🔬 SCIENCE & TECHNOLOGY — TEXTBOOK DEPTH (Line-by-Line, Every Sub-Topic)

The deep-dive companion to the S&T revision note. Covers Physics → Chemistry → Biology & Health → Space → Defence & Nuclear → Biotech → Digital & Emerging Tech. In the modern Prelims, S&T is ~70–80% current affairs — this file is the static base that makes the news comprehensible.

PART 1 — PHYSICS (concepts with applications)

1.1 Mechanics

Newton's laws: (1) inertia (a body stays at rest/uniform motion unless a force acts — why you lurch when a bus brakes); (2) F = ma; (3) action–reaction (rocket propulsion, gun recoil).
Momentum = mass × velocity (conserved in collisions); work = force × displacement; power = work/time; energy — kinetic (½mv²) and potential (mgh); conservation of energy.
Gravitation: weight = mg; weightlessness in orbit is free fall, not the absence of gravity; escape velocity from Earth ≈ 11.2 km/s.
Pressure & fluids: P = F/A; Archimedes' principle (buoyancy — floating ships); Pascal's law (hydraulic brakes/lifts); Bernoulli's principle (aeroplane lift, a spinning ball's swing); surface tension (droplets, capillary rise); viscosity.

1.2 Heat, light & sound

Heat transfer: conduction (solids), convection (fluids — land/sea breeze), radiation (no medium — the Sun's heat; a thermos blocks all three). Water's high specific heat moderates coastal climate; latent heat (why steam burns worse than boiling water).
Optics: reflection (concave mirrors in headlights, convex in rear-view mirrors); refraction (a bent stick in water, mirages, twinkling of stars, apparent sunrise before actual); dispersion (rainbow — VIBGYOR); scattering (Rayleigh) — the blue sky and red sunrise/sunset (danger signals are red because red scatters least and travels farthest); total internal reflection (optical fibres, a diamond's sparkle). Vision defects: myopia (concave lens), hypermetropia (convex lens), presbyopia, cataract.
Sound: a mechanical wave — needs a medium (no sound in a vacuum); speed solids > liquids > gases (~343 m/s in air); audible 20 Hz–20 kHz; infrasound (elephants, quakes) and ultrasound (SONAR, medical imaging); echo, Doppler effect (a passing siren's pitch change).

1.3 Electricity, magnetism & modern physics

Ohm's law V = IR; series vs parallel (household wiring is parallel); fuse & earthing (safety); electromagnetic induction (Faraday) — the basis of the generator, transformer, and induction stove; AC vs DC (AC is transmitted over long distances via transformers).
Electromagnetic spectrum (increasing frequency/energy): radio → microwave → infrared → visible → ultraviolet → X-ray → gamma.
Modern physics: radioactivity (alpha/beta/gamma; half-life; carbon dating); nuclear fission (splitting a heavy nucleus → reactors, bombs) vs fusion (combining light nuclei → the Sun, hydrogen bomb, ITER — cleaner but needs extreme conditions); semiconductors, superconductors (zero resistance below a critical temperature), lasers, LEDs.

PART 2 — CHEMISTRY

Atomic structure: protons, neutrons, electrons; atomic number vs mass number; isotopes (same protons, different neutrons — U-235/U-238, C-14) vs isobars.
Periodic trends: across a period, atomic size decreases and electronegativity increases; down a group, the reverse.
Bonding: ionic (electron transfer — NaCl), covalent (sharing — water, CO₂), metallic, and hydrogen bonding (water's high boiling point, ice floating).
Acids, bases & salts: the pH scale (0–14; 7 neutral, <7 acidic, >7 basic); applications — antacids, lime for acidic soil, tooth decay below pH 5.5, baking & washing soda, plaster of Paris, bleaching powder.
Metals & non-metals: the reactivity series; corrosion/rusting (needs oxygen + moisture; prevented by galvanising, painting, alloying); alloys (steel = Fe + C; stainless steel adds Cr/Ni; brass = Cu + Zn; bronze = Cu + Sn).
Carbon & materials: catenation; allotropes — diamond (hardest), graphite (conducts, a lubricant), fullerene, graphene (single layer, exceptional strength/conductivity), carbon nanotubes; polymers/plastics (thermoplastic vs thermosetting), biodegradable vs non-biodegradable; soaps/detergents (micelle formation).

PART 3 — BIOLOGY & HEALTH (highest static yield)

3.1 Cell & molecular biology

Organelles: nucleus (DNA), mitochondria ("powerhouse", ATP), chloroplast (photosynthesis; magnesium-based chlorophyll), ribosome (protein synthesis), lysosome ("suicide bag"), Golgi, ER, vacuole. Prokaryotes (no true nucleus — bacteria) vs eukaryotes.
Central dogma: DNA → RNA → protein (transcription then translation). Photosynthesis releases oxygen; respiration is essentially the reverse (releases ATP). Mitosis (growth) vs meiosis (gametes, halves chromosomes, creates variation).
Genetics: genes, alleles, dominant/recessive, mutation; DNA is the hereditary material.

