Past Questions

The air filter is a critical component of the engine intake system. Its primary function is to act as a barrier that traps airborne contaminants—such as dust, dirt, pollen, and other debris—before the air enters the combustion chamber. If these particles were allowed to enter the engine, they would act as abrasives, causing premature wear and tear on the cylinder walls, piston rings, and valves, eventually leading to engine failure. Analysis of other options: - Option (a): While a clean air filter helps maintain optimal performance, the 'primary purpose' is protection, not performance enhancement itself. - Option (c): Cooling the engine is the primary purpose of the radiator and cooling system, not the air filter. - Option (d): The air filter is typically located inside the engine bay or a housing and is not a cosmetic feature designed to make the car look nicer.

Arc welding is a fusion welding process that uses an electric arc to create heat to melt and join metals. An electric arc is formed between an electrode and the base material; the high current flowing through this ionized gas gap generates intense heat (typically between 3,000°C to 20,000°C), which melts the metals to form a weld pool. Why other options are incorrect: - a. Friction: This is the heat source for Friction Welding, where mechanical rubbing generates heat. - b. Resistance Heating: This is the heat source for Resistance Welding (e.g., Spot Welding), where heat is generated by the electrical resistance of the materials to the current flow. - c. Chemical Reaction: This is the heat source for Thermite Welding, where an exothermic chemical reaction between aluminum powder and metal oxide is used.

A bevel protractor is a precision measuring instrument specifically designed to measure angles with high accuracy. It typically consists of a base (stock) and a rotating blade (bevel) connected by a pivot, often equipped with a vernier scale to measure angles down to a few minutes of a degree. Analysis of other options: - Internal Diameter: Measured using internal calipers, inside micrometers, or bore gauges. - Straightness: Verified using a straight edge, spirit level, or an autocollimator. - Thread pitch: Measured using a screw pitch gauge or a micrometer.

Step-by-step reasoning: 1. **Function of a Pressure Relief Valve (PRV):** In a lubrication system, the oil pump delivers oil at a rate that may exceed the system's requirements or the capacity of the bearings/galleries to absorb it, especially at high engine speeds. A pressure relief valve is a safety mechanism designed to open when the system pressure reaches a predetermined maximum limit. 2. **Mechanism:** When the pressure exceeds the spring tension of the valve, the valve opens and diverts the excess oil back to the oil sump or the pump inlet, thereby capping the maximum pressure. 3. **Why Option 'b' is correct:** Its primary purpose is to protect the system components (such as oil filters, seals, and gaskets) from bursting or leaking due to excessive pressure. 4. **Why other options are incorrect:** - Option 'a' (Regulate flow): While it affects flow, 'regulation' usually implies maintaining a specific flow rate for operation, whereas a relief valve is specifically for over-pressure protection. - Option 'c' (Cool the oil): Oil cooling is handled by an oil cooler (heat exchanger) or the oil sump. - Option 'd' (Filter the oil): Oil filtration is performed by the oil filter or strainer.

Step-by-step reasoning: 1. The keyword in the question is 'suddenly fails'. This implies an instantaneous break in the electrical circuit. 2. A blown fuse (Option a) is designed to break the circuit immediately if there is an overcurrent or short circuit, leading to a sudden loss of power to the specific component (the headlights). 3. A dead battery (Option b) or a faulty alternator (Option c) would typically cause a gradual dimming of lights or a total failure of all electrical systems (including the engine starting system), rather than just the headlights suddenly failing while the car is likely operational. 4. While a loose ground connection (Option d) can cause failure, it often manifests as flickering or intermittent failure before a total break, whereas a fuse 'blows' instantly. Therefore, in the context of a sudden failure of a specific circuit, a blown fuse is the most likely and common cause.

