Past Questions — 2026

In water supply systems, the primary requirement is to move large volumes of water (high discharge) at moderate pressures. Centrifugal pumps are the most commonly adopted because they are simple in design, easy to maintain, occupy less space, and provide a continuous, non-pulsating flow of water. Comparison with other options: - Reciprocating pumps (b): These are positive displacement pumps used for very high heads but low discharge. They produce pulsating flow and are mechanically complex, making them unsuitable for general water supply distribution. - Rotary pumps (c): These are typically used for high-viscosity fluids (like oils) rather than water. - Submersible pumps (d): While widely used for deep wells, a submersible pump is essentially a specialized version of a centrifugal pump (multistage) designed to operate underwater. The broader category of 'centrifugal pumps' encompasses the general technology used across the majority of water supply infrastructure (including surface water pumping stations).

Twin pit latrines are commonly adopted in rural sanitation because they are simple, low-cost, and suitable for areas without sewerage systems. They allow one pit to be used while the other rests and decomposes waste, making the system hygienic and practical for villages. Airports and hotels generally use flush toilets connected to sewerage or treatment systems, and industries typically require more advanced sanitation and waste management arrangements, so they are not the usual setting for twin pit latrines.

Step-by-step reasoning: 1. Analysis of the device: A Hand Pump Tube Well is a manual lifting mechanism used to extract groundwater from an aquifer through a bored well. 2. Capacity and Scale: Because it is manually operated, the discharge rate is relatively low compared to motorized pumps. This makes it unsuitable for large-scale applications like commercial irrigation, hydropower generation, or navigation. 3. Application: Hand pumps are ideal for small communities, individual households, and remote areas where electricity is unavailable or expensive. Therefore, they are the primary source of potable water in rural water supply schemes. 4. Evaluation of options: (a) Irrigation usually requires high-volume water flow provided by electric or diesel pumps. (b) Hydropower requires flowing surface water or high-head reservoirs. (c) Navigation requires large bodies of open water (rivers/canals). (d) Rural water supply matches the scale and function of a hand pump.

A four-bar chain (or four-bar linkage) is the simplest movable closed-chain mechanism. It consists of four rigid links connected by four kinematic pairs. Step-by-step breakdown: 1. Definition of a Kinematic Pair: A kinematic pair is a joint between two links that permits relative motion. 2. Structure of a Four-Bar Chain: It consists of one fixed link (frame), two crank/rocker links, and one coupler link. 3. Counting the Joints: - Joint 1: Between the fixed link and the first moving link. - Joint 2: Between the first moving link and the coupler link. - Joint 3: Between the coupler link and the second moving link. - Joint 4: Between the second moving link and the fixed link. Since there are 4 links connected in a closed loop, there are exactly 4 kinematic pairs (typically revolute joints). Verification using Grubler's Criterion for planar mechanisms: Degree of Freedom (F) = 3(n - 1) - 2j For a four-bar chain, F = 1, n = 4 links. 1 = 3(4 - 1) - 2j 1 = 9 - 2j 2j = 8 j = 4 pairs.

Planning a water supply scheme follows a logical engineering sequence. Before any physical construction or equipment selection can occur, the engineer must understand the existing conditions of the site. 1. **Survey and Investigation (Correct):** This is the foundational step. It involves assessing the population, forecasting future water demand, identifying potential water sources (surface or groundwater), analyzing the topography of the land, and studying the soil conditions. Without this data, it is impossible to design the system. 2. **Pump Selection (Incorrect):** Pump selection is a detailed design phase that happens only after the source is identified and the total dynamic head (TDH) and flow rate are calculated based on the survey data. 3. **Reservoir Construction (Incorrect):** Construction is one of the final implementation phases. The capacity and location of the reservoir are determined during the design phase, which follows the survey. 4. **Pipe Laying (Incorrect):** Pipe laying is part of the execution/construction phase. The diameter, material, and route of the pipes are decided based on the hydraulic calculations derived from the initial survey and investigation.

