UPSC CSE Prelims
Physics and Applied Technology Previous Year Questions (PYQs)

Detailed Explanation:

Option A — Correctly Matched ✓ CG Power (in partnership with Renesas Electronics & STARS Microelectronics) is setting up an OSAT facility in Sanand, Gujarat.

Option B — Correctly Matched ✓ Tata Semiconductor Assembly and Test Pvt. Ltd. (TSAT) is establishing a greenfield semiconductor assembly and test facility in Jagiroad, Assam — a major industrial investment for Northeast India.

Option C — Incorrectly Matched ✗ The HCL-Foxconn Joint Venture (India Chip Pvt. Ltd.) OSAT facility is being set up in Jewar, Uttar Pradesh (Yamuna Expressway Industrial Development Authority region) — NOT Madhya Pradesh. It will manufacture display driver chips.

Option D — Correctly Matched ✓ SicSem Pvt. Ltd. is establishing a Silicon Carbide (SiC) semiconductor plant in Bhubaneswar, Odisha — India's first commercial compound semiconductor fab.

Quick Memory Table:

Detailed Explanation:

Statement 1 — Correct. DHRUV64 is the third chip fabricated under the Digital India RISC-V (DIR-V) Programme, in the following sequence:

The DIR-V Programme aims to build an indigenous portfolio of RISC-V-based microprocessors to reduce India's dependence on imported chips and foreign intellectual property.

Statement 2 — Correct. DHRUV64 is India's first homegrown 1.0 GHz, 64-bit dual-core microprocessor, developed by C-DAC under the Ministry of Electronics and Information Technology (MeitY). It is built on the open-source RISC-V instruction set architecture, which ensures:

• No proprietary licensing fees
• Technological sovereignty for India

Key Facts to Remember:

• Programme: DIR-V (Digital India RISC-V)
• Developer: C-DAC under MeitY
• Architecture: Open-source RISC-V
• Significance: 3rd chip, 1st 64-bit dual-core at 1.0 GHz

Detailed Explanation:

Answer: Option 3 — All three

An accelerometer is a sensor that measures acceleration forces, including changes in velocity, sudden movements, and changes in orientation (tilt). All three actions described in the question require the detection of acceleration changes or orientation shifts, making the accelerometer essential for their functioning.

✅ Action 1 – Car Crash Detection: Accelerometers detect the rapid deceleration during a collision, triggering immediate airbag deployment through the crash detection system.

✅ Action 2 – Laptop Free Fall Detection: Accelerometers sense the characteristic acceleration pattern of free fall (near-zero resistance), immediately parking the hard drive heads to prevent damage upon impact.

✅ Action 3 – Smartphone Tilt Detection: Accelerometers continuously monitor the device's orientation relative to gravity, enabling automatic display rotation between portrait and landscape modes.

📝 Short Notes: Accelerometer Applications

• Definition: An accelerometer is an electromechanical device that measures acceleration forces, both static (gravity) and dynamic (movement, vibration, shock).
• Working Principle: It detects changes in velocity, tilt, rotation, and vibration by measuring the displacement of a proof mass on springs when subjected to acceleration.
• Types: MEMS (Micro-Electro-Mechanical Systems) accelerometers are most commonly used in consumer electronics due to their small size and low power consumption.
• Automotive Safety: Used in airbag deployment systems, electronic stability control (ESC), anti-lock braking systems (ABS), and rollover detection.
• Consumer Electronics: Smartphones (screen rotation, step counting, gesture recognition), laptops (hard drive protection), gaming controllers (motion sensing), and fitness trackers.
• Industrial Applications: Vibration monitoring in machinery, structural health monitoring of buildings and bridges, and seismic activity detection.
• Aviation and Navigation: Inertial navigation systems, flight stabilization, and drone orientation control.

Detailed Explanation:

Answer: Option 1 — 1 only

Carbon fibres are extensively used in manufacturing components for automobiles and aircraft due to their exceptional strength-to-weight ratio, high stiffness, and lightweight properties. Statement 1 is correct as these materials are crucial in aerospace and automotive industries for reducing weight and improving fuel efficiency.

✅ Statement 1 – Correct: Carbon fibres are indeed used in manufacturing automobile and aircraft components due to their superior mechanical properties and lightweight nature.

❌ Statement 2 – Incorrect: Carbon fibres can be recycled through various methods including mechanical recycling (breaking down into smaller pieces), chemical recycling (dissolving resin to extract fibres), and thermal recycling (pyrolysis to recover fibres), though the technology is still evolving.

