms.
Evaluating the options:
- Option (a) I=V.R is incorrect; the correct formula for current is I = V/R.
- Option (b) V=I.R is correct as it represents the standard mathematical form of Ohm's Law.
- Option (c) R=V.I is incorrect; the correct formula for resistance is R = V/I.
The main function of power transformer is
A)
to increase or decrease the d.c. voltage
B)
to increase or decrease the a.c. voltage
C)
to convert a.c. to d.c. vice-versa
D)
none of all
A power transformer is a static electrical device that operates on the principle of Faraday's Law of Electromagnetic Induction. Its primary purpose is to change the voltage level of an alternating current (AC) supply. Depending on the turns ratio of the primary and secondary windings, it can either increase the voltage (Step-up transformer) for efficient long-distance transmission or decrease the voltage (Step-down transformer) for safe distribution and utilization by consumers.
Analysis of other options:
- Option (a) is incorrect because transformers do not work with direct current (DC). DC does not create the changing magnetic flux required to induce a voltage in the secondary winding.
- Option (c) is incorrect because the conversion of AC to DC (or vice-versa) is the function of a Rectifier or an Inverter, not a transformer.
- Option (d) is incorrect as option (b) accurately describes the function.
Voltage drop allowed in the wiring from consumer’s board at any point inside the house should be
A)
2% of declared supply voltage plus one volt
B)
3% of declared supply voltage plus one volt
C)
4% of declared supply voltage plus one volt
D)
none of above
According to standard electrical installation guidelines and the Central Electricity Authority (CEA) regulations (which govern electrical standards in India), the permissible voltage drop from the consumer's distribution board to any point in the internal wiring of a residential or commercial building is limited to ensure the efficient operation of electrical appliances. The standard limit is defined as 3% of the declared supply voltage plus one volt. This margin accounts for the inherent resistance of the conductors and ensures that the voltage at the furthest point of the installation remains within the acceptable operating range of the equipment. Option (a) is too restrictive, and Option (c) exceeds the standard safety and efficiency limits.
The maximum permissible voltage drop from supply terminals to any point in the installation for power wiring is
A)
7.5%
B)
5%
C)
4%
D)
none of above
According to standard electrical installation codes (such as the National Electrical Code and the Indian Standard IS 732), the maximum permissible voltage drop from the point of supply (supply terminals) to any point in the installation is generally limited to ensure the efficient operation of electrical equipment. For power wiring and general installations, the standard limit is 5%. A voltage drop exceeding this limit can lead to overheating of conductors, malfunction of electronic equipment, and reduced efficiency of motors (causing them to draw more current and potentially overheat). Therefore, option (b) 5% is the correct technical standard.
According to I.E. rules, the voltage fluctuation in residential buildings should not be more than
A)
2% of declared supply voltage for residential building
B)
3% of declared supply voltage for residential building
C)
6% of declared supply voltage for residential building
D)
none of above
According to the Indian Electricity (I.E.) Rules and the standards set by the Central Electricity Authority (CEA) regarding the quality of supply, the permissible variation in voltage for low-voltage (LV) supply to consumers is generally maintained within a specific tolerance band. For residential buildings and general domestic consumers, the standard permissible voltage fluctuation is ±6% of the declared nominal supply voltage. This ensures that electrical appliances operate efficiently without risking damage due to under-voltage or over-voltage conditions. Options a (2%) and b (3%) are too stringent and are typically not the standard for general residential distribution, while 6% is the industry and regulatory benchmark for these installations.
Continuity of an electrical circuit is usually checked by –
A)
ammeter
B)
voltmeter
C)
ohm meter
D)
all of the above
Continuity testing is the process of verifying whether an electrical path is complete (closed) or broken (open).
1. **Why Ohm meter is correct**: An ohmmeter measures electrical resistance. In a continuity test, the meter sends a small current through the circuit; if the resistance is very low (close to zero), it indicates a continuous path. Most modern digital multimeters have a dedicated 'continuity' setting that uses the ohmmeter function to trigger a beep when a low-resistance path is detected.
2. **Why Ammeter is incorrect**: An ammeter measures the flow of current in a live circuit. While current flow implies continuity, an ammeter is not used as a standalone tool to 'check' continuity because it requires an external power source and would be dangerous or impractical for simple path verification.
