Past Questions

Step-by-step reasoning: 1. The question asks for a component that converts mechanical energy into electrical energy. 2. An Alternator is an electrical generator that is driven by the engine's crankshaft via a belt (mechanical energy). It uses electromagnetic induction to produce alternating current (AC), which is then rectified to direct current (DC) to charge the battery and power the vehicle's electrical systems. 3. Analysis of other options: (a) ECU (Engine Control Unit) is a computer that manages engine functions; it consumes electrical energy to process data. (b) Ignition Coils are transformers that step up low voltage to high voltage to create a spark; they do not generate primary electrical energy from mechanical motion. (d) A Solenoid is an electromagnetic switch that converts electrical energy into linear mechanical motion. Therefore, the Alternator is the only component that performs the requested conversion.

In arc welding, flux is a chemical cleaning agent, flowing agent, or shielding agent. Its primary functions are: 1. To prevent the molten weld pool from reacting with atmospheric oxygen and nitrogen (shielding), which prevents porosity and oxidation. 2. To react with and remove impurities and oxides from the surface of the base metal, forming a liquid slag that floats to the top of the weld pool. While flux can contribute to arc stability (option a), its 'main' or fundamental metallurgical function is the removal of impurities and the protection of the weld pool from oxidation. Option c is incorrect because flux is not used for electrical insulation, and option d is incorrect because flux coating does not increase the functional diameter of the electrode core.

Lubricants are substances introduced between two moving surfaces to reduce friction and wear. Their primary functions include: 1. Reducing Friction (Option a): By creating a thin film between surfaces, lubricants prevent direct metal-to-metal contact, thereby reducing friction. 2. Cooling (Option b): Lubricants absorb heat generated by friction and carry it away from the moving parts to a sump or cooler, helping to maintain optimal operating temperatures. 3. Sealing (Option c): In many systems (like piston rings in an engine), the lubricant creates a seal to prevent the leakage of gases or fluids between components. 4. Cleaning: They carry away contaminants and wear particles from the contact surfaces. Heating (Option d) is NOT a function of a lubricant. In fact, lubricants are designed to prevent the excessive heating that occurs due to friction. While some lubricants may be pre-heated for better flow in cold climates, the purpose of the lubrication system itself is to mitigate heat, not generate it.

To determine the advantage of a petrol engine (Spark Ignition - SI) over a diesel engine (Compression Ignition - CI), we must compare their design and operational characteristics: 1. **Initial Cost (Option c):** Petrol engines operate at lower compression ratios compared to diesel engines. Because they do not need to withstand the extreme pressures associated with high compression ratios, the engine components (cylinder block, piston, connecting rods) can be made of lighter, less expensive materials. Additionally, they do not require the heavy-duty high-pressure fuel injection pumps found in diesel engines. Therefore, the initial manufacturing cost of a petrol engine is lower. This is the correct answer. 2. **Performance (Option a):** 'Performance' is subjective. While petrol engines offer better acceleration and higher RPMs (power-to-weight ratio), diesel engines provide superior torque and efficiency. Thus, it is not a definitive universal advantage. 3. **Cost of Fuel (Option b):** Historically and generally, diesel fuel is often priced similarly to or lower than petrol in various markets, but more importantly, diesel engines are more thermally efficient, meaning they use less fuel for the same amount of work. Petrol is not cheaper in terms of energy output per unit cost. 4. **Running Cost (Option d):** Diesel engines have higher thermal efficiency and better fuel economy, leading to lower running costs per kilometer/hour compared to petrol engines. Therefore, lower running cost is an advantage of the diesel engine, not the petrol engine.

A feeler gauge is a precision measurement tool consisting of a series of thin steel strips (blades) of varying, calibrated thicknesses. It is specifically designed to measure the width of small gaps, clearances, or the distance between two mating parts (such as the gap between spark plug electrodes or valve clearances in an engine). Why other options are incorrect: - b. Diameter: Measured using tools like Vernier calipers, micrometers, or bore gauges. - c. Height: Measured using height gauges or calipers. - d. Radius: Measured using radius gauges or a spherometer.