📝 Short Notes: Carbon Fibres

• Composition: Made from organic polymers consisting of long strings of carbon atoms bonded together in crystalline alignment
• Key Properties: High tensile strength, low weight (5 times lighter than steel), high stiffness, high temperature tolerance, low thermal expansion, and chemical resistance
• Manufacturing Process: Produced through carbonization of precursor materials like polyacrylonitrile (PAN), pitch, or rayon at high temperatures (1000-3000°C)
• Applications: Aerospace (aircraft fuselage, wings), automotive (racing cars, luxury vehicles), sports equipment (bicycles, tennis rackets), wind turbine blades, and medical devices
• Recycling Methods: Mechanical (chopping/milling), thermal/pyrolysis (burning off resin at 450-700°C), chemical (solvolysis using solvents), and electrochemical processes
• Challenges: High production cost, brittleness (low impact resistance), difficulty in recycling compared to metals, and specialized manufacturing requirements
• Environmental Consideration: While recyclability was limited earlier, modern recycling technologies are making carbon fibre composites more sustainable with recovered fibres retaining 90-95% of original properties

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three technologies—CCTV, RFID, and WLAN—are classified as short-range communication devices. Short-range technologies typically operate within a few centimeters to a few hundred meters, unlike long-range technologies such as cellular networks or satellite communication.

✅ Closed-Circuit Television (CCTV) – Short-Range: CCTV systems use cables or wireless connections with limited range, typically confined to a building or specific premises, operating within tens to hundreds of meters.

✅ Radio Frequency Identification (RFID) – Short-Range: RFID uses radio waves for identification and tracking, with typical reading ranges from a few centimeters to about 10 meters depending on the tag type (passive, active, or semi-passive).

✅ Wireless Local Area Network (WLAN/Wi-Fi) – Short-Range: WLAN networks typically operate within 20-100 meters indoors and up to 300 meters outdoors, making them short-range compared to wide-area networks like cellular or satellite systems.

📝 Short Notes: Short-Range Communication Technologies

• Short-range vs Long-range: Short-range technologies operate within localized areas (centimeters to hundreds of meters), while long-range technologies like cellular networks (kilometers) and satellite communication (global coverage) serve wider geographical areas.
• Power consumption: Short-range devices typically consume less power, making them suitable for battery-operated applications.
• Data rate: Generally, shorter ranges allow for higher data transfer rates (e.g., Wi-Fi offers Mbps to Gbps speeds).
• Applications: Short-range technologies are ideal for home automation, personal devices, local networking, surveillance, and proximity-based services.

Detailed Explanation:

Answer: Option 4 — 2 and 3

This question tests understanding of nanoparticles, their natural occurrence, applications, and potential safety concerns. Statement 1 is incorrect as nanoparticles occur naturally through various processes, while statements 2 and 3 are correct regarding their use in cosmetics and potential environmental risks.

❌ Statement 1 – Incorrect: Nanoparticles exist naturally in the environment through volcanic eruptions, forest fires, ocean spray, and biological processes (e.g., viruses, protein complexes).

✅ Statement 2 – Correct: Nanoparticles of metallic oxides like zinc oxide (ZnO) and titanium dioxide (TiO₂) are commonly used in sunscreens and cosmetics for UV protection and improved texture.

✅ Statement 3 – Correct: Many nanoparticles from commercial products can enter the environment and may pose health risks due to their ability to penetrate biological barriers and accumulate in organs.

📝 Short Notes: Nanoparticles

• Definition: Particles with at least one dimension between 1-100 nanometers (nm)
• Natural Sources: Volcanic ash, sea spray, forest fires, mineral weathering, and biological entities (viruses, ferritin)
• Cosmetic Applications: Zinc oxide and titanium dioxide nanoparticles in sunscreens provide broad-spectrum UV protection without visible white residue
• Other Applications: Drug delivery, electronics, catalysis, water purification, antibacterial coatings
• Safety Concerns: High surface area-to-volume ratio allows interaction with biological systems; can cross blood-brain barrier and cell membranes; potential for bioaccumulation
• Environmental Impact: Persistence in environment, toxicity to aquatic organisms, unknown long-term effects on ecosystems
• Regulation: Many countries are developing specific guidelines for nanomaterial safety assessment in consumer products

Detailed Explanation:

Answer: Option 4 — Speed of light is always same.

Astronomical distances are measured in light-years because the speed of light in a vacuum is a universal constant (approximately 299,792 km/s). This constant nature makes it a reliable and standardized unit for measuring the vast distances in space. A light-year represents the distance light travels in one year, providing a practical scale for cosmic distances.

