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Past Questions — 2025
What happens to the conductivity of a semiconductor when temperature increases?
A)
It decreases
B)
It remains constant
C)
It increases
D)
It becomes zero
In a semiconductor, the valence band is full and the conduction band is empty at absolute zero (0K). As the temperature increases, thermal energy is provided to the electrons in the valence band. This energy allows more electrons to overcome the energy band gap (Eg) and jump from the valence band to the conduction band. This process creates free electrons in the conduction band and holes in the valence band, both of which act as charge carriers. Since conductivity (σ) is proportional to the concentration of charge carriers (n), an increase in temperature leads to an increase in the number of available carriers, thereby increasing the conductivity of the semiconductor. This is the opposite behavior of metals (conductors), where conductivity decreases as temperature increases due to increased lattice vibrations (scattering).
The slope of an open channel affects:
A)
Width of pipe
B)
Flow velocity
C)
Temperature
D)
Odour level
In open channel hydraulics, the flow is primarily driven by gravity. The slope of the channel (bed slope) provides the gravitational force that overcomes the frictional resistance of the channel walls and bed. According to Manning's Equation (V = (1/n) * R^(2/3) * S^(1/2}), where V is the average velocity, n is the Manning's roughness coefficient, R is the hydraulic radius, and S is the slope of the energy grade line (which is approximately the bed slope for uniform flow), the velocity (V) is directly proportional to the square root of the slope (S). Therefore, increasing the slope increases the flow velocity.
Why other options are incorrect:
- a. Width of pipe: The width is a geometric design parameter determined by the required discharge capacity, not by the slope itself.
- c. Temperature: Temperature is a thermodynamic property of the fluid and is not affected by the physical slope of the channel.
- d. Odour level: Odour is related to the chemical composition and biological activity (e.g., anaerobic conditions) of the water, not the slope of the channel.
What is the main purpose of using a starter for motors in a pumping station?
A)
To reduce water flow
B)
To cool the motor
C)
To limit starting current
D)
To increase voltage
When an electric motor (especially an induction motor used in pumping stations) is started directly from the mains, it draws a very high initial current, often 5 to 7 times its rated full-load current. This is because the motor starts from a standstill (zero speed), meaning there is no back-EMF to oppose the supply voltage. This high 'inrush current' can cause voltage dips in the power system, damage the motor windings due to overheating, and put excessive mechanical stress on the pump couplings. A motor starter (such as a Star-Delta starter or an Auto-transformer starter) is used to reduce the starting voltage applied to the motor, thereby limiting the starting current to a safe level.
Analysis of other options:
- (a) To reduce water flow: Water flow is controlled by valves or Variable Frequency Drives (VFDs), not by the starter.
- (b) To cool the motor: Cooling is handled by fans or cooling jackets; starters do not provide cooling.
- (d) To increase voltage: Starters are designed to either maintain or temporarily reduce voltage to protect the motor; they are not used to increase voltage.
What is the primary purpose of rainwater harvesting?
A)
Increase humidity
B)
Recharge groundwater and reduce water shortage
C)
Prevent soil erosion
D)
Cool the environment
Rainwater harvesting (RWH) is the technique of collecting and storing rainwater for reuse or directing it into the ground to replenish aquifers.
1. Why Option (b) is correct: The primary engineering and environmental goals of RWH are to mitigate water scarcity (by providing an alternative water source) and to raise the water table (groundwater recharge), which is critical for sustainable water management in Public Health Engineering.
2. Why other options are incorrect:
- Option (a): Increasing humidity is not a goal of water harvesting; in fact, excessive humidity can be undesirable in many climates.
- Option (c): While RWH can indirectly help by reducing surface runoff, the primary method for preventing soil erosion is through vegetation, terracing, or check dams, not harvesting for storage/recharge.
- Option (d): While urban greenery (supported by harvested water) can cool an environment, the 'primary purpose' of the harvesting system itself is water security, not temperature control.
A septic tank system is mainly used in:
A)
Rural and semi-urban areas
B)
Industrial treatment plants
C)
Desalination
D)
Water distribution
A septic tank is a small-scale, decentralized wastewater treatment system. It is primarily used in locations where a centralized municipal sewerage system (public sewers) is unavailable or impractical to install.