In gas welding (specifically Oxy-Acetylene welding), gas cylinders are color-coded to ensure safety and prevent the accidental mixing of incompatible gases. 1. Oxygen Cylinders: According to international and Indian standards (such as IS codes), oxygen cylinders are painted Black. This allows technicians to quickly identify the oxidizing agent. 2. Acetylene Cylinders: These are typically painted Maroon or Red to distinguish the fuel gas from the oxygen. Analyzing the options: - Option (a) Blue: Not the standard color for oxygen in gas welding. - Option (b) Black: Correct. This is the standard identification color for Oxygen cylinders. - Option (c) Orange: Not used for oxygen cylinders. - Option (d) Red: This is typically used for Acetylene or other flammable fuel gases.

In internal combustion engines, cooling systems are fundamentally classified into two main types based on the medium used to dissipate heat from the engine block: 1. Air Cooling System: This system relies on the flow of air over the engine surfaces (often aided by fins to increase surface area) to remove heat. It is commonly used in small engines, motorcycles, and some aircraft engines. 2. Liquid Cooling System: This system uses a coolant (typically a mixture of water and antifreeze) that circulates through channels (water jackets) around the cylinders and is then cooled by a radiator. This is the standard system for most modern automobiles and heavy-duty engines. Since all other cooling methods (such as forced air or pressurized liquid) are variations of these two primary categories, the correct answer is 'Two Types'.

A vehicle log book is an official record used primarily in government departments (like the PWD) and commercial organizations to ensure accountability and proper upkeep of assets. 1. **Vehicle Usage:** It records the date, time, destination, and purpose of every trip to prevent unauthorized use of the vehicle. 2. **Mileage:** It tracks the odometer readings (starting and ending) for each journey to calculate total distance traveled and fuel efficiency. 3. **Maintenance:** It serves as a history log for services, repairs, oil changes, and tire replacements, ensuring the vehicle remains roadworthy and safe. Why other options are incorrect: - Option (a) is irrelevant as radio stations are not tracked in a vehicle log book. - Option (b) is incorrect because spare keys are stored in a secure locker or with a fleet manager, not recorded in a log book. - Option (d) is incorrect because driving licenses are verified by authorities or during hiring; the log book records the driver's name, but its primary purpose is not to 'check' the license.

Daily vehicle maintenance (often called a 'pre-trip inspection') focuses on safety-critical items and fluids that fluctuate or deplete quickly. 1. **Check coolant (Option a):** Essential for daily checks to prevent engine overheating, especially in varying weather conditions. 2. **Check cleanliness of mirror (Option b):** A critical safety requirement for visibility and road safety, performed every time a vehicle is started. 3. **Check Tyre Pressure (Option c):** While some modern vehicles have TPMS, a visual or gauge check of tyre pressure is a standard daily/regular safety practice to ensure traction and fuel efficiency. 4. **Check Gear oil (Option d):** Gear oil is a long-term lubricant. Unlike engine oil or coolant, gear oil levels do not fluctuate daily and are typically checked during scheduled periodic maintenance (e.g., every 10,000 to 50,000 km) or when a leak is suspected. It is not part of a standard daily checklist.

A liquid cooling system is designed to regulate the engine's temperature by circulating a coolant (water or ethylene glycol) to absorb heat. 1. Radiator (Option a): This is a critical component that acts as a heat exchanger, transferring heat from the coolant to the ambient air. 2. Thermostat (Option b): This is a valve that regulates the flow of coolant based on temperature, ensuring the engine reaches its optimal operating temperature quickly and stays there. 3. Water Pump (Option c): This is the mechanical pump that forces the coolant to circulate through the engine block and the radiator. 4. Air filter (Option d): An air filter is part of the engine's intake system, not the cooling system. Its purpose is to remove contaminants from the air before it enters the combustion chamber. Therefore, it is not a component of the liquid cooling system.