❌ Statement A – Incorrect: Distances between stellar bodies do change due to orbital motion, stellar evolution, and galactic movements; this is not why light-years are used as a unit.

❌ Statement B – Incorrect: While gravity is fundamental, the gravitational effects of stellar bodies vary with mass and distance changes; this has no bearing on the choice of light-year as a distance unit.

❌ Statement C – Incorrect: Light does not always travel in a straight line; it bends around massive objects due to gravitational lensing, as predicted by Einstein's General Theory of Relativity.

✅ Statement D – Correct: The speed of light in a vacuum is constant at approximately 3 × 10⁸ m/s, making it an ideal standard for measuring astronomical distances.

📝 Short Notes: Astronomical Distance Measurements

• Light-Year: The distance light travels in one year in a vacuum (approximately 9.46 trillion kilometers or 5.88 trillion miles).
• Astronomical Unit (AU): The average distance from Earth to the Sun (approximately 150 million km); used for measuring distances within the solar system.
• Parsec: Another unit for astronomical distances, equal to about 3.26 light-years; commonly used by professional astronomers.
• Speed of Light (c): A fundamental physical constant equal to 299,792,458 meters per second in vacuum; remains constant regardless of the observer's motion or the source's motion.
• Gravitational Lensing: The bending of light around massive objects due to gravity, predicted by Einstein's General Theory of Relativity and observed around galaxies and black holes.

Detailed Explanation:

Answer: Option 3 — 1 and 3 Only

In a pressure cooker, the cooking temperature depends on the internal pressure, which determines the boiling point of water. The area of the hole in the lid and the weight of the lid regulate how much pressure builds up inside the cooker, thereby controlling the cooking temperature. The flame temperature only affects the rate of heating, not the maximum temperature achieved.

✅ Statement 1 – Correct: The size of the hole in the lid regulates steam release; a larger hole allows more steam to escape, reducing internal pressure and thus lowering the cooking temperature.

❌ Statement 2 – Incorrect: The temperature of the flame affects only the rate of heating, not the final cooking temperature, which is determined by the internal pressure of the cooker.

✅ Statement 3 – Correct: A heavier weight on the lid requires higher internal pressure to lift it, allowing steam to escape only when higher pressure is reached, which increases the boiling point and thus the cooking temperature.

📝 Short Notes: Pressure Cooker Mechanism

• Principle: Pressure cookers work on the principle that increasing pressure raises the boiling point of water above 100°C.
• Normal Boiling Point: At atmospheric pressure (1 atm), water boils at 100°C.
• In Pressure Cooker: Pressure can reach 15 psi (about 2 atm), raising the boiling point to approximately 121°C.
• Pressure Regulation: The weight (regulator) on the vent controls the maximum pressure by allowing steam to escape when pressure exceeds a threshold.
• Vent Hole Size: The area of the vent hole determines how easily steam can escape, affecting pressure buildup.
• Cooking Time: Higher temperature due to increased pressure reduces cooking time significantly.
• Flame Role: The flame intensity affects how quickly the cooker reaches operating pressure, not the final cooking temperature.

Detailed Explanation:

Answer: Option 3 — 1, 3 and 4 only

Carbon nanotubes (CNTs) are cylindrical nanostructures with unique properties that make them suitable for biomedical applications including drug delivery, biosensing, and under certain conditions, biodegradation. Statement 2 is incorrect as CNTs cannot be reliably made into functional artificial blood capillaries—this application remains experimental and lacks validated clinical use.

✅ Statement 1 – Correct: CNTs can be functionalized with drugs and antigens, making them effective carriers for targeted delivery in the human body due to their ability to cross biological membranes.

❌ Statement 2 – Incorrect: While CNTs have been explored in tissue engineering scaffolds, they cannot be made into functional artificial blood capillaries as these require precise biological compatibility, flexibility, and permeability that CNTs alone cannot replicate.

✅ Statement 3 – Correct: CNTs possess high surface-to-volume ratio and unique electrical properties, making them ideal for biochemical sensors that detect biomolecules like glucose, proteins, and DNA with high sensitivity.

✅ Statement 4 – Correct: Research has shown that CNTs can be biodegraded by oxidative enzymes such as myeloperoxidase (MPO) found in human neutrophils, though biodegradability depends on CNT type, structure, and surface functionalization.