1. Why Option (a) is correct: In rural and semi-urban areas, houses are often spread apart, making the cost of laying extensive sewer lines prohibitively expensive. A septic tank provides an on-site solution for the primary treatment of domestic sewage through anaerobic digestion and sedimentation.
2. Why Option (b) is incorrect: Industrial treatment plants handle high volumes of complex chemical waste and require large-scale, specialized treatment processes (like activated sludge or chemical precipitation) that a simple septic tank cannot manage.
3. Why Option (c) is incorrect: Desalination is the process of removing salts from seawater to produce fresh water; it is a water production process, not a wastewater treatment process.
4. Why Option (d) is incorrect: Water distribution refers to the system of pipes and pumps used to deliver potable water to consumers, which is the opposite end of the water cycle from sewage treatment.
Curing should be done for at least:
A)
3 days
B)
5 days
C)
7 days
D)
28 days
Curing is the process of maintaining satisfactory moisture content and temperature in concrete to allow the hydration of cement to proceed, ensuring the concrete reaches its intended strength and durability. According to standard engineering practices and codes (such as IS 456 for Indian contexts, which is typically followed in government departmental exams in India), the minimum period for curing concrete is generally 7 days for Ordinary Portland Cement (OPC) under normal conditions. While curing for 14 or 28 days is ideal for maximum strength gain, the 'at least' threshold for standard structural concrete is 7 days. Options (a) 3 days and (b) 5 days are insufficient for proper hydration, and (d) 28 days is the period for full strength gain/testing, not the minimum required curing duration.
A combined drainage system carries:
A)
Only sewage
B)
Only storm water
C)
Both sewage and storm water
D)
Treated effluent
In sanitary engineering, drainage systems are categorized based on the type of wastewater they transport.
1. **Separate System**: This system uses two distinct sets of pipes—one for sanitary sewage (domestic and industrial waste) and another for storm water (rainwater runoff).
2. **Combined System**: This system uses a single set of sewers to carry both sanitary sewage and storm water together to the treatment plant or disposal point.
3. **Partially Separate System**: A hybrid where some storm water (e.g., from roofs) enters the sanitary sewer, while the rest is handled separately.
Therefore, a 'combined drainage system' specifically refers to the infrastructure that carries both sewage and storm water.
- Option (a) describes a separate sanitary sewer.
- Option (b) describes a separate storm sewer.
- Option (d) refers to the output of a treatment plant, not the collection system.
Coagulation in water treatment helps in:
A)
Removing color
B)
Killing bacteria
C)
Settling suspended particles
D)
Reducing hardness
Coagulation is a chemical process used in water treatment to destabilize colloidal particles. Most suspended particles in raw water are negatively charged, which causes them to repel each other and remain in suspension (preventing them from settling). By adding a coagulant (like Alum or Ferric Chloride), positive ions neutralize these negative charges, allowing the particles to collide and form larger aggregates called 'flocs'. These larger flocs have a higher settling velocity and can be easily removed by sedimentation (settling) and subsequent filtration.
Why other options are incorrect:
- Option (a): While coagulation can help remove some organic color, its primary and fundamental purpose is the removal of turbidity/suspended solids. Color removal is often a secondary benefit or requires specific advanced oxidation/adsorption processes.
- Option (b): Killing bacteria is the purpose of 'Disinfection' (e.g., chlorination, UV radiation), not coagulation.
- Option (d): Reducing hardness is achieved through 'Water Softening' processes (e.g., ion exchange, lime-soda process), not coagulation.
