Electric charge is measured in Coulombs (C). 1 Coulomb = charge carried by ~6.24×10¹⁸ electrons. Ampere is the unit of current, Volt of potential difference, Ohm of resistance.
Convex mirrors give a wider field of view (virtual, erect, diminished image) making them ideal for rear-view mirrors. Concave mirrors are used in vehicle headlights to produce parallel beams.
Sound is a mechanical (longitudinal) wave that requires a medium to travel. In vacuum, there are no particles, so sound cannot propagate. It travels fastest in solids and slowest in gases.
Speed of light c = 2.998×10⁸ m/s ≈ 3×10⁸ m/s. This is the universal constant used in Einstein's E=mc². Light takes ~8.3 minutes to travel from Sun to Earth.
F = kq₁q₂/r². Coulomb's Law describes electrostatic force between point charges. k = 9×10⁹ Nm²/C². Faraday's Law relates to electromagnetic induction, Ohm's Law to V=IR.
Power = Work/Time. Unit is Watt (W) = 1 Joule/second. Joule is the unit of energy/work, Newton of force, Pascal of pressure.
Diffraction is the bending of waves around obstacles or through slits. Reflection = bouncing back; Refraction = change of direction due to change in medium; Dispersion = splitting of white light into spectrum.
A transformer uses mutual induction — changing current in primary coil induces EMF in secondary coil. V₁/V₂ = N₁/N₂. Transformers only work with AC, not DC.
VIBGYOR — Violet has the highest frequency and shortest wavelength in visible spectrum. Red has lowest frequency and longest wavelength. f = c/λ, so shorter wavelength = higher frequency.
Barometer measures atmospheric pressure. Mercury barometer invented by Torricelli. Normal atmospheric pressure = 760 mm Hg = 1 atm = 101325 Pa. Hygrometer measures humidity.
In a series circuit, all components share the same current path. If one fails (open circuit), current stops flowing through the entire circuit. Parallel circuits don't have this problem — each branch is independent.
Frequency (f) = number of cycles per second. 1 Hz = 1 cycle/second. Named after Heinrich Hertz. Audible frequency range: 20 Hz to 20,000 Hz. Ultrasound > 20,000 Hz.
Fuse wire needs high resistance to generate heat quickly and low melting point to melt and break the circuit when excess current flows, protecting appliances. Common material: tin-lead alloy.
Myopia (near-sightedness) — image forms in front of retina. Concave (diverging) lens corrects this by diverging light rays before they enter the eye. Convex lens corrects hypermetropia (far-sightedness).
Ohm's Law: V = IR. Voltage (V) = Current (I) × Resistance (R). Formulated by Georg Simon Ohm. Materials obeying this law are called ohmic conductors.
Inertia is the tendency of a body to resist changes in its state. Newton's First Law is the Law of Inertia. Heavier objects have more inertia. When a bus brakes suddenly, passengers lurch forward due to inertia.
Pressure = Force/Area. SI unit = Pascal (Pa) = 1 N/m². Named after Blaise Pascal. 1 atm = 101325 Pa. Bar is a practical unit (1 bar = 10⁵ Pa).
Henri Becquerel discovered radioactivity in 1896 while studying uranium salts. Marie Curie coined the term "radioactivity" and discovered polonium and radium. Röntgen discovered X-rays.
For metallic conductors, resistance increases with temperature because increased atomic vibrations impede electron flow. For semiconductors (like thermistors), resistance DECREASES with temperature — opposite behavior.
Snell's Law: n₁sinθ₁ = n₂sinθ₂. It describes how light bends when passing from one medium to another. Kepler's Laws describe planetary motion; Boyle's Law: PV=constant (gas); Hooke's Law: spring force.
Loudness depends on amplitude (energy of vibration). Higher amplitude = louder sound. Pitch depends on frequency. Timbre (quality) depends on waveform. Loudness is measured in decibels (dB).
Light travels fastest in vacuum (3×10⁸ m/s). Speed in medium = c/n where n = refractive index. n(water)=1.33, n(glass)=1.5, n(diamond)=2.42. Higher n = slower light. Diamond slows light the most among common materials.
A stretched/compressed spring stores elastic potential energy = ½kx², where k is spring constant and x is displacement. This converts to kinetic energy when released (Hooke's Law principle).
Velocity is a vector quantity (has both magnitude and direction). Speed is the magnitude of velocity (scalar). Mass, temperature, energy, time, distance are all scalars. Force, displacement, acceleration are vectors.