In a CI (Compression Ignition) engine, air is compressed to a very high pressure, which raises its temperature sufficiently to ignite the injected fuel spontaneously. Therefore, ignition occurs due to the high temperature of compressed air. The other options are incorrect: a spark plug is used in SI (spark ignition) engines, a glow plug is only an auxiliary starting aid in some diesel engines and is not the primary cause of ignition, and a carburettor is used to mix air and fuel in SI engines, not for ignition in CI engines.

The design of pumping mains (the pipelines used to transport fluid from a pump to its destination) focuses on hydraulic parameters to ensure the system operates efficiently and safely. 1. **Flow rate (b):** This is a primary design parameter. The diameter of the pipe is selected based on the required flow rate to maintain an optimal velocity, preventing both sedimentation (if too slow) and excessive friction losses or water hammer (if too fast). 2. **Head (d):** The total dynamic head (TDH), which includes static lift and friction losses, is critical for selecting the pump capacity and determining the pressure rating (class) of the pipes used in the main. 3. **Efficiency (c):** System efficiency (including pump efficiency and minimizing frictional head loss) is essential for calculating power requirements and operational costs. **Turbidity (a)** refers to the cloudiness or haziness of a fluid caused by individual particles. While turbidity is a critical parameter for water *treatment* and *quality* analysis, it does not influence the hydraulic design, pipe sizing, or pressure calculations of the pumping mains themselves.

Rainwater harvesting (RWH) is the process of collecting, filtering, and storing rainwater from surfaces (like rooftops or open grounds) for future use or for recharging groundwater aquifers. 1. Why Option (b) is correct: The primary objective of RWH is to reduce reliance on groundwater and municipal supplies, prevent the waste of rainwater, and ensure a sustainable water supply, thereby conserving water resources. 2. Why Option (a) is incorrect: RWH aims to provide a clean water source; it does not intend to increase the generation of wastewater. 3. Why Option (c) is incorrect: RWH actually aims to *decrease* surface runoff. By capturing rain where it falls, it prevents water from flowing away rapidly into drains, which also helps in reducing urban flooding and soil erosion. 4. Why Option (d) is incorrect: While storing water in closed tanks may reduce evaporation compared to open reservoirs, the primary 'aim' of the entire harvesting system is conservation and resource management, not specifically the reduction of the evaporation process itself.

Step-by-step reasoning: 1. **Understanding Deep Bore Wells**: Deep bore wells involve lifting water from significant depths (often exceeding 20-30 meters). 2. **The Suction Limit**: Standard surface-mounted pumps (like centrifugal pumps) rely on suction. Due to atmospheric pressure, the theoretical maximum suction lift is about 10.3 meters, and in practice, it is limited to 6-8 meters. Therefore, they cannot lift water from deep bore wells. 3. **Submersible Pump Mechanism**: A submersible pump is designed to be fully immersed in the water. Instead of 'pulling' water up via suction, it 'pushes' the water upward using a multi-stage centrifugal impeller. This eliminates the suction lift limitation, making it the most efficient and suitable choice for deep wells. 4. **Evaluating Other Options**: - **Centrifugal pump (a)**: Generally surface-mounted; limited by suction lift. - **Reciprocating pump (b)**: While they can handle higher heads, they are bulky, have high maintenance due to valves, and are not practical for installation inside narrow bore wells. - **Air lift pump (d)**: These use compressed air to lift water. While they can work in deep wells, they have very low efficiency and require a constant supply of high-pressure air, making them less suitable than submersible pumps for general engineering applications.

Cavitation is a phenomenon that occurs in centrifugal pumps when the local pressure of the liquid drops below its vapor pressure at the operating temperature. This causes the liquid to boil and form vapor bubbles (cavities). When these bubbles move to regions of higher pressure (like the impeller eye or vanes), they collapse violently, creating shockwaves that erode the metal surface. Step-by-step reasoning: 1. The pressure at the suction side of the pump must be maintained above the vapor pressure of the liquid to prevent boiling. 2. If the suction pressure becomes too low (due to high suction lift, clogged intake, or high fluid temperature), the pressure drops below the vapor pressure. 3. This leads to the formation of vapor bubbles, which is the definition of cavitation. Analysis of other options: - (a) High discharge: While high flow rates can increase friction losses in the suction line (which indirectly lowers pressure), high discharge itself is not the primary cause; the pressure drop is the cause. - (c) High motor speed: Increasing speed increases the Net Positive Suction Head Required (NPSHr), which can make a pump more prone to cavitation, but the physical cause is still the resulting low pressure relative to vapor pressure. - (d) Excess lubrication: Lubrication pertains to the bearings and seals, not the hydraulic fluid path, and has no effect on cavitation.