For water-retaining structures, the maximum water-cement ratio is:
A)
0.65
B)
0.55
C)
0.50
D)
0.45
In concrete technology, water-retaining structures (such as water tanks, reservoirs, and dams) require high impermeability to prevent leakage and protect the reinforcement from corrosion. The permeability of concrete is directly proportional to the water-cement (w/c) ratio; a lower w/c ratio results in a denser cement paste with fewer interconnected capillary pores. According to standard engineering codes (such as IS 456 and IS 3370 for water-retaining structures), the water-cement ratio for such structures is strictly limited to ensure durability and water-tightness. While general reinforced concrete may allow higher ratios, water-retaining structures typically mandate a maximum w/c ratio of 0.45 to 0.50. In the context of competitive exams for Junior Engineers, 0.45 is the recognized standard maximum limit to ensure the required low permeability. Options a (0.65), b (0.55), and c (0.50) are too high and would result in porous concrete, leading to seepage and reduced service life.
Night soil collection refers to:
A)
Manual collection of human waste
B)
Storage of rainwater
C)
Collection of grey water
D)
Water sample testing
In the context of sanitation and environmental engineering, 'night soil' is a traditional term used to describe human excreta (feces and urine) that is collected from pit latrines or buckets rather than being carried away by a sewerage system. 'Night soil collection' specifically refers to the practice of removing this waste manually or via vacuum trucks, typically during the night to minimize public nuisance and odor.
Analysis of other options:
- Option b (Storage of rainwater) refers to rainwater harvesting.
- Option c (Collection of grey water) refers to the management of wastewater from baths, sinks, and washing machines (excluding toilets).
- Option d (Water sample testing) refers to water quality analysis.
HDPE pipes are mostly preferred for:
A)
Electrical wiring
B)
Portable water supply due to flexibility
C)
Sewer lines only
D)
Road construction
Step-by-step reasoning: 1. HDPE (High-Density Polyethylene) is a thermoplastic polymer known for its high strength-to-density ratio, chemical resistance, and significant flexibility. 2. In the context of Water Supply Engineering (the subject of the exam), HDPE is widely preferred for potable (drinking) water distribution because it is non-toxic, corrosion-resistant, and its flexibility allows it to accommodate ground movement and be installed in undulating terrains without requiring numerous joints. 3. Analysis of other options: (a) While HDPE can be used as conduits for electrical wiring, it is not the 'most preferred' use in the context of a Civil Engineering/Water Supply exam. (c) While used in some sewer applications, it is not used 'only' for sewer lines; its primary advantage in PHED (Public Health Engineering Department) contexts is water distribution. (d) HDPE is not a primary material for road construction itself, though it may be used for drainage pipes beneath roads. Note: The word 'Portable' in the option is a common typographical error in technical exams for 'Potable' (meaning drinkable).
The process of separating biodegradable and non-biodegradable waste is called:
A)
Disposal
B)
Segregation
C)
Collection
D)
Treatment
Step-by-step reasoning:
1. Analysis of the process: The question asks for the term used when waste is divided into different categories (specifically biodegradable and non-biodegradable).
2. Evaluating Option (b) Segregation: In Solid Waste Management, 'segregation' is the formal process of dividing waste into different groups (e.g., wet waste/biodegradable, dry waste/non-biodegradable, and hazardous waste) at the source or at a processing plant. This is the correct technical term.
3. Evaluating Option (a) Disposal: Disposal refers to the final placement of waste in a landfill or incineration plant after all other processes are complete.
4. Evaluating Option (c) Collection: Collection is the act of gathering waste from various points (households, commercial areas) and transporting it to a transfer station or disposal site.
5. Evaluating Option (d) Treatment: Treatment refers to the physical, chemical, or biological processes used to change the characteristics of waste (e.g., composting or anaerobic digestion) to make it less harmful or to recover resources.
Conclusion: Since the action described is the separation of waste types, 'Segregation' is the only correct answer.
Which of the following is not a type of masonry work?
A)
Brick
B)
Stone
C)
RCC
D)
Laterite
Masonry is defined as the building of structures from individual units (usually rectangular blocks) laid in and bound together by mortar.
1. Brick Masonry (Option a): This is a classic type of masonry where bricks are laid in courses with mortar.
2. Stone Masonry (Option b): This involves using natural stones (rubble or ashlar) bound by mortar, which is a fundamental type of masonry.
3. Laterite Masonry (Option d): Laterite is a soil type rich in iron and aluminum that hardens upon exposure to air; it is commonly used as blocks in masonry work in tropical regions.