3. **Why Voltmeter is incorrect**: A voltmeter measures the potential difference between two points. While a voltage drop across a break in a circuit can indicate a lack of continuity, it is not the standard instrument used to check for a complete path.
Therefore, the ohmmeter is the specific instrument designed to measure the resistance necessary to determine continuity.
The bond strength of steel and concrete is enhanced by various measures. Which of the following do not enhance bond strength?
A)
Deformed bars are used instead of Plain bars
B)
Bigger bar diameters are used
C)
Higher grade of concrete is used
D)
Increased cover is provided.
Bond strength refers to the grip between the reinforcing steel and the surrounding concrete, which prevents slippage.
1. **Option (a) Deformed bars**: These have ribs or lugs that provide mechanical interlocking with the concrete, significantly increasing bond strength compared to smooth plain bars. Thus, this enhances bond.
2. **Option (b) Bigger bar diameters**: Bond strength is inversely proportional to the bar diameter for a given volume of concrete. As the diameter increases, the surface area per unit volume of steel decreases, and the stress concentration around the bar increases, which generally reduces the bond efficiency (bond stress). Therefore, using bigger bars does NOT enhance bond strength.
3. **Option (c) Higher grade of concrete**: A higher grade of concrete has higher compressive and tensile strength, which increases the frictional resistance and the gripping force exerted on the bar. Thus, this enhances bond.
4. **Option (d) Increased cover**: Providing adequate concrete cover ensures that the bar is fully encased and prevents the concrete from splitting or spalling prematurely under bond stress. While excessive cover doesn't 'increase' the chemical bond, insufficient cover leads to bond failure via splitting. In the context of standard RCC design, ensuring proper cover is a measure to maintain and enhance the effective bond length.
The desired temperature range of Bitumen when mixing is-
A)
120 degree centigrade – 130 degree centigrade
B)
110 degree centigrade – 140 degree centigrade
C)
150 degree centigrade – 177 degree centigrade
D)
160 degree centigrade – 187 degree centigrade
In Highway Engineering, the mixing temperature of bitumen is critical to ensure proper coating of the aggregates and adequate workability of the mix. Bitumen is a thermoplastic material; if the temperature is too low, it will be too viscous to coat the aggregates uniformly. If it is too high, the bitumen may undergo 'hardening' or 'burning' (oxidation), which leads to premature cracking and loss of ductility in the pavement. For standard paving grades of bitumen (such as VG-30), the typical mixing temperature range is generally between 150°C and 170°C-180°C. Option (c) 150°C – 177°C falls within the standard engineering specifications for hot-mix asphalt (HMA) production. Options (a) and (b) are too low, which would result in poor mixing and insufficient binder distribution. Option (d) is generally considered too high, risking the thermal degradation of the bitumen binder.
The desired temperature range of Bitumen when spreading at the location of laying is-
A)
121 degree centigrade – 163 degree centigrade
B)
110 degree centigrade – 140 degree centigrade
C)
150 degree centigrade – 177 degree centigrade
D)
160 degree centigrade – 187 degree centigrade
In highway engineering, specifically for the construction of Hot Mix Asphalt (HMA), bitumen must be heated to a specific temperature to reduce its viscosity, allowing it to coat the aggregates thoroughly and be compacted effectively. While the exact temperature depends on the grade of bitumen (e.g., VG-30, VG-40) and the specific mix design, the standard industry range for the mixing and laying temperature of bitumen-based hot mixes typically falls between 150°C and 177°C (approximately 300°F to 350°F).
- Option (a) and (b) are generally too low for the initial spreading/laying phase of hot mixes, which would lead to poor workability and inadequate compaction (cold spots).
- Option (d) is generally too high; overheating bitumen beyond 180°C can lead to 'burning' or oxidative hardening (aging), which makes the binder brittle and reduces the lifespan of the pavement.
- Option (c) represents the optimal window where the bitumen is fluid enough for spreading but not so hot that it undergoes rapid thermal degradation.