📝 Short Notes: Carbon Nanotubes

• Structure: Cylindrical nanostructures composed of rolled-up sheets of graphene, with diameters in nanometers and lengths up to micrometers.
• Types: Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).
• Properties: Exceptional mechanical strength, high electrical and thermal conductivity, high surface area, and ability to be functionalized.
• Biomedical Applications: Drug delivery systems, gene therapy carriers, biosensors, tissue engineering scaffolds, and imaging contrast agents.
• Drug Delivery: Can be functionalized to carry therapeutic agents and target specific cells, improving drug efficacy and reducing side effects.
• Biosensors: Used in electrochemical and optical sensors for detecting glucose, cholesterol, DNA, proteins, and pathogens with high sensitivity.
• Biodegradability Debate: Some studies show enzymatic degradation by peroxidases, but biodegradability varies with CNT structure, functionalization, and environmental conditions; persistence in biological systems remains a concern.
• Challenges: Potential toxicity, biocompatibility issues, aggregation in biological fluids, and lack of standardized methods for large-scale production and functionalization.

Detailed Explanation:

The correct answer is 1, 2 and 3 (Option 3). Einstein's General Theory of Relativity states that gravity bends light, matter curves space-time, and its equations also allow an expanding universe, which was later confirmed by observations.

General Theory of Relativity (1915) explains gravity as the curvature of space-time caused by mass and energy. It predicts phenomena like gravitational lensing, black holes, gravitational waves, and the expanding universe.

Detailed Explanation:

Answer: Option 3 — 1, 2 and 3

✅ Statement 1 – Correct: OLEDs use thin films of organic compounds that can be deposited on flexible plastic or metal foil substrates, unlike LCDs which require rigid glass panels. This enables bendable and foldable displays.

✅ Statement 2 – Correct: The inherent flexibility of OLED technology allows fabrication of roll-up displays that can be embedded in clothing, wearables, and other flexible surfaces—applications impossible with rigid LCD technology.

✅ Statement 3 – Correct: OLED pixels emit light independently without requiring a backlight, and the organic layers can be made semi-transparent. This enables creation of transparent displays where the screen is see-through when not displaying content, unlike LCDs which are always opaque due to their backlight and liquid crystal structure.

All three statements correctly identify key advantages of OLED over LCD technology.

Detailed Explanation:

Answer: Option 1 — Observation and understanding of the Universe

All four terms are fundamental concepts in cosmology and theoretical physics. Event Horizon is the boundary around a black hole beyond which nothing can escape its gravitational pull. Singularity refers to a point of infinite density and gravity, such as at the center of a black hole or the initial state of the Big Bang. String Theory is a theoretical framework attempting to unify all fundamental forces of nature by describing particles as vibrating strings. Standard Model is the established theory in particle physics describing fundamental particles and three of the four forces (excluding gravity). These concepts are central to understanding the structure, origin, and evolution of the Universe, making Option 1 the correct answer.

Detailed Explanation:

✅ Statement 1 – Correct: Nanoparticles enable targeted drug delivery by carrying drugs directly to diseased cells, minimizing side effects and enhancing treatment efficacy.

✅ Statement 2 – Correct: Nanocarriers deliver genetic material (DNA/RNA) into specific cells, making nanotechnology crucial for gene therapy to treat genetic disorders.

Detailed Explanation:

✅ Statement 1 – Correct: The Higgs boson discovery confirms the Higgs field mechanism that explains why elementary particles acquire mass through interaction with this field.

❌ Statement 2 – Incorrect: Matter teleportation (transferring matter without traversing physical space) is not related to the Higgs boson; this particle explains mass, not quantum teleportation or matter transport technologies.

❌ Statement 3 – Incorrect: The Higgs boson is a fundamental particle in the Standard Model of physics unrelated to nuclear fission fuels; it does not improve fuel efficiency or reactor technology.

Detailed Explanation:

1. Size of the sun at dusk – Optical illusion: The sun appears larger near the horizon due to the moon illusion, a psychological effect where our brain misinterprets distance cues, though its actual angular size remains constant.

2. Colour of the sun at dawn – Optical illusion: The sun appears red/orange because its light travels through more atmosphere, causing Rayleigh scattering that removes blue light, creating a perceived color change.

3. Moon being visible at dawn – NOT an illusion: This is a real astronomical event where the moon's orbital position allows it to be visible during daylight hours.

4. Twinkle of stars – Optical illusion: Stars don't actually twinkle; their light is refracted by turbulent atmospheric layers, causing rapid brightness fluctuations.

5. Polestar being visible – NOT an illusion: The Pole Star (Polaris) is genuinely visible due to its alignment with Earth's rotational axis, making it appear stationary.

Answer: Option 3 (1, 2 and 4) are optical illusions.