Tamil Nadu SSLC Science cheat sheet

Newton's first law: a body stays at rest or in uniform motion unless acted on by a net external force; this defines inertia.

Newton's second law: F = ma; the acceleration is along the net force and inversely proportional to mass.

Newton's third law: forces occur in equal and opposite pairs acting on two different bodies, so they never cancel on one body.

Momentum p = mv; impulse J = F·t = change in momentum, useful for collisions and catching a ball by moving hands back.

Conservation of linear momentum holds when net external force is zero: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂.

Weight W = mg with g ≈ 9.8 m s⁻² on Earth; mass is constant, weight changes with location.

Friction: static friction adjusts up to a maximum μsN; kinetic friction equals μkN and opposes sliding.

Rocket propulsion and recoil of a gun are explained by momentum conservation, not by Newton's third law alone.

Circular motion needs a centripetal force F = mv²/r directed towards the centre; no outward 'centrifugal' force exists in an inertial frame.

Laws of reflection: angle of incidence equals angle of reflection, and incident ray, reflected ray and normal lie in one plane.

Plane mirror image is virtual, erect, laterally inverted, same size, and as far behind the mirror as the object is in front.

Spherical mirror formula: 1/f = 1/v + 1/u with f = R/2; sign convention: distances measured from pole, against incident light negative.

Magnification m = −v/u for mirrors and m = v/u for lenses; |m| > 1 means enlarged image.

Snell's law: n₁ sin i = n₂ sin r; refractive index n = c/v, so light slows in a denser medium.

Total internal reflection occurs when light travels from denser to rarer medium and i exceeds the critical angle C, where sin C = 1/n.

Lens formula: 1/f = 1/v − 1/u; power P = 1/f (in metres), unit dioptre; converging lens has positive power.

Convex lens: object beyond 2F gives real, inverted, diminished image; object within F gives virtual, erect, magnified image.

Dispersion through a prism occurs because refractive index differs with wavelength; violet bends most, red least.

Ohm's law: V = IR at constant temperature; resistance R = ρL/A, so longer and thinner wires have more resistance.

Series: same current, R = R₁ + R₂ + …; parallel: same voltage, 1/R = 1/R₁ + 1/R₂ + … .

Electrical power P = VI = I²R = V²/R; energy consumed in kWh = power in kW × time in hours.

Fuse is connected in the live wire; it melts when current exceeds rating, protecting the circuit.

Domestic wiring is parallel so each appliance gets full 230 V and can be switched independently; earth wire gives safety.

Magnetic field around a straight conductor forms concentric circles; right-hand thumb rule gives field direction.

Solenoid with current behaves like a bar magnet; field inside is uniform and strength increases with current and turns per unit length.

Fleming's left-hand rule gives force on a current-carrying conductor; Fleming's right-hand rule gives induced current direction.

Electromagnetic induction: changing magnetic flux through a coil induces emf; AC generator converts mechanical energy to electrical energy.

Modern periodic law: properties are periodic functions of atomic number; the table is arranged in 18 groups