Step-by-step reasoning: 1. Definition of Arc Welding: Arc welding is a process that uses an electric arc to create intense heat to melt the base metals and usually a filler material to join two pieces of metal together. 2. Classification of Welding: Welding processes are broadly categorized based on whether the base metal is melted or not. - Fusion Welding: Processes where the base metal is melted to form a pool of molten metal that solidifies to create a joint. Examples include Arc welding, Gas welding, and Laser beam welding. - Solid-state Welding: Processes where joining occurs without melting the base metal, typically using pressure and heat below the melting point. Examples include Friction welding and Forge welding. 3. Evaluating Options: - Option (a) Solid-state Welding: Incorrect, as arc welding involves melting the metal. - Option (b) Fusion Welding: Correct, as the electric arc melts the metal to create a fusion joint. - Option (c) Resistance Welding: While resistance welding uses electricity, it is a specific sub-category that relies on electrical resistance and pressure; arc welding relies on an open electric arc. - Option (d) Pressure Welding: Incorrect, as arc welding relies on heat/melting rather than primary mechanical pressure to achieve the bond.

In a two-stroke internal combustion engine, the functions of intake, compression, power, and exhaust are completed in just two strokes of the piston. Unlike a four-stroke engine, which has dedicated strokes for intake and exhaust, a two-stroke engine performs these actions simultaneously. 'Scavenging' is the specific process where the fresh air-fuel mixture (or just air in diesel engines) enters the cylinder and pushes out the burnt exhaust gases from the previous combustion cycle. This ensures the cylinder is cleared of waste gases and filled with a fresh charge for the next cycle. Analysis of other options: - Option (a) refers to 'Compression', which is a separate phase of the cycle. - Option (b) refers to 'Ignition' or 'Combustion'. - Option (d) refers to 'Lubrication', which is a maintenance process to reduce friction, not a cycle phase.

A car diary (also known as a vehicle logbook) is an official record used primarily in government departments and corporate organizations to track the utilization of a vehicle. Its primary purpose is to monitor fuel consumption, ensure the vehicle is used for authorized official purposes, and track maintenance intervals. 1. Why Option 'c' is correct: A standard car diary must record the date of the journey, the starting point, the destination (end location), and the odometer readings (start and end) to calculate the total distance traveled. This provides an audit trail for the vehicle's movement. 2. Why Option 'a' is incorrect: Horsepower is a technical specification of the engine and remains constant; it is not a daily variable to be recorded in a diary. 3. Why Option 'b' is incorrect: While some specialized transport logs might track passengers, a standard official car diary focuses on the vehicle's movement and mileage rather than the number of occupants. 4. Why Option 'd' is incorrect: Vehicle fitness is recorded in a 'Fitness Certificate' issued by the Regional Transport Office (RTO) after a formal inspection, not in the daily car diary.

A Vehicle History Sheet (also known as a vehicle maintenance log or service record) is a formal document used by fleet managers and engineers to track the lifecycle, maintenance, and repair history of a specific vehicle. 1. **Dates of Services (Option a):** Essential for tracking maintenance intervals and ensuring the vehicle is serviced according to the manufacturer's schedule. 2. **Types of repair done (Option b):** Critical for identifying recurring faults, tracking part replacements, and assessing the overall mechanical health of the vehicle. 3. **Name of workshop (Option d):** Necessary for accountability, warranty claims, and verifying that the work was performed by an authorized or qualified service provider. **Why Option c is correct:** 'Road condition during trips' is operational data typically recorded in a **Trip Sheet** or a **Driver's Log Book**, not a Vehicle History Sheet. The history sheet focuses on the physical state and maintenance of the machine itself, whereas road conditions are external environmental factors related to specific journeys.

BS-VI stands for 'Bharat Stage VI'. It is an emission standard instituted by the Government of India to regulate the output of air pollutants (such as nitrogen oxides, particulate matter, and carbon monoxide) from internal combustion engines. These standards are based on the European (Euro) emission standards. - Option (a) 'Bharat State' is incorrect as it refers to a political entity, not a technical standard. - Option (b) 'Bharat Standard' is a common misconception, but the official terminology used by the Ministry of Road Transport and Highways (MoRTH) is 'Stage'. - Option (d) 'Bureau of Standard' is incorrect; while the Bureau of Indian Standards (BIS) exists, the specific automotive emission nomenclature is 'Bharat Stage'.