Causeway is one type of-
A)
Bridge
B)
Subsurface drainage
C)
Cross drainage
D)
Culvert
A causeway is a raised road across a stream or marshy area, designed to allow water to flow over the road surface during high-water periods (floods). In civil and highway engineering, any structure used to allow water to pass across a road or railway embankment is categorized as a 'Cross Drainage (CD) work'.
Reasoning for options:
- (a) Bridge: While a causeway is a crossing, it differs from a bridge because a bridge is designed to keep the traffic above the high-flood level (HFL), whereas a causeway is intentionally submerged during floods.
- (b) Subsurface drainage: This refers to systems (like perforated pipes) used to remove excess water from the soil beneath the road surface, not structures that cross a stream.
- (c) Cross drainage: This is the correct umbrella term. CD works include culverts, bridges, causeways, siphons, and aqueducts.
- (d) Culvert: A culvert is a specific type of CD work that allows water to pass *under* the road through a pipe or box. A causeway allows water to pass *over* the road.
The main three constituents of cement are-
A)
Aluminium, lime and Sulphur
B)
Lime, alumina and magnesium
C)
Lime, magnesium and manganese
D)
Lime, silica and alumina
Portland cement is manufactured by burning a mixture of calcareous (lime-bearing) and argillaceous (clay-bearing) materials. The primary chemical constituents that make up the bulk of the cement clinker are:
1. Lime (CaO): The most significant constituent, providing strength and stability.
2. Silica (SiO2): Provides strength through the formation of calcium silicates.
3. Alumina (Al2O3): Acts as a flux to lower the clinkering temperature and contributes to the setting properties.
While other elements like Iron Oxide, Magnesium Oxide, and Sulphur (added as Gypsum) are present, they are considered minor constituents.
Analysis of options:
- Option (a) is incorrect because Sulphur is a minor additive (gypsum) and Aluminium is part of Alumina, but Lime/Silica/Alumina are the primary trio.
- Option (b) is incorrect because Magnesium is a minor constituent (usually kept low to prevent unsoundness).
- Option (c) is incorrect because Manganese is only present in trace amounts.
- Option (d) is correct as it lists the three dominant oxides that form the structural basis of cement.
The aggregate impact value of aggregate to be used in wearing course of pavement is-
A)
less than or equal to 30%
B)
less than or equal to 40%
C)
less than 35%
D)
more than 25%
The Aggregate Impact Value (AIV) test is used to determine the resistance of aggregates to sudden shock or impact. In highway engineering, the wearing course is the topmost layer of the pavement and is subjected to the highest impact loads from vehicle tires. According to standard specifications (such as IRC - Indian Roads Congress), the maximum permissible Aggregate Impact Value for aggregates used in the wearing course of a pavement is 30%. A lower AIV indicates a tougher aggregate that can withstand impact without crushing.
- Option (a) is correct as it aligns with the standard limit of ≤ 30% for wearing courses.
- Option (b) is incorrect because 40% is generally the limit for lower layers (like the base course) but too high for the wearing course.
- Option (c) is incorrect as the standard limit is specifically 30%, not 35%.
- Option (d) is incorrect because a value 'more than 25%' would allow for aggregates that are too weak (e.g., 45%), which would lead to premature pavement failure.
Which of the following is not the desirable property of soil as highway material?
A)
Stability
B)
Good drainage
C)
Ease of compaction
D)
Compressibility
In highway engineering, the subgrade and base layers must be able to support heavy traffic loads without significant deformation.
1. Stability (Option a): This is a highly desirable property. The soil must be stable to prevent the pavement from shifting or failing under load.
2. Good drainage (Option b): This is desirable because water accumulation in the soil layers leads to a loss of shear strength, causing potholes and structural failure (rutting).
3. Ease of compaction (Option c): This is desirable because soil that can be easily compacted to its maximum dry density ensures a dense, strong foundation with minimal voids.
4. Compressibility (Option d): This is NOT a desirable property. High compressibility means the soil will undergo significant volume reduction (settlement) under load. This leads to uneven pavement surfaces, cracking, and overall structural failure of the highway. Therefore, low compressibility is desired, making 'Compressibility' the correct answer as the non-desirable property.