4. RCC (Reinforced Cement Concrete) (Option c): RCC is a composite material consisting of concrete (a mixture of cement, aggregates, and water) reinforced with steel bars. It is a cast-in-place or pre-cast monolithic structural material, not a masonry work, as it does not consist of individual units laid with mortar.
The standard duration for water tightness test is:
A)
6 hours
B)
12 hours
C)
24 to 72 hours
D)
7 days
A water tightness test (also known as a hydrostatic test) is conducted on water tanks to ensure there are no leakages through the walls, floor, or joints before the tank is put into service. According to standard engineering practices and various building codes (such as IS codes or BS standards), the tank is filled with water and monitored for a specific period. The standard duration for this test is typically between 24 to 72 hours. During this time, the drop in water level is measured; a negligible drop (accounting for evaporation) indicates that the tank is watertight. Options a and b (6 and 12 hours) are too short to detect slow seepage or structural leaks, while option d (7 days) is generally excessive for standard departmental testing requirements unless specified for specialized high-pressure vessels.
What is the major advantage of ERW pipes?
A)
High flexibility
B)
Corrosion resistance
C)
Smooth surface and economical
D)
Fire resistance
ERW stands for Electric Resistance Welding. These pipes are manufactured from steel strips or sheets that are cold-formed into a cylindrical shape and then welded longitudinally using high-frequency electric current.
1. Why 'Smooth surface and economical' is correct: Because ERW pipes are produced from rolled steel sheets, they have a very smooth internal surface, which reduces frictional losses (head loss) in water supply systems. Furthermore, the mass-production process of ERW is significantly more cost-effective (economical) than seamless pipes or cast iron pipes.
2. Why other options are incorrect:
- (a) High flexibility: Steel pipes are rigid; they do not possess 'high flexibility' compared to HDPE or PVC pipes.
- (b) Corrosion resistance: Steel is highly susceptible to corrosion unless coated or galvanized. Therefore, corrosion resistance is a disadvantage, not a major advantage.
- (d) Fire resistance: While steel is non-combustible, 'fire resistance' is not the primary 'major advantage' considered when selecting pipes for water supply infrastructure compared to hydraulic efficiency and cost.
Which of the following materials is commonly used in hand pump tube wells?
A)
PVC
B)
GI
C)
RCC
D)
Copper
In the construction of hand pump tube wells, the casing pipe and the riser pipe must be able to withstand significant mechanical stress, including the weight of the pump assembly, the tension from the pump handle operation, and the external pressure from the surrounding soil.
1. **GI (Galvanized Iron)**: This is the most common material used for hand pump tube wells because it provides high structural strength, durability, and resistance to corrosion (due to the zinc coating). It can handle the mechanical stresses of the pumping mechanism without collapsing or breaking.
2. **PVC (Polyvinyl Chloride)**: While used in some modern shallow wells or as liners, standard PVC lacks the structural rigidity and tensile strength required for the riser pipes of traditional hand pumps, where the pump cylinder is suspended.
3. **RCC (Reinforced Cement Concrete)**: RCC is used for the well rings of 'open wells' or 'dug wells,' but it is physically impossible to use it as a 'tube' in a tube well, which requires a narrow diameter drilled into the ground.
4. **Copper**: Copper is far too expensive and lacks the necessary structural strength for this application; it is typically used for internal plumbing or electrical wiring, not for well casings.
Turbidity in water is measured in:
A)
mg/L
B)
ppm
C)
NTU
D)
pH units
Turbidity is a measure of the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye.
1. **NTU (Nephelometric Turbidity Units):** This is the standard unit used to measure turbidity. It is based on the principle of nephelometry, which measures the intensity of light scattered at a 90-degree angle to the incident light beam. The more particles present in the water, the more light is scattered, resulting in a higher NTU value.
2. **Why other options are incorrect:**
- **mg/L (milligrams per liter):** This is a unit of concentration used for Total Suspended Solids (TSS) or dissolved chemicals, not for the optical property of turbidity.
- **ppm (parts per million):** This is another unit of concentration (equivalent to mg/L in water) used for chemical impurities or pollutants.