Blue sky results from Rayleigh scattering — short wavelength blue light scatters more than red. Intensity of scattering ∝ 1/λ⁴. During sunrise/sunset, light travels farther through atmosphere, scattering blue away, leaving red/orange.
Terminal velocity is the constant speed reached when gravitational force equals drag (air resistance). Net force = 0, so acceleration = 0, velocity becomes constant. Parachutists reach terminal velocity ~55 m/s before deploying chute.
Voltmeter measures potential difference (voltage) and is connected in PARALLEL. Ammeter measures current and is connected in SERIES. Voltmeter has very high resistance to not disturb circuit.
Conduction = heat transfer through direct contact (solids). Convection = heat transfer through fluid movement. Radiation = heat transfer via electromagnetic waves (no medium needed). Sun heats Earth by radiation.
By convention, magnetic field lines exit from the North pole and enter the South pole outside the magnet. Inside the magnet, they run from South to North. Field lines never intersect each other.
Nuclear fission — splitting of heavy nuclei (U-235 or Pu-239) — releases enormous energy as heat, which converts water to steam to drive turbines. Nuclear fusion (H+H→He) powers the Sun but is not yet commercially viable.
Absolute zero = 0 K = -273.15°C. At this temperature, molecular motion theoretically stops completely. The Kelvin scale starts at absolute zero. T(K) = T(°C) + 273.15.
For a distinct echo, the reflected sound must reach the ear at least 0.1 second after the original. At sound speed ~340 m/s, the wall must be at least 340×0.1/2 = 17 m away. Human ear persistence of sound = 1/10th second.
An electric motor converts electrical energy into mechanical energy using the force on a current-carrying conductor in a magnetic field (F = BIL). Generator does the reverse — mechanical to electrical.
Candela (cd) is the SI base unit of luminous intensity. Lumen is luminous flux (total light output). Lux is illuminance (lumens per square metre). Candela measures how bright a source appears in a given direction.
Horizontal motion and vertical motion are independent. Both a horizontally thrown body and a dropped body experience the same vertical acceleration g. They hit the ground simultaneously. This demonstrates the principle of independence of motions.
Baking soda = Sodium bicarbonate (NaHCO₃). Na₂CO₃ = washing soda. NaCl = common salt. NaOH = caustic soda. Baking soda releases CO₂ when heated, causing baked goods to rise.
Metal + Acid → Salt + Hydrogen gas. E.g., Zn + H₂SO₄ → ZnSO₄ + H₂↑. Metals above hydrogen in reactivity series react with dilute acids to produce H₂ gas.
pH scale: 0–14. pH 7 = neutral (pure water). pH < 7 = acidic. pH > 7 = basic/alkaline. pH = -log[H⁺]. Blood pH = 7.35–7.45 (slightly alkaline). Lemon juice pH ≈ 2 (acidic).
Fluorine has electronegativity = 3.98 (Pauling scale), the highest of all elements. Electronegativity increases left→right and bottom→top in periodic table. Fluorine is in top-right corner (Period 2, Group 17).
Rust = Fe₂O₃.xH₂O (hydrated iron(III) oxide). It forms when iron reacts with oxygen and moisture. Rusting is an electrochemical process — saltwater accelerates it. Galvanizing (zinc coating) prevents rust.
Diamond (pure carbon in tetrahedral structure) is the hardest natural substance — 10 on Mohs scale. Graphite is also pure carbon but soft (pencil). Diamond is hard due to covalent bonding in 3D network. Used in cutting tools.
Acid rain is caused by SO₂ (sulphur dioxide) and NOₓ (nitrogen oxides) from burning fossil fuels. They react with water to form H₂SO₄ (sulphuric acid) and HNO₃ (nitric acid), lowering rain pH below 5.6.
Bleaching powder = Ca(OCl)Cl or CaOCl₂ (calcium hypochlorite and calcium chloride mixture). Made by passing Cl₂ over dry slaked lime Ca(OH)₂. Used for bleaching, disinfecting water.
Atomic number (Z) = number of protons. Mass number (A) = protons + neutrons. In a neutral atom, number of electrons = number of protons = Z. Carbon: Z=6, A=12 (6 protons, 6 neutrons).