GI pipe stands for Galvanized Iron pipe. Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting and corrosion. This is achieved by immersing the iron pipe in a bath of molten zinc. Analysis of options: - Option (a) Galvanized Iron: Correct. This is the standard industry term for iron pipes coated with zinc. - Option (b) Ground Iron: Incorrect. This is not a standard term for piping materials. - Option (c) General Iron: Incorrect. While iron is a general material, 'General Iron' is not a specific technical classification for pipes. - Option (d) Grey Iron: Incorrect. Grey iron (or Cast Iron) is a type of iron based on carbon content, but 'GI' specifically refers to the galvanization process, not the internal metallurgy of the iron.

Storm water drains are specifically designed to collect and convey rainwater runoff from roofs, roads, and open surfaces during rainfall. They are not meant for wastewater transport. Sewage is carried by sanitary sewers, industrial effluent by separate industrial/wastewater systems, and sludge is a concentrated solid-liquid waste handled in treatment plants, not storm drains.

In the Theory of Machines, kinematic pairs are classified based on the type of contact between the two mating elements: 1. **Lower Pair**: A pair is called a lower pair when the two mating elements have surface contact. Examples include sliding pairs, turning pairs, and screw pairs. 2. **Higher Pair**: A pair is called a higher pair when the two mating elements have point or line contact. Analysis of the options: - **a. Cam and Follower**: The contact between the cam profile and the follower is typically a point or a line. Therefore, it is a **Higher Pair**. - **b. Shaft rotating in a bearing**: The shaft and the bearing surface maintain surface contact throughout the rotation (Turning Pair). Therefore, it is a **Lower Pair**. - **c. Gear teeth connection**: The contact between two mating gear teeth occurs along a line. Therefore, it is a **Higher Pair**. - **d. Belt and pulley**: The contact between the belt and the pulley is a line contact. Therefore, it is a **Higher Pair**. Thus, the only lower pair among the given options is the shaft rotating in a bearing.

Segregation of solid waste is the process of dividing waste into different categories (such as biodegradable, non-biodegradable, recyclable, and hazardous) at the point where it is generated (the source). This is a critical step in Integrated Solid Waste Management (ISWM) because it prevents contamination of recyclables and organic waste, making subsequent treatment and disposal processes more efficient. Why other options are incorrect: - Option (a) Burning waste: This is known as incineration, which is a method of waste disposal/volume reduction, not segregation. - Option (c) Dumping waste: This refers to landfilling or open dumping, which is the final disposal stage. - Option (d) Compacting waste: This is a mechanical process used to reduce the volume of waste for easier transport or storage, not a method of separation.

PVC stands for Poly Vinyl Chloride, a common thermoplastic polymer used in pipes, insulation, and fittings. Option d is correct because it matches the standard expansion of PVC. The other options are incorrect: (a) Poly Vinyl Cement is not a valid term, (b) Plastic Vinyl Cement is incorrect and not the standard abbreviation, and (c) Poly Variable Chloride is meaningless in this context.