California Bearing Ratio (CBR) test is used-
A)
to evaluate the stability of soil subgrade
B)
to evaluate thickness of soil subgrade
C)
to measure moisture content of soil
D)
to evaluate bearing capacity of soil
The California Bearing Ratio (CBR) test is a penetration test used to evaluate the mechanical strength or stability of the subgrade soil and base courses used in flexible pavements. It measures the resistance of a soil sample to penetration by a standard piston compared to the resistance of a standard crushed stone material.
- Option (a) is correct because the CBR value directly indicates the stability and strength of the subgrade, which is essential for determining the required thickness of the pavement layers.
- Option (b) is incorrect because the CBR test is used to *determine* the required thickness of the pavement layers, but it does not 'evaluate the thickness' of the soil subgrade itself (which is a physical dimension).
- Option (c) is incorrect because moisture content is measured using separate tests (like the oven-drying method), although moisture content is a variable that affects the CBR result.
- Option (d) is a common point of confusion. While CBR relates to strength, 'Bearing Capacity' is a specific term usually associated with foundation engineering (e.g., Terzaghi's bearing capacity) for rigid structures, whereas CBR is specifically designed for pavement stability analysis.
Vicat’s apparatus is used for testing-
A)
Initial and Final Setting time of cement
B)
Specific gravity of cement
C)
Fineness of Cement
D)
Soundness of Cement
Vicat's apparatus is a standard instrument used in civil engineering to determine the consistency and the setting times of cement.
1. **Consistency Test**: First, the apparatus is used to find the 'Normal Consistency' of the cement paste (the amount of water required to allow a Vicat plunger to penetrate to a depth of 33-35 mm from the top).
2. **Initial Setting Time**: Using a thinner needle (1mm diameter), the time elapsed from adding water to the moment the needle stops penetrating to a depth of 5mm from the bottom is recorded.
3. **Final Setting Time**: Using a needle with an annular attachment, the time is recorded when the needle makes an impression but the attachment fails to do so.
Why other options are incorrect:
- **Specific gravity of cement** is measured using a Le Chatelier flask.
- **Fineness of Cement** is measured using a Sieve analysis or the Blaine Air Permeability apparatus.
- **Soundness of Cement** is measured using the Le Chatelier apparatus (for expansion due to lime) or an Autoclave (for expansion due to magnesia).
The Flexible pavement consist the following components-
A)
Subgrade, GSB, BM & surface course
B)
Subgrade, Sub-base, Base & Surface course
C)
Subgrade, Dry Lean concrete, WBM, Wearing course
D)
Subgrade, WBM, WMM & Concrete
A flexible pavement is designed to distribute the traffic load to the underlying soil (subgrade) through a series of layers with increasing strength. The standard structural components of a flexible pavement, from bottom to top, are:
1. **Subgrade**: The natural soil or compacted fill that serves as the foundation.
2. **Sub-base Course**: A layer of granular material (like GSB - Granular Sub-Base) that provides structural support and drainage.
3. **Base Course**: A high-quality crushed stone or stabilized layer (like WMM - Wet Mix Macadam) that distributes the load to the sub-base.
4. **Surface Course (Wearing Course)**: The top layer (usually bituminous) that provides a smooth riding surface and protects the lower layers from water penetration.
Analysis of other options:
- Option (a) lists specific materials (GSB, BM) rather than the general structural components.
- Option (c) includes 'Dry Lean Concrete', which is typically a component of Rigid Pavements (as a sub-base).
- Option (d) includes 'Concrete', which is the primary material for Rigid Pavements, not Flexible Pavements.
What is the number of bricks taken in analysis of cost for 1sqm half brick wall?
A)
49.5 nos
B)
52 nos
C)
52.5 nos
D)
56.5nos
To calculate the number of bricks for 1 sqm of a half-brick wall, we use the standard modular brick size and mortar joints.
1. **Standard Modular Brick Size**: The standard size of a modular brick is 190 mm x 90 mm x 90 mm.
2. **Size with Mortar**: Adding a standard mortar joint of 10 mm to the length and height, the effective size of one brick in the wall becomes 200 mm x 100 mm (0.2 m x 0.1 m).
3. **Calculation for 1 sqm**:
- Area of one brick with mortar = 0.2 m × 0.1 m = 0.02 sqm.