The primary function of an oil pump in an internal combustion engine is to draw oil from the sump (oil pan) and force it under pressure to the various moving parts of the engine, such as the crankshaft, camshaft, and piston pins. This ensures a continuous hydrodynamic film of oil between sliding surfaces to reduce friction and wear. Analysis of other options: - Option (a) is incorrect because the oil is stored in the oil sump or oil pan, not the pump. - Option (b) is incorrect because the filtration of oil is performed by the oil filter. - Option (d) is incorrect because while circulating oil helps carry heat away from components, the actual cooling of the oil is handled by the oil cooler (heat exchanger) or through convection in the sump.

Step-by-step reasoning: 1. Soldering small electronic components requires precise heat control and a localized heat source to avoid damaging sensitive semiconductor devices or melting plastic circuit boards. 2. An Electric Soldering Iron is specifically designed for this purpose; it uses a heating element to maintain a constant temperature at the tip, allowing the user to melt solder precisely on a small joint. 3. Analysis of other options: (a) Gas Torches and (b) Blow Lamps produce excessive, uncontrolled heat (open flames) that would instantly destroy electronic components and burn the PCB. (d) A Welding Gun is used for joining heavy metals through fusion (melting the base metal), which is an entirely different process from soldering (which uses a filler metal with a lower melting point) and is far too powerful for electronics. Therefore, the Electric Soldering Iron is the only appropriate tool.

In gas welding (such as Oxy-Acetylene welding), the blow pipe is the device where the fuel gas and the oxidizer (oxygen) are mixed in a controlled proportion and then ignited at the tip to produce a high-temperature flame. This assembly is technically and commonly referred to as the 'Welding Torch'. Reasoning for other options: - a. Mixer: While the torch contains a mixing chamber, the entire assembly (including the handle and nozzle) is called the torch, not just a 'mixer'. - c. Regulator: The regulator is the device attached to the gas cylinder to reduce the high pressure of the gas to a usable working pressure; it is not the blow pipe. - d. Cylinder: The cylinder is the storage vessel for the compressed gases, not the tool used to direct the flame.

Step-by-step reasoning: 1. The question asks for the term describing a fluid's resistance to flow. 2. Viscosity is defined as the internal friction of a fluid that opposes the relative motion between its layers (shear stress). A fluid with high viscosity (like honey) resists flow more than a fluid with low viscosity (like water). 3. Evaluating other options: (a) Density is the mass per unit volume of a substance, not its resistance to flow. (b) Flash point is the lowest temperature at which a liquid gives off enough vapor to ignite in air. (d) Pour point is the lowest temperature at which a liquid (usually oil) remains fluid and can still be poured. Therefore, option 'c' is the only correct technical term for resistance to flow.

A vehicle repair estimate is a document that outlines the projected costs required to restore a vehicle to working condition or to perform scheduled maintenance. 1. **Labor Charges (Option a):** These are essential as they cover the technician's time and expertise required to perform the repair. 2. **Spare parts Cost (Option b):** This is a primary component of any estimate, covering the cost of replacing worn-out or damaged components (e.g., brake pads, filters, belts). 3. **Paint and Material Cost (Option d):** In the case of bodywork or surface restoration, the cost of paint, primers, and consumables is standard in a repair estimate. 4. **Fuel Charges (Option c):** Fuel is an operational expense (running cost), not a repair cost. While a small amount of fuel might be used for testing a vehicle after repair, it is not listed as a line item in a standard repair estimate. Fuel is consumed during the usage of the vehicle, whereas repair estimates focus on the restoration of the asset.

In a four-stroke internal combustion engine, one complete thermodynamic cycle consists of four distinct piston strokes: 1. Intake (Suction), 2. Compression, 3. Power (Expansion), and 4. Exhaust. Each single stroke of the piston (moving from Top Dead Center to Bottom Dead Center, or vice versa) corresponds to 180 degrees of crankshaft rotation. Calculation: - 1st stroke (Intake): 180° - 2nd stroke (Compression): 180° - 3rd stroke (Power): 180° - 4th stroke (Exhaust): 180° Total rotation = 180° * 4 = 720°. Since one full revolution of the crankshaft is 360°, 720° / 360° = 2 full revolutions. Therefore, the crankshaft must rotate twice to complete one full cycle of a four-stroke engine.