3.2 Human physiology

Digestive (enzymes — amylase, pepsin, trypsin; liver, pancreas), circulatory (four-chambered heart, double circulation; arteries vs veins; blood groups A/B/AB/O + Rh — O⁻ universal donor, AB⁺ universal recipient; haemoglobin has iron), respiratory (alveoli, gas exchange), excretory (kidney → nephron; dialysis), nervous (neuron, reflex arc; cerebrum-thinking, cerebellum-balance, medulla-involuntary).
Endocrine (hormone → gland → disorder): insulin → pancreas → diabetes; thyroxine → thyroid → goitre (needs iodine); adrenaline ("fight or flight"); growth hormone → pituitary ("master gland").

3.3 Nutrition, diseases & immunity

Deficiency diseases: Vitamin A → night blindness; B1 → beriberi; B3 → pellagra; B12 → anaemia; C → scurvy; D → rickets (osteomalacia in adults); K → poor clotting; iron → anaemia; iodine → goitre; protein → kwashiorkor, protein-calorie → marasmus.
Diseases by pathogen: bacterial (TB, cholera, typhoid, tetanus), viral (dengue, COVID, hepatitis, polio, rabies), protozoan (malaria — Plasmodium; spread by the female Anopheles), fungal, and vector-borne (dengue — Aedes; filariasis).
Immunity: innate vs acquired; active (vaccine — long-lasting) vs passive (ready antibodies — quick, short); herd immunity; vaccine types — live-attenuated, inactivated, subunit, mRNA, viral-vector.

PART 4 — SPACE TECHNOLOGY

Orbits: LEO (Low Earth Orbit — remote sensing, ISS), geostationary (~36,000 km, fixed over one point — communication/weather), polar / sun-synchronous (remote sensing, consistent lighting), Lagrange points (L1–L5, gravitationally stable — Aditya-L1 at L1).
Launch vehicles: PSLV (the "workhorse" — polar/sun-synchronous, and famous multi-satellite launches), GSLV (heavier, cryogenic upper stage), LVM3/GSLV-Mk III (heaviest — Chandrayaan/Gaganyaan), and the SSLV (small satellites).
ISRO milestones: Aryabhata (first satellite, 1975); Chandrayaan-1 (found water on the Moon); Mangalyaan/MOM (Mars, first attempt success); Chandrayaan-3 (soft landing near the lunar south pole); Aditya-L1 (solar observation); Gaganyaan (human spaceflight); the NavIC regional navigation system; and applications in agriculture, disaster management, communication and mapping (via Bhuvan). IN-SPACe / NSIL enable private participation.

PART 5 — DEFENCE & NUCLEAR

Missiles: ballistic (a parabolic trajectory, powered only initially — the Agni and Prithvi series) vs cruise (powered throughout, low-flying — BrahMos, supersonic); Akash (surface-to-air), Nag (anti-tank), Astra (air-to-air). The nuclear triad (land, air, sea-based delivery) and ballistic-missile defence.
Nuclear policy: India's "No First Use" doctrine and credible minimum deterrence; NPT & CTBT (India is a non-signatory), the NSG, and the India–US civil nuclear deal.
Nuclear energy: a three-stage programme (Pressurised Heavy Water Reactors → Fast Breeder Reactors → thorium-based, given India's large thorium reserves); reactors at Tarapur, Kudankulam, Kalpakkam; fusion research (ITER).

PART 6 — BIOTECHNOLOGY

Tools: recombinant DNA, PCR (DNA amplification), CRISPR-Cas9 (precise gene editing), cloning, stem cells, tissue culture.
Applications: GM crops (Bt cotton — bollworm resistance; Golden Rice — vitamin A), gene therapy, mRNA vaccines, monoclonal antibodies, biofuels, biofertilisers.
Health biotech: diagnostics (ELISA, RT-PCR), personalised medicine, the Human Genome Project.
Regulation & ethics: the GEAC (genetic engineering approval), biosafety (the Cartagena Protocol), bioethics, and biopiracy.

PART 7 — DIGITAL & EMERGING TECHNOLOGY

Computing & AI: Artificial Intelligence / Machine Learning (narrow vs general; generative AI), big data, cloud computing, edge computing, the Internet of Things (IoT).
Connectivity: 5G/6G, optical fibre, satellite internet.
Distributed & secure tech: blockchain (a distributed, immutable ledger — cryptocurrencies, CBDC/the digital rupee), cyber security.
Quantum tech: quantum computing (qubits, superposition, entanglement), quantum communication (unhackable keys) — the National Quantum Mission.
Digital Public Infrastructure: Aadhaar, UPI, DigiLocker, CoWIN, ONDC, and Account Aggregator; the DPDP Act 2023 (data protection); semiconductors (the India Semiconductor Mission).
Green tech: green hydrogen (electrolysis using renewables), advanced batteries and EVs, solar/wind, and carbon capture.

📚 References & Further Reading

The static deep-dive series is now complete for the Prelims-heavy subjects (Polity, History, Geography, Economy, Environment, Science & Tech). Art & Culture's revision note is already highly detailed, table-driven and visual — the ideal format for that subject.