- Number of bricks = Total Area / Area of one brick = 1 sqm / 0.02 sqm = 50 bricks.
However, in Indian Standard (IS) codes and PWD practice for estimation, the 'standard' brick size often used for calculations is the non-modular size (approx. 230mm x 115mm x 75mm) or specific regional standards. For a half-brick wall (thickness of 115mm or 100mm), the standard analysis of cost for 1 sqm typically accounts for wastage and specific joint thicknesses.
According to standard PWD analysis of rates for a half-brick wall (using modular bricks with a slight allowance for wastage or specific jointing), the value is taken as 52.5 bricks per square meter.
- Option (a) 49.5 is slightly under the theoretical 50.
- Option (b) 52 is close but not the standard analysis figure.
- Option (c) 52.5 is the standard figure used in many PWD cost analysis tables to account for the modular size plus a small percentage of wastage.
- Option (d) 56.5 is too high for a standard half-brick wall.
Which of the following is deep foundation?
A)
Open foundation
B)
Mat foundation
C)
Pile foundation
D)
Isolated footing
Foundations are broadly classified into two categories based on their depth: Shallow Foundations and Deep Foundations.
1. Shallow Foundations: These are foundations where the depth (D) is generally less than or equal to the width (B) of the foundation. They transfer the load to the soil immediately below the base. Examples include:
- Open foundation (also known as spread footing)
- Isolated footing (a type of spread footing for a single column)
- Mat foundation (also known as raft foundation, used when soil bearing capacity is low or loads are heavy)
2. Deep Foundations: These are foundations where the depth is significantly greater than the width (D > B). They are used when the surface soil is too weak to support the structure, transferring the load to deeper, stronger strata or through skin friction.
- Pile foundation is the primary example of a deep foundation, consisting of long, slender columns driven or bored into the ground.
Therefore, among the given options, only the Pile foundation is classified as a deep foundation.
Based on structural behavior, pavements are generally classified into two categories.
A)
Bituminous & Concrete
B)
Flexible and rigid
C)
WBM & WMM
D)
All weather and fair weather
In Highway Engineering, pavements are classified based on their structural behavior (how they transmit loads to the subgrade) into two primary categories:
1. Flexible Pavements: These consist of a series of layers (sub-base, base, and surface) where the load is transferred grain-to-grain through the layers via shear. They have low flexural strength and deform under load (e.g., bituminous roads).
2. Rigid Pavements: These are typically made of Portland Cement Concrete (PCC). They possess high flexural strength (slab action), allowing them to distribute the wheel load over a wide area of the subgrade, resulting in minimal deformation (e.g., concrete roads).
Why other options are incorrect:
- Option (a) refers to the materials used, not the structural behavior.
- Option (c) WBM (Water Bound Macadam) and WMM (Wet Mix Macadam) are specific types of base/sub-base construction methods, not general structural classifications.
- Option (d) refers to the usability of the road based on weather conditions, not its structural engineering behavior.
While choosing ideal bridge site, which of the following below is not a desirable characteristic of the bridge site?
A)
Straight reach of the river
B)
A slow current portion having wide channel.
C)
Suitable high banks above HFL on each side
D)
Rock or other hard inerodible strata close to the river bed level.
When selecting an ideal site for a bridge, the goal is to minimize construction costs, ensure structural stability, and reduce the risk of scouring.
1. **Option (a) Straight reach of the river:** This is a desirable characteristic because it minimizes the length of the bridge and reduces the risk of river meandering or shifting the channel over time.
2. **Option (b) A slow current portion having wide channel:** This is NOT desirable. While a slow current is generally good, a **wide channel** increases the total length of the bridge, which significantly increases the cost of construction and the number of spans required. An ideal site is typically where the river is narrow (the shortest crossing distance) while maintaining a stable current.
3. **Option (c) Suitable high banks above HFL (High Flood Level):** This is desirable because it ensures that the bridge approaches are safe from flooding and prevents the banks from being washed away during peak flows.
4. **Option (d) Rock or other hard inerodible strata close to the river bed level:** This is highly desirable because it provides a strong foundation for piers and abutments, reducing the depth of excavation and preventing 'scouring' (the removal of soil around the foundation by flowing water).