In an air-cooled engine, heat is transferred from the combustion chamber to the cylinder walls and head via conduction. To remove this heat efficiently, the engine relies on convection (air flowing over the surfaces). According to Newton's Law of Cooling, the rate of heat transfer is directly proportional to the surface area. By adding 'fins' (thin metal projections), the total surface area exposed to the cooling air is significantly increased, allowing more heat to be dissipated into the atmosphere and preventing the engine from overheating. Why other options are incorrect: - b: While fins add material, their primary design purpose is thermal management, not structural reinforcement. - c: A heat sink is a general component that absorbs heat; while fins act as part of a heat sink system, their specific 'function' in this design is the expansion of surface area to facilitate dissipation. - d: While proper cooling prevents efficiency loss due to overheating, the fins themselves do not directly improve the combustion process or fuel efficiency.

Step-by-step reasoning: 1. **Analysis of Option (a):** Diesel engines operate at higher compression ratios compared to petrol engines. According to the laws of thermodynamics, a higher compression ratio leads to higher thermal efficiency. Additionally, diesel fuel has a higher energy density per gallon/liter than gasoline, resulting in higher fuel efficiency (better mileage). 2. **Analysis of Option (b):** This is incorrect. Diesel engines are known for providing *higher* torque at lower RPMs due to their high compression ratios and the nature of the diesel combustion process, making them ideal for heavy-duty hauling. 3. **Analysis of Option (c):** This is not an 'advantage'. While diesel engines may produce lower CO2 per kilometer due to efficiency, they typically produce higher NOx and particulate matter (soot). Regardless, higher emissions are never considered an advantage. 4. **Analysis of Option (d):** This is incorrect. Diesel engines are *more* robust (sturdier) than petrol engines because they must be built to withstand the much higher cylinder pressures associated with compression ignition. Conclusion: The only positive attribute listed that correctly describes a Diesel engine relative to a Petrol engine is its higher fuel efficiency.

A vehicle survey report is a formal technical document used to document the current state of a vehicle. Its primary purposes include: 1. Condition Assessment: Determining if the vehicle is roadworthy or requires maintenance. 2. Damage Evaluation: In the event of an accident, a survey is conducted to quantify the extent of damage for insurance claims or repair estimates. 3. Valuation: Establishing the current market or book value of the asset for accounting, disposal, or insurance purposes. Why other options are incorrect: - Option (a): While a survey report may be used as a supporting document during a sale, the report's purpose is the evaluation itself, not the act of selling. - Option (b): Vehicle taxes are typically assessed based on engine capacity, fuel type, weight, or age (registration details), not through a physical survey report. - Option (d): Fuel efficiency is improved through mechanical tuning, aerodynamic changes, or driving habits, not by preparing a documentation report.

In gas welding (specifically Oxy-Acetylene welding), cylinders are color-coded to ensure safety and prevent the accidental mixing of gases. 1. Acetylene Gas: The standard color for acetylene cylinders is Maroon (or sometimes reddish-brown). Acetylene is a highly unstable gas, and the maroon color serves as a universal identifier for this fuel gas. 2. Oxygen Gas: Oxygen cylinders are typically painted Black (in some standards) or Blue/Green (depending on the regional standard, such as ISO or ASME), but in the context of standard engineering exams, Oxygen is often associated with Black or Blue. Comparing the options: - Black: Typically used for Oxygen (in certain standards). - Yellow: Often used for Argon or other specific industrial gases. - Maroon: The standard color for Acetylene. - Blue: Often used for Oxygen or other specialty gases. Therefore, the correct color for an acetylene gas cylinder is Maroon.