A hydrostatic test is a pressure test used to verify the structural integrity and leak-tightness of a piping system. According to standard engineering practices and most international codes (such as ASME B31.3 for process piping), the standard test pressure for a hydrostatic test is typically 1.5 times the design pressure or the maximum allowable working pressure (MAWP). Step-by-step reasoning: 1. Working Pressure: This is the pressure at which the system is designed to operate normally. 2. Safety Margin: To ensure the system can handle surges and to identify potential weak points or leaks, it must be tested at a pressure higher than the working pressure. 3. Standard Factor: A factor of 1.5 is widely accepted as the industry standard to provide a sufficient safety margin without risking the permanent deformation or rupture of the pipe walls. Analysis of other options: - Option (a) 2.5 times: This is generally too high and could lead to plastic deformation or failure of the piping system. - Option (c) Equal to working pressure: This would only prove the system works under normal conditions; it would not provide a safety margin to ensure integrity against pressure spikes. - Option (d) 2.0 times: While some specific high-pressure codes might use higher factors, 1.5 is the general 'typical' standard for field hydrostatic tests.

In water supply planning, population forecasting methods are used to estimate future water demand. 1. **Arithmetic Increase Method (Correct):** This method assumes that the population increases by a constant amount (a uniform growth rate in absolute terms) each decade. The formula is Pn = P0 + n*d, where 'd' is the average increase per decade. It is typically used for old, established cities where growth has stabilized. 2. **Geometric Increase Method:** This method assumes that the percentage growth rate remains constant, meaning the population grows exponentially. It is suitable for rapidly growing young cities. 3. **Incremental Increase Method:** This is a combination of the arithmetic and geometric methods. It accounts for the average increase as well as the incremental increase in that growth rate. 4. **Logistic Curve Method:** This method assumes that the population growth follows an S-shaped curve, starting slowly, accelerating, and then leveling off as it reaches a saturation limit (carrying capacity).

In the context of piping materials and civil/mechanical engineering, 'CI' is the standard abbreviation for Cast Iron. Cast iron pipes are widely used in water distribution and sewage systems due to their high compressive strength and durability. - Option (a) 'Cement Iron' is incorrect; while cement-lined cast iron pipes exist, the material itself is not called 'Cement Iron'. - Option (b) 'Circular Iron' is incorrect; while pipes are circular, this is not a material classification. - Option (d) 'Common Iron' is incorrect; this is not a technical term used in engineering material specifications.

In civil engineering estimation and costing, items are measured based on their dimensions. 1. Earthwork excavation (Option a): This involves removing a volume of soil (Length × Width × Depth), therefore it is measured in cubic metres (m³). 2. Brick masonry (Option b): While brick masonry is typically measured in cubic metres (m³), in many standardized competitive exams for Junior Engineers, if 'Earthwork' is listed, it is the primary example of volume-based measurement. However, technically, both (a) and (b) are measured in m³. In the context of standard multiple-choice questions for this specific syllabus, Earthwork is the most fundamental volume item. (Note: If the masonry is a thin partition wall, it is measured in square metres, but general masonry is m³). 3. Plastering (Option c): This is a surface treatment with a constant thickness, measured in square metres (m²). 4. Painting (Option d): This is a surface finish, measured in square metres (m²). Comparing the options, Earthwork excavation is universally measured in cubic metres regardless of the scale, making it the most definitive answer.

The Octane Number is a standard measure of the performance of a fuel (specifically gasoline/petrol) in resisting 'knocking' or 'pinging' during combustion in a spark-ignition (SI) engine. Knocking occurs when the fuel-air mixture detonates prematurely rather than burning smoothly. A higher octane number indicates a greater resistance to auto-ignition, allowing for higher compression ratios and improved engine efficiency. Analysis of other options: - Option (a) is incorrect because the ignition quality of diesel is measured by the 'Cetane Number', not the Octane Number. - Option (b) is incorrect because density is a physical property of the fuel and is not what the octane number measures. - Option (c) is incorrect because the calorific value refers to the amount of heat released during combustion per unit mass, which is independent of the octane rating.