Natural rubber = cis-polyisoprene (polymer of isoprene, C₅H₈). Vulcanization (treating with sulfur) hardens rubber. Synthetic rubbers include Neoprene and Buna-S. Rubber is obtained from Hevea brasiliensis tree.
Chlorophyll contains Magnesium (Mg) at its centre in a porphyrin ring. Haemoglobin (blood) contains Iron (Fe). Vitamin B₁₂ contains Cobalt (Co). These metal-organic complexes are essential in biology.
Plaster of Paris = CaSO₄.½H₂O (hemi-hydrate of calcium sulphate). When mixed with water, it sets hard forming CaSO₄.2H₂O (gypsum). Used in setting broken bones, making moulds, and construction.
Incandescent bulbs are filled with inert gas (Argon or mixture of Nitrogen + Argon) to prevent filament oxidation and slow its evaporation. Vacuum bulbs had shorter life. Neon is used in advertising tubes (orange-red glow).
Common salt = NaCl (sodium chloride). It is an ionic compound. Sodium carbonate = Na₂CO₃ (washing soda). Sodium bicarbonate = NaHCO₃ (baking soda). Sodium hydroxide = NaOH (caustic soda).
Ozone (O₃) in the stratosphere absorbs harmful UV radiation (especially UV-B and UV-C). CFC gases (chlorofluorocarbons) deplete ozone. Ozone hole was first reported over Antarctica in 1985. Montreal Protocol (1987) banned CFCs.
Earth's crust composition: Oxygen (46.6%) > Silicon (27.7%) > Aluminium (8.1%) > Iron (5%) > Calcium > Sodium > Potassium > Magnesium. Oxygen is most abundant, silicon is second (mostly as SiO₂).
Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (yeast/anaerobic). Discovered by Louis Pasteur. Used in bread making (CO₂ causes dough to rise), beer, wine, yogurt production.
Indian coins are made of Cupronickel (copper-nickel alloy) or stainless steel. ₹1, ₹2, ₹5 coins = ferritic stainless steel. ₹10 coins = bimetallic (cupronickel + steel). Brass = Cu+Zn; Bronze = Cu+Sn.
Vitamin C = Ascorbic acid. Retinol = Vitamin A. Riboflavin = Vitamin B₂. Tocopherol = Vitamin E. Vitamin C deficiency causes scurvy. Found in citrus fruits, amla.
CO₂ is used in fire extinguishers because it doesn't support combustion and is denser than air, smothering flames. Also used: dry powder (NaHCO₃), foam (AFFF). Water extinguishers NOT used on electrical/oil fires.
Petroleum (crude oil) is a complex mixture of hydrocarbons (compounds of C and H only). Fractional distillation separates it into: LPG, petrol (gasoline), kerosene, diesel, lubricating oil, paraffin wax, bitumen.
Vinegar contains acetic acid (CH₃COOH, 4–8%). Citric acid is in lemons/oranges. Lactic acid is in sour milk/curd. Tartaric acid is in tamarind. Formic acid is in ant stings.
Stainless steel = Fe + Cr (at least 10.5%) + Ni. Chromium forms a passive Cr₂O₃ layer preventing rust. Used in cutlery, cookware, surgical instruments. Brass = Cu+Zn; Solder = Pb+Sn.
Heavy water = D₂O where D is deuterium (²H, hydrogen with 1 neutron). Used to slow down neutrons in CANDU-type nuclear reactors. Density slightly higher than regular water (1.105 g/mL vs 1.0 g/mL).
Nitrous oxide (N₂O) is called laughing gas — used as an anaesthetic and produces euphoria. Discovered by Joseph Priestley. NO = nitric oxide; NO₂ = nitrogen dioxide (brown gas, air pollutant); NH₃ = ammonia (pungent).
Calcination = heating ore in limited air to remove water, CO₂, volatile impurities. Roasting = heating sulphide ores in excess air. Smelting = reduction of ore to metal in blast furnace. CaCO₃ → CaO + CO₂ (calcination).
Haber Process: N₂ + 3H₂ ⇌ 2NH₃. Catalyst = finely divided iron + K₂O (promoter) + Al₂O₃. Conditions: 400–500°C, 200 atm pressure. Vanadium pentoxide is catalyst for Contact process (H₂SO₄).
CO₂ is the primary greenhouse gas (contributes ~63% of enhanced greenhouse effect). Others: Methane (CH₄), N₂O, CFCs, water vapour. Greenhouse gases trap outgoing infrared radiation, warming Earth.