Step-by-step reasoning: 1. Gas welding typically involves a fuel gas and an oxidizing agent (oxygen). 2. Acetylene (C2H2) is the most common fuel gas used due to its high flame temperature. 3. Acetylene is chemically unstable and highly explosive when mixed with air or oxygen, especially at pressures above 15 psi (approx 1 bar), where it can decompose violently without an external ignition source. This is why it is stored dissolved in acetone within porous masses in cylinders. 4. Oxygen (Option a) is an oxidizer; it supports combustion but is not explosive on its own. 5. Hydrogen (Option b) is flammable and explosive, but in the context of standard gas welding (Oxy-Acetylene welding), Acetylene is the primary gas noted for its extreme instability and specific handling requirements (like flash-back arrestors). 6. Nitrogen (Option c) is an inert gas and is not explosive.

A radiator is a heat exchanger used in the liquid cooling system of an internal combustion engine. Its primary purpose is to transfer heat from the liquid coolant (which has absorbed heat from the engine block) to the surrounding air. Step-by-step reasoning: 1. **Coolant (Option d):** This is the correct answer. Coolant (typically a mixture of water and ethylene glycol) circulates through the engine and then flows into the radiator to be cooled down before returning to the engine. 2. **Brake oil (Option a):** This is a hydraulic fluid used in the braking system to transmit force from the pedal to the brake calipers/cylinders; it is stored in a brake fluid reservoir, not a radiator. 3. **Engine oil (Option b):** This is a lubricant used to reduce friction between moving parts. It is stored in the oil pan (sump) and circulated by an oil pump. 4. **Gear oil (Option c):** This is a heavy-duty lubricant used in the transmission and differentials; it is contained within the gearbox or axle housing.

MPFI stands for Multi Point Fuel Injection. In this system, each cylinder has its own dedicated fuel injector located just before the intake valve. This allows for precise control of the fuel-air mixture for each individual cylinder, leading to better fuel efficiency, lower emissions, and improved engine performance compared to single-point injection or carburetors. Analysis of other options: - Option (a) 'Mechanical Petrol Fuel Injection' is incorrect as modern MPFI systems are electronically controlled (EFI). - Option (c) 'Manifold Pressure Fuel Injection' is incorrect; while manifold pressure is a sensor input (MAP sensor) used to calculate fuel delivery, it is not what MPFI stands for. - Option (d) 'Maximum Petrol Fuel Intake' is a nonsensical term in the context of fuel injection system nomenclature.

To determine which option is not a type of welding, we analyze each process: 1. **TIG Welding (Tungsten Inert Gas Welding):** This is a legitimate arc welding process that uses a non-consumable tungsten electrode to produce the weld. It is widely used for high-quality welds on stainless steel and aluminum. 2. **MIG Welding (Metal Inert Gas Welding):** This is a legitimate arc welding process where a consumable wire electrode is fed through a welding gun. It is known for its speed and efficiency in industrial applications. 3. **Gas Welding:** This is a legitimate welding process (such as Oxy-Acetylene welding) that uses the combustion of fuel gases and oxygen to create a flame that melts the base metal and filler rod. 4. **Lathe Welding:** A lathe is a machine tool used for machining (turning, facing, threading) by rotating a workpiece against a cutting tool. While welding can be performed on a part that is held in a lathe (for symmetry), 'Lathe Welding' is not a recognized category or process of welding in mechanical engineering. Therefore, option (d) is the correct answer as it describes a machine tool rather than a welding process.

A four-stroke internal combustion engine operates on a cycle consisting of four distinct piston strokes: 1. Suction (Intake): The piston moves from Top Dead Center (TDC) to Bottom Dead Center (BDC), drawing the air-fuel mixture (or air alone in diesel engines) into the cylinder. 2. Compression: The piston moves from BDC to TDC, compressing the charge to increase pressure and temperature. 3. Expansion (Power): The combustion of the fuel forces the piston from TDC to BDC, producing useful mechanical work. 4. Exhaust: The piston moves from BDC to TDC, pushing the combustion gases out of the cylinder. Scavenging, on the other hand, is the process of pushing exhaust gases out of the cylinder using a fresh charge of air or air-fuel mixture. This process is a characteristic feature of two-stroke engines, where the intake and exhaust functions happen simultaneously or in quick succession without a dedicated exhaust stroke. Therefore, scavenging is not a part of the standard four-stroke engine cycle.