Step-by-step reasoning: 1. The objective is to identify the tool used to measure the outer diameter of a cylindrical object. 2. Analysis of options: - (a) Vernier Height Gauge: Used primarily for measuring the height of objects or marking off heights from a reference surface. - (b) Micrometer (specifically the Outside Micrometer): Designed specifically to measure external dimensions, such as the outer diameter of a cylinder or the thickness of a plate, with very high precision (typically up to 0.01mm or 0.001mm). - (c) Dial Gauge: Used for checking the roundness (ovality) of a cylinder, flatness of a surface, or comparing dimensions against a standard; it does not measure the absolute diameter directly. - (d) Bevel Protractor: Used for measuring or marking angles. 3. Conclusion: The Micrometer is the standard instrument for measuring the outer diameter of cylindrical objects.

A Spark Ignition (S.I.) engine is an internal combustion engine where the fuel-air mixture is ignited by an electric spark produced by a spark plug. Petrol (gasoline) is the primary fuel used in these engines because of its volatility and ability to mix with air to form a combustible mixture. Analysis of options: - Option (a) Diesel Engine: These are Compression Ignition (C.I.) engines, where fuel is ignited by the heat of highly compressed air, not by a spark. - Option (b) Petrol Engine: Correct. These utilize spark plugs for ignition. - Option (c) Steam Engine: This is an External Combustion engine where steam is generated in a boiler outside the cylinder. - Option (d) Electric Engine: This is an electrical machine (motor) that converts electrical energy into mechanical energy; it is not an internal combustion engine.

Brazing is a joining process where a filler metal is melted and drawn into the joint by capillary action. To ensure a strong bond, a flux is used to prevent the formation of oxides on the base metal surfaces and to promote the wetting of the filler metal. 1. **Borax (Sodium Borate)**: This is the most common and widely used flux in brazing, especially for copper and steel. It melts at a relatively low temperature and effectively dissolves metal oxides, providing a clean surface for the filler metal to bond with. 2. **Rosin**: This is primarily used as a flux in soft soldering (especially for electronics), not brazing, as it cannot withstand the higher temperatures required for brazing. 3. **Zinc Chloride**: While used in some soldering fluxes (acid fluxes), it is generally too corrosive and not the standard 'common' flux for general brazing applications compared to borax. 4. **Lime**: Calcium oxide (lime) is not used as a flux in brazing; it is more commonly associated with metallurgy in smelting or construction materials.

In lubrication systems, the primary requirement is to move a viscous fluid (oil) at a constant flow rate and high pressure to ensure all moving parts of an engine or machine are coated. 1. Gear Pumps (Correct): These are positive displacement pumps. They are highly preferred for lubrication systems because they can handle high-viscosity fluids, provide a steady flow regardless of pressure changes, and are robust and simple to manufacture. 2. Centrifugal Pumps (Incorrect): These are dynamic pumps used primarily for water or low-viscosity fluids. They are inefficient for thick oils and cannot maintain a constant flow against varying pressure loads. 3. Diaphragm Pumps (Incorrect): These are typically used for dosing chemicals or handling corrosive/slurry fluids; they are not suitable for the continuous, high-pressure flow required in engine lubrication. 4. Piston Pumps (Incorrect): While they are positive displacement pumps, they are generally too complex, expensive, and bulky for standard lubrication systems, being reserved for high-pressure hydraulic systems instead.

Gas welding (specifically Oxy-fuel welding) requires a fuel gas and an oxidizing agent (oxygen) to produce a high-temperature flame capable of melting metals. 1. **Acetylene (C2H2)** is the most commonly used fuel gas because it produces the highest flame temperature (approximately 3,160°C to 3,500°C) among the common fuel gases. This high temperature allows for faster melting and better penetration of the metal. 2. **Oxygen (O2)** acts as the supporter of combustion, allowing the fuel gas to burn intensely. Comparing other options: - **Hydrogen and Oxygen**: While used in some specialized applications, the flame temperature is lower than acetylene, and hydrogen is more expensive and harder to store. - **Propane and Oxygen**: Propane is used for heating or brazing, but its flame temperature is significantly lower than acetylene, making it less effective for fusion welding of steel. - **Methane and Oxygen**: Methane has a very low flame temperature and is not suitable for industrial gas welding.