To understand this question, we must define NPSH (Net Positive Suction Head). 1. NPSHA (Available NPSH) is the actual pressure available at the suction port of the pump, determined by the system installation (static head, friction losses, and vapor pressure). 2. NPSHR (Required NPSH) is the minimum pressure required at the suction port to prevent the liquid from boiling (flashing) and forming vapor bubbles, as specified by the pump manufacturer. Condition for Operation: For a pump to operate correctly without cavitation, NPSHA must be greater than NPSHR (NPSHA > NPSHR). When NPSHR is greater than NPSHA (NPSHR > NPSHA), the pressure at the impeller eye drops below the vapor pressure of the liquid. This causes 'cavitation'—the formation and sudden collapse of vapor bubbles. Severe cavitation leads to a drastic drop in discharge pressure, loss of prime, extreme vibration, and potential mechanical failure. In practical terms, if the cavitation is severe enough, the pump will fail to move fluid (it will 'not run' effectively or will be forced to shut down to prevent damage). Analysis of other options: - Option (a): This is the ideal condition for a pump to run smoothly. - Option (c): Water entering the suction pipe is a requirement for the pump to operate (priming). - Option (d): Good voltage is a prerequisite for the motor to drive the pump.

The loss of head due to friction in a pipe (pumping main) is calculated using the Darcy-Weisbach equation: h_f = (f * L * v^2) / (2 * g * D), where: 1. 'L' is the pipe length: Head loss is directly proportional to the length of the pipe. As the length increases, the friction surface increases, leading to higher head loss. 2. 'v' is the velocity of flow: Head loss is proportional to the square of the velocity. Higher flow speeds result in significantly higher frictional resistance. 3. 'D' is the pipe diameter: Head loss is inversely proportional to the diameter. A smaller diameter increases the velocity for a given flow rate and increases the relative effect of wall friction. Since the head loss depends on the length, the velocity, and the diameter of the pipe, all the provided options are correct.

The specific speed (Ns) of a pump is a dimensionless (or characteristic) index used to classify pumps based on their geometry and performance characteristics. It is defined as the speed of a geometrically similar pump that would deliver a unit discharge (Q = 1 m³/s or gpm) against a unit head (H = 1 m or ft). The standard formula for the specific speed of a centrifugal pump is: Ns = (N × √Q) / (H^(3/4)) Looking at the options provided: - Option (a) is mathematically incorrect and does not follow the laws of pump similarity. - Option (b) is incorrect as it lacks the required exponents for Q and H. - Option (c) represents the formula NS = (N Q / H^3/4). While the square root on Q is missing in the text of the option provided in the prompt, in the context of standard multiple-choice questions for this subject, this option is intended to represent the Ns ∝ N Q^0.5 / H^0.75 relationship. Among the given choices, (c) is the only one that correctly identifies the H^(3/4) relationship, which is the defining characteristic of pump specific speed. - Option (d) uses H^1/3, which is incorrect for centrifugal pumps.

The question asks for the primary purpose of the 'Mizoram Water Supply (Control) Act'. By analyzing the title of the Act itself, the keyword 'Water Supply' explicitly indicates the subject matter. In the context of Public Health Engineering Department (PHED) legislation, such Acts are designed to regulate the sourcing, treatment, distribution, and management of potable water to ensure public health and safety. - Option (a) Road construction is regulated by the Public Works Department (PWD). - Option (b) Forest management is regulated by the Forest Department. - Option (c) Electricity supply is regulated by the Power Department/Electricity Board. - Option (d) Water supply and distribution directly aligns with the title and mandate of the Act.

Step-by-step reasoning: 1. Definition of Power: In physics and engineering, power is defined as the rate at which work is done or energy is transferred over time. The formula is Power = Work / Time. 2. SI Unit of Power: The standard SI unit for power is the Watt (W), where 1 Watt = 1 Joule per second (J/s). In industrial and mechanical applications, such as pump power, the kilowatt (kW) is commonly used (1 kW = 1000 W). 3. Analysis of Options: - Option (a) kW (kilowatt): This is a unit of power. Correct. - Option (b) m³/s (cubic meters per second): This is the SI unit for volumetric flow rate (discharge), not power. - Option (c) N/m² (Newtons per square meter): This is the SI unit for pressure (also known as the Pascal, Pa), not power. - Option (d) rpm (revolutions per minute): This is a unit of rotational speed (angular velocity), not power. Therefore, the correct unit for pump power in the SI system is the kilowatt (kW).