- **pH units:** This is a logarithmic scale used to specify the acidity or basicity of an aqueous solution, unrelated to the clarity of the water.
The main purpose of a soak pit in rural sanitation is to:
A)
Allow percolation of wastewater
B)
Store drinking water
C)
Trap solid waste
D)
Collect rainwater
A soak pit (also known as a seepage pit) is a covered, porous-walled chamber that allows effluent (wastewater) to slowly soak into the ground. In rural sanitation, it is typically used as the final disposal point for wastewater coming from a septic tank. The primary mechanism is 'percolation,' where the liquid wastewater filters through the soil, which acts as a natural biological filter.
Why other options are incorrect:
- Option b: Drinking water is stored in tanks or reservoirs, not soak pits, as soak pits are designed for waste disposal.
- Option c: Solid waste is trapped in the septic tank (as sludge) or a grease trap, not the soak pit. If solids enter a soak pit, they can clog the soil pores and cause the pit to fail.
- Option d: Rainwater is collected in rainwater harvesting pits or tanks; while a soak pit can handle some runoff, its primary engineering purpose in a sanitation system is the disposal of greywater or septic effluent.
Which among the following is not a method of population forecasting in civil engineering?
A)
Arithmetical increase
B)
Geometric increase
C)
Logistic curve
D)
Standard Proctor
In Water Supply Planning, population forecasting is essential to design the capacity of water treatment plants and distribution networks. The common methods used are:
1. Arithmetical Increase Method: Assumes a constant rate of growth per decade. It is typically used for old, established cities.
2. Geometric Increase Method: Assumes a constant percentage growth rate. It is generally used for rapidly growing young cities.
3. Logistic Curve Method: Assumes that the population growth follows a sigmoid curve, reaching a saturation limit (carrying capacity). It is used for cities that have already passed their peak growth phase.
Option (d), the 'Standard Proctor' test, is a laboratory method used in Soil Mechanics and Geotechnical Engineering to determine the optimal moisture content and maximum dry density of a soil sample for compaction. It has no relation to population forecasting in civil engineering.
The key reason for conducting a water supply survey is to:
A)
Increase groundwater level
B)
Assess rainfall patterns
C)
Improve road network
D)
Plan intake and reservoir location
A water supply survey is a comprehensive preliminary investigation conducted to gather all necessary data required to design a sustainable and efficient water supply system for a community. The primary objectives of such a survey include: 1. Determining the current and future water demand (population projection). 2. Identifying available water sources (surface or groundwater). 3. Analyzing the topography of the land to determine the most economical locations for the intake structures (where water is collected) and reservoirs/service reservoirs (where water is stored and distributed via gravity or pumping).
Why other options are incorrect:
- Option (a): Increasing groundwater level is a result of rainwater harvesting or groundwater recharge projects, not a survey goal.
- Option (b): Assessing rainfall patterns is a part of hydrological data collection, but it is a subset of the survey, not the 'key reason' for the overall water supply planning.
- Option (c): Improving the road network is the objective of transportation or civil infrastructure engineering, not water supply engineering.
In water supply engineering, excess iron in drinking water can cause:
A)
Hardness
B)
Taste and staining issues
C)
Increased pH
D)
Foam formation
Step-by-step reasoning:
1. Analysis of Iron in Water: Iron is commonly found in groundwater. While it is not typically toxic in the concentrations found in drinking water, it is considered an 'aesthetic' contaminant.
2. Effects of Iron: When iron is oxidized (exposed to air), it forms ferric hydroxide precipitates. These precipitates cause a distinct metallic taste and leave reddish-brown or orange stains on laundry, sanitary fixtures (sinks, tubs), and plumbing.
3. Evaluating Options:
- (a) Hardness: Hardness is primarily caused by multivalent metallic cations, specifically Calcium (Ca2+) and Magnesium (Mg2+). Iron does not significantly contribute to the standard measure of water hardness.
- (b) Taste and staining issues: This is the primary characteristic of excess iron in water supply.
- (c) Increased pH: Iron concentration does not inherently increase the pH of water; pH is a measure of hydrogen ion concentration.