A thermostat in a liquid cooling system acts as a temperature-controlled valve. Its primary function is to maintain the engine at its optimal operating temperature. When the engine is cold (during startup), the thermostat remains closed, preventing coolant from flowing to the radiator; this allows the engine to warm up quickly to reduce wear and improve efficiency. Once the coolant reaches a specific predetermined temperature, the thermostat opens, allowing the hot coolant to flow into the radiator to be cooled by air. Analysis of other options: - Option (a) is incorrect because the cooling fan speed is typically controlled by a fan switch, a sensor, or the engine's RPM (in belt-driven fans), not the thermostat. - Option (c) is incorrect because coolant pressure is managed by the radiator cap (pressure valve), not the thermostat. - Option (d) is incorrect because the water pump is lubricated by the coolant itself or internal bearings/seals, not by the thermostat.

TIG (Tungsten Inert Gas) welding, also known as Gas Tungsten Arc Welding (GTAW), uses a non-consumable electrode made of tungsten. The purpose of the electrode in TIG welding is solely to create the electric arc that melts the base metal; it does not melt into the weld pool. If filler metal is required, it is added separately by the welder. Analysis of other options: - (a) Consumable: This describes electrodes used in MIG (Metal Inert Gas) or SMAW (Shielded Metal Arc Welding), where the electrode melts to become part of the joint. - (b) Coated: This refers to electrodes used in SMAW (Stick welding), where a flux coating provides shielding gas and slag. - (d) Made of copper: Copper is too conductive and has a melting point too low for the arc temperatures required in TIG welding; tungsten is used because of its extremely high melting point.

In a petrol engine (which operates on the Spark Ignition or SI cycle), the air-fuel mixture is compressed within the cylinder. Unlike a diesel engine, which uses compression heat to ignite the fuel, a petrol engine requires an external source of ignition. The spark plug is an electrical device that delivers a high-voltage electric spark across a small gap at the end of the plug, which initiates the combustion of the compressed air-fuel mixture, driving the piston downward. Analysis of other options: - Option (a) is incorrect because the mixing of air and fuel is performed by the carburetor or fuel injectors. - Option (c) is incorrect because engine temperature is measured by a temperature sensor or thermocouple. - Option (d) is incorrect because the opening and closing of valves are controlled by the camshaft and valve train mechanism.

A Compression Ignition (C.I.) engine is an internal combustion engine where the ignition of the fuel is triggered by the heat generated from the high compression of air. In this cycle, only air is compressed to a very high pressure and temperature; fuel (typically diesel) is then injected into this hot air, causing it to ignite spontaneously without the need for an external spark. This is the fundamental operating principle of a Diesel Engine. Analysis of other options: - Option (a) Petrol Engine: These are Spark Ignition (S.I.) engines, where a spark plug is used to ignite a mixture of air and fuel. - Option (c) Steam Engine: This is an External Combustion engine where steam is generated in a separate boiler. - Option (d) Electric Engine: This is an electric motor, not an internal combustion engine, as it converts electrical energy into mechanical energy.

A Megger (short for mega-ohmmeter) is a specialized electrical instrument designed specifically to measure very high resistances, typically in the range of megohms (MΩ). Its primary application is to measure the insulation resistance of electrical components such as wires, cables, and motor windings to ensure that the insulation is intact and preventing leakage current. Why other options are incorrect: - Option (a) Breakdown voltage: This is the voltage level at which insulation fails completely. Measuring this requires a High Potential (Hi-Pot) tester, not a Megger, which measures resistance at a specific voltage rather than the failure point. - Option (c) Earth resistance: While some specialized earth testers look similar to meggers, earth resistance is typically measured using a dedicated Earth Tester (Ground Resistance Tester) which uses a different method (such as the fall-of-potential method) involving auxiliary spikes driven into the ground.