Bronze = Cu + Sn (tin, ~10%). Used since ancient times (Bronze Age). Brass = Cu + Zn. German silver = Cu + Zn + Ni. Duralumin = Al + Cu + Mg + Mn (aircraft). Steel = Fe + C.
Ionic dissociation: NaCl → Na⁺ + Cl⁻ (in water). Ions are solvated by water molecules. Ionization refers to gas-phase removal of electrons. Precipitation = formation of insoluble solid from solution reaction.
CaC₂ (calcium carbide) releases acetylene (ethylene) gas when exposed to moisture, which ripens fruit artificially. This practice is harmful — CaC₂ may contain arsenic traces. Natural ripening agent = ethylene gas (C₂H₄).
Noble (inert) gases: He, Ne, Ar, Kr, Xe, Rn — all in Group 18. They have complete valence shells (8 electrons, except He with 2), making them chemically inert. Group 17 = Halogens (F, Cl, Br, I). Group 1 = Alkali metals.
Milk of magnesia = Mg(OH)₂ suspension. Used as antacid (neutralizes stomach acid) and mild laxative. Magnesium sulphate = MgSO₄ (Epsom salt). Baking soda also neutralizes stomach acidity (NaHCO₃).
The ovum (female egg cell) is the largest human cell — visible to naked eye (~0.1 mm diameter). The longest cell is the sciatic nerve cell/neuron (can be up to 1 metre). Smallest cell = lymphocytes (~5 µm).
Insulin (from beta cells of islets of Langerhans, pancreas) lowers blood glucose by promoting glycogen synthesis. Glucagon (from alpha cells) raises blood sugar. Deficiency of insulin = Type 1 Diabetes mellitus.
Friedrich Miescher first isolated DNA (he called it "nuclein") from white blood cells in 1869. Watson and Crick proposed the double helix structure in 1953 (using Franklin's X-ray data). Mendel = father of genetics.
Blood group O (O negative) = universal donor (no A or B antigens). Blood group AB = universal recipient (no anti-A or anti-B antibodies). ABO system discovered by Karl Landsteiner (Nobel Prize 1930).
Mitochondria produce ATP (adenosine triphosphate) through cellular respiration (Krebs cycle, oxidative phosphorylation). Have their own DNA. Nucleus = control centre; Ribosomes = protein synthesis; Chloroplast = photosynthesis in plants.
Liver produces bile (stored in gallbladder), which emulsifies fats in the small intestine. Liver also: detoxifies blood, produces albumin, stores glycogen/iron, converts ammonia to urea.
Genetics studies how traits are inherited and how they vary. Founded by Gregor Mendel (Laws of Inheritance). Ecology = study of organisms and environment; Physiology = functioning of organisms; Taxonomy = classification.
Malaria is caused by Plasmodium (protozoan parasite) — P. falciparum (most deadly), P. vivax, P. malariae, P. ovale. Transmitted by female Anopheles mosquito. Discovered by Ronald Ross. Treated with quinine/chloroquine.
Transpiration is loss of water vapour through stomata (mainly leaves). It creates suction force that pulls water up from roots (transpiration pull). ~90% of water absorbed by roots is lost via transpiration.
Humans have 46 chromosomes (23 pairs) in diploid (2n) somatic cells. 23 = haploid (n) number in gametes (sperm/egg). Sex chromosomes: XX (female), XY (male). Trisomy 21 = Down syndrome (47 chromosomes).
Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light + chlorophyll). Light reactions in thylakoid membranes; Calvin cycle in stroma. Chloroplast contains chlorophyll (green pigment) that absorbs light energy.
Vitamin D deficiency → Rickets (softening of bones in children), Osteomalacia (adults). Scurvy = Vitamin C deficiency. Anaemia = Iron deficiency. Pellagra = Vitamin B₃ (Niacin) deficiency. Vitamin D is synthesized in skin by sunlight.
Nephron is the structural and functional unit of kidney (~1 million per kidney). Each nephron has Bowman's capsule, glomerulus, proximal/distal tubules, Loop of Henle. Alveolus = gas exchange unit in lung. Neuron = nerve cell.
Liver is the largest gland and largest internal organ (1.2–1.5 kg). Also the largest exocrine gland. Skin is the largest organ overall. Liver functions: bile production, detoxification, glycogen storage, protein synthesis.
