General Science — UPSC Prelims Study Notes
Overview
General Science in UPSC Prelims tests your basic understanding of physics, chemistry, and biology at the 10th-standard level, along with awareness of recent scientific and technological developments. Unlike specialised science papers, this section does not require deep subject expertise—it focuses on conceptual clarity and the ability to connect science with everyday life, government programmes, and current affairs.
High-scoring areas include space technology (ISRO missions), health and diseases, biotechnology, and emerging technologies like AI and quantum computing. The key is to understand principles rather than memorise formulae, and to stay updated with science news.
This topic rewards candidates who read science sections of newspapers regularly and can apply basic scientific reasoning to eliminate wrong options.
Key Concepts
- Newton's Laws of Motion govern all mechanical phenomena: inertia, F = ma, and action-reaction pairs explain everything from rocket propulsion to why passengers lurch forward when a bus brakes.
- Energy cannot be created or destroyed, only transformed (Law of Conservation of Energy). This underpins power generation, metabolic processes, and climate science.
- Acids donate H⁺ ions; bases donate OH⁻ ions. pH scale runs 0–14; below 7 is acidic, above 7 is basic. Human blood pH is slightly basic (7.35–7.45).
- Cell is the basic unit of life. Prokaryotes (bacteria) lack a nucleus; eukaryotes (plants, animals, fungi) have membrane-bound organelles.
- DNA carries genetic information in a double-helix structure. Genes code for proteins. Mutations cause genetic disorders and also drive evolution.
- Vaccines stimulate the immune system to produce antibodies without causing disease—either using weakened pathogens, inactivated viruses, or mRNA (as in COVID-19 vaccines).
- Nuclear fission (splitting heavy atoms like Uranium-235) powers reactors; nuclear fusion (combining light atoms like hydrogen) powers the sun and is the goal of future clean energy.
- Satellites orbit based on Kepler's laws. Geostationary satellites (36,000 km altitude) appear stationary over Earth and are used for communication and weather monitoring.
Formulas / Key Facts
| Concept | Key Fact |
|---|---|
| Speed of light | 3 × 10⁸ m/s in vacuum |
| Speed of sound | ~340 m/s in air at 20°C |
| Atmospheric pressure | 1 atm = 101.3 kPa |
| Human body temperature | 37°C (98.6°F) |
| Blood groups | A, B, AB, O (based on antigens); Rh factor (+/-) |
| DNA bases | Adenine-Thymine, Guanine-Cytosine pairing |
| Photosynthesis equation | 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂ |
| India's nuclear programme | Three-stage: Uranium → Plutonium → Thorium |
Important Numbers to Remember:
- Ozone layer: 15–35 km altitude (stratosphere)
- Radioactive half-life of Carbon-14: ~5,730 years (used in carbon dating)
- Human genome: ~3 billion base pairs, ~20,000 genes
Worked Examples
Example 1: Why does ice float on water? Water expands when it freezes, making ice less dense (0.92 g/cm³) than liquid water (1 g/cm³). Since density of ice < density of water, ice floats. This anomalous expansion of water is crucial for aquatic life surviving winters.
Example 2: How do vaccines work? A vaccine introduces a weakened/inactivated pathogen or its genetic material (mRNA) into the body. The immune system recognises foreign antigens, produces antibodies, and creates memory cells. When the actual pathogen attacks later, the immune system responds rapidly, preventing disease.
Example 3: Why is the sky blue? Sunlight contains all colours. When it enters the atmosphere, shorter wavelengths (blue, violet) scatter more due to Rayleigh scattering by gas molecules. Our eyes are more sensitive to blue than violet, so the sky appears blue. At sunset, light travels through more atmosphere, scattering away blue and leaving red/orange.
Common Mistakes
- Confusing nuclear fission and fusion → Fission splits heavy atoms (used in current reactors and bombs); fusion combines light atoms (powers the sun, not yet commercially viable on Earth).
- Believing antibiotics work on viruses → Antibiotics target bacteria only. Viral infections (flu, COVID-19) require antivirals or vaccines. Misuse leads to antimicrobial resistance.
- Mixing up conduction, convection, and radiation → Conduction: heat transfer through direct contact (metal spoon in hot soup). Convection: heat transfer through fluid movement (boiling water). Radiation: heat transfer without medium (sunlight reaching Earth).
- Assuming all radiation is harmful → Ionising radiation (X-rays, gamma rays) can damage DNA. Non-ionising radiation (radio waves, visible light) is generally safe at normal levels.
- Confusing weather and climate → Weather is short-term atmospheric conditions; climate is long-term average patterns. Climate change refers to shifts in these long-term patterns.
Quick Reference
- ISRO launch vehicles: PSLV (polar satellites, reliable workhorse), GSLV (heavier payloads, cryogenic engine), LVM3 (Chandrayaan-3, Gaganyaan)
- Vitamins: A, D, E, K are fat-soluble (stored in body); B-complex and C are water-soluble (excess excreted)
- Greenhouse gases (descending warming potential per molecule): SF₆ > HFCs > N₂O > CH₄ > CO₂
- Blood group compatibility: O-negative is universal donor; AB-positive is universal recipient
- India's thorium reserves are among world's largest—basis for third stage of nuclear programme
- CRISPR-Cas9: Gene-editing tool that can cut DNA at specific locations; revolutionising medicine and agriculture