Sparking occurs during the switching off of a load due to the property of inductors to oppose sudden changes in current. According to Lenz's Law and the formula for induced voltage V = L(di/dt), when a switch is opened in a circuit with high inductance (L), the current (i) attempts to drop to zero almost instantaneously (dt is very small). This creates a very high rate of change of current, resulting in a large induced voltage (back EMF) across the switch contacts. If this voltage exceeds the dielectric strength of the air gap between the opening contacts, the air ionizes and becomes conductive, resulting in an electric arc or 'sparking'. Why other options are incorrect: - b. High impedance: Impedance is the total opposition to current; while it affects current flow, it is not the specific cause of the voltage spike during switching. - c. High resistance: Purely resistive loads do not store energy in a magnetic field and therefore do not produce significant sparking when switched off. - d. High Capacitance: While capacitors can cause sparking during switching (due to stored charge), the standard context for 'sparking when a load is switched off' in electrical engineering typically refers to inductive loads (like motors or transformers) because they generate a voltage spike to maintain current flow.

In elevator engineering, the rated speed is determined by the height of the building and the intended use of the lift. Residential elevators (used in low to mid-rise apartment buildings) typically operate at lower speeds to ensure passenger comfort and safety, and because the travel distance is relatively short. Standard industry ranges for residential/low-rise elevators generally fall between 0.5 m/s (for very low-rise/home lifts) and 2.5 m/s (for mid-rise residential complexes). Speeds above 2.5 m/s are typically reserved for high-rise commercial buildings or skyscrapers to reduce travel time. Therefore, option (b) provides the most comprehensive range that covers both basic residential lifts and those in larger residential complexes.

A one-way single pole switch (also known as a Single Pole Single Throw or SPST switch) is the simplest type of switch used in house wiring. It has two terminals: one for the incoming live wire and one for the outgoing wire to the load. Its primary function is to 'break' or 'make' the connection of a single conductor (the phase/live wire) to a single position (the load). - Option (a) is correct because the switch controls the flow of one wire (the live wire) to one specific destination/position (the light or appliance). - Option (b) is incorrect because controlling one wire to two positions would describe a selector switch or a change-over switch. - Option (c) and (d) are incorrect because a single pole switch does not control two wires simultaneously; controlling two wires (Live and Neutral) would require a double-pole switch.

An induction-type energy meter operates based on the interaction of magnetic fields produced by the voltage coil (pressure coil) and the current coil. The driving torque of the energy meter is proportional to the product of the voltage and the current (V × I). Specifically, the torque is proportional to the square of the voltage (V²) if the load is constant (since I = V/R). When the supply voltage increases beyond the rated value, the magnetic flux produced by the voltage coil increases. This leads to an increase in the driving torque acting on the aluminum disc, causing the disc to rotate faster than it would at the rated voltage. Consequently, the energy meter records more energy than is actually being consumed, meaning it runs 'fast'. Conversely, if the voltage were lower than the rated value, the meter would run 'slow'.

Step-by-step reasoning: 1. **Understanding Eddy Currents**: When a varying magnetic flux passes through a solid conductive core, it induces small circulating currents within the core material itself. These are known as eddy currents. 2. **The Problem**: These currents flow in loops and, due to the electrical resistance of the core material, they generate heat (I²R losses), which leads to energy inefficiency and potential overheating of the transformer. 3. **The Solution (Lamination)**: To prevent these currents from flowing in large loops, the core is constructed from thin sheets (laminations) of silicon steel, each coated with a thin layer of insulating varnish. 4. **Mechanism**: The insulation increases the electrical resistance between the sheets, effectively breaking the paths of the eddy currents and confining them to very small areas. This significantly reduces the total eddy current loss. Analysis of other options: - **Option (a)**: Copper losses occur in the windings (conductors), not the iron core. Lamination of the core has no effect on copper losses. - **Option (b)**: Hysteresis losses are caused by the friction of magnetic domains flipping during magnetization. These are reduced by using high-permeability materials like **Silicon Steel**, not by laminating the core. - **Option (d)**: Since lamination specifically targets eddy currents and not hysteresis losses, this option is incorrect.