Anaerobic respiration in yeast (fermentation): Glucose → Ethanol + CO₂. In animal muscles: Glucose → Lactic acid (causes cramps). Aerobic respiration: Glucose + O₂ → CO₂ + H₂O + 38 ATP (much more energy).
Cerebellum coordinates movement, balance, and posture. Cerebrum = thinking, consciousness, voluntary actions. Medulla oblongata = involuntary actions (breathing, heartbeat). Hypothalamus = body temperature, hunger, sleep regulation.
Alexander Fleming discovered penicillin in 1928 from Penicillium mold. Nobel Prize 1945 (Fleming, Florey, Chain). Edward Jenner = smallpox vaccine. Louis Pasteur = germ theory. Robert Koch = identified TB bacillus.
Haemoglobin (Hb) in RBCs contains iron (Fe²⁺) in its haem group — binds O₂. Iron deficiency → anaemia. Chlorophyll contains Mg. Haemocyanin (in molluscs/crustaceans) contains copper — their blood is blue.
Salivary amylase (ptyalin) in saliva begins starch digestion in mouth, breaking starch into maltose. Pepsin (stomach) = protein digestion. Lipase = fat digestion. Trypsin (pancreas) = protein digestion in small intestine.
Dengue is caused by dengue virus (DENV 1-4), transmitted by Aedes aegypti mosquito. Also transmits Chikungunya and Zika. Anopheles transmits malaria. Sandfly transmits Kala-azar (leishmaniasis). Culex transmits filariasis.
Deamination removes the amino (-NH₂) group from amino acids in the liver. Ammonia produced is converted to urea (urea cycle) and excreted by kidneys. Glycolysis = breakdown of glucose; Lipolysis = breakdown of fats.
BCG (Bacillus Calmette-Guérin) vaccine prevents tuberculosis (TB), caused by Mycobacterium tuberculosis. Given to newborns. TB treated with DOTS (Directly Observed Treatment Short-course) — Rifampicin, Isoniazid, etc.
Platelets (thrombocytes) are cell fragments that initiate blood clotting. They aggregate at wound site, release clotting factors, triggering fibrin mesh formation. Thrombocytopenia (low platelets) causes excessive bleeding.
Carl Linnaeus developed binomial nomenclature (genus + species) system. Father of taxonomy. "Systema Naturae" (1735). Aristotle = first systematic biologist/father of biology. Darwin = evolution theory.
Vitamin K is essential for synthesis of clotting factors (prothrombin). Deficiency causes excessive bleeding. Vitamin A = vision. Vitamin C = antioxidant, collagen. Vitamin D = calcium absorption. Fat-soluble vitamins: A, D, E, K.
AIDS (Acquired Immunodeficiency Syndrome) is caused by HIV (Human Immunodeficiency Virus), a retrovirus. HIV attacks CD4+ T lymphocytes (helper T cells), weakening immunity. Transmitted by blood, sexual contact, mother to child. No cure — managed with ART.
Adrenaline (epinephrine) is released by adrenal medulla during stress/emergency. Increases heart rate, blood pressure, blood glucose, dilates pupils and airways. Called "hormone of emergency." Insulin = blood sugar regulation. Thyroxine = metabolism.
Plasmodium undergoes sexual reproduction (gametogony, sporogony) in female Anopheles mosquito (definitive host). Asexual reproduction (schizogony) occurs in human liver and RBCs (intermediate host). Ronald Ross discovered this cycle.
Myopia (short-sightedness) — corrected by concave lens; Hypermetropia (long-sightedness) — corrected by convex lens; Astigmatism — corrected by cylindrical lens. Presbyopia = age-related far-sightedness — reading glasses (bifocal).
Pituitary gland (hypophysis) is the "master gland" — controls other endocrine glands via trophic hormones (TSH, ACTH, FSH, LH, GH, ADH). Located at base of brain. Size of a pea. Controlled by hypothalamus.
Connective tissues include: bone, cartilage, blood, adipose (fat) tissue, tendons, ligaments. They connect, support, and protect other tissues. Bones have osteocytes; cartilage has chondrocytes; blood has RBCs, WBCs, platelets.
Homo sapiens = "wise man" in Latin. Classified by Carl Linnaeus. Pan troglodytes = chimpanzee. Homo erectus and Homo habilis = extinct human ancestors. Full classification: Kingdom Animalia → Phylum Chordata → Class Mammalia → Order Primates → Family Hominidae → Genus Homo → Species sapiens.