- (d) Foam formation: Foaming is typically associated with the presence of surfactants (detergents) or high organic matter, not dissolved iron.
The term “characterization” in solid waste management refers to:
A)
Identifying components and types of waste
B)
Incinerating solid waste
C)
Burying waste
D)
Burning waste
In Solid Waste Management (SWM), 'characterization' is the process of determining the physical and chemical composition of the waste stream. This involves identifying the different components (such as organic matter, plastics, paper, glass, and metals) and the types of waste (hazardous, non-hazardous, recyclable, etc.) present in a sample. This step is critical for designing appropriate collection, transport, and disposal systems, as well as for determining the feasibility of recycling or composting.
Why other options are incorrect:
- Option b (Incinerating solid waste) refers to thermal treatment or combustion, which is a method of disposal/volume reduction, not characterization.
- Option c (Burying waste) refers to landfilling, which is a final disposal method.
- Option d (Burning waste) is a general term for incineration or open burning, which is a disposal process.
The minimum thickness of an RCC base slab in a water tank should generally be:
A)
100 mm
B)
150 mm
C)
200 mm
D)
250 mm
In the design of Reinforced Cement Concrete (RCC) water tanks, the thickness of the base slab is governed by two primary factors: structural strength (to resist the weight of the water and the slab itself) and water-tightness (to prevent seepage). According to standard engineering practices and various codes of practice for liquid retaining structures (such as IS 3370), a minimum thickness is prescribed to ensure adequate concrete cover for the reinforcement to prevent corrosion and to ensure the slab remains impermeable. For most standard water tanks, the minimum thickness of the RCC base slab is generally taken as 150 mm. This thickness provides sufficient space for two layers of reinforcement (top and bottom) while maintaining the required clear cover (usually 40-50 mm) to protect the steel from moisture and chemicals in the soil. Options a (100 mm) is typically too thin for a base slab to ensure durability and water-tightness, while options c (200 mm) and d (250 mm) may be required for larger tanks based on structural calculations, but they are not the general 'minimum' requirement.
The pipe appurtenance that releases trapped air in pipelines is:
A)
Check valve
B)
Non-return valve
C)
Sluice valve
D)
Air valve
In water supply engineering, pipe appurtenances are devices fitted to pipelines to control flow, maintain pressure, and ensure the efficiency of the system.
1. **Air Valve (Correct):** Air valves are specifically designed to release trapped air that accumulates at high points of a pipeline. Trapped air can cause 'air locks,' which restrict water flow and increase head loss, or cause water hammer effects. Air release valves allow air to escape while preventing water from leaking out.
2. **Check Valve / Non-return Valve (Incorrect):** Options (a) and (b) refer to the same type of device. A check valve (or non-return valve) allows water to flow in only one direction and prevents backflow, protecting pumps and equipment from reverse flow.
3. **Sluice Valve (Incorrect):** A sluice valve (also known as a gate valve) is used to completely stop or start the flow of water in a pipe, typically for maintenance or isolation purposes. It is not used for air removal.
Which brick is considered the best quality?
A)
Second-class brick
B)
Overburnt brick
C)
First-class brick
D)
Sun-dried brick
Bricks are classified based on their quality, strength, and appearance.
1. **First-class bricks (Option c):** These are the highest quality bricks. They are thoroughly burnt, have a uniform deep red or copper color, possess sharp and square edges, and produce a clear metallic ringing sound when struck together. They have the lowest water absorption and the highest compressive strength, making them ideal for permanent structures and load-bearing walls.
2. **Second-class bricks (Option a):** These are slightly inferior to first-class bricks. They may have slight irregularities in shape or color and have a slightly higher water absorption rate. They are used for internal walls or where plastering is intended.
3. **Overburnt bricks (Option b):** These bricks are burnt beyond the required temperature, resulting in a dark purple or blackish color and a distorted shape. While they are very hard and durable, they are not considered 'best quality' for general masonry due to their irregularity and brittleness.
4. **Sun-dried bricks (Option d):** These are not burnt in a kiln but dried in the sun. They have very low strength and high water absorption, making them unsuitable for permanent engineering structures; they are typically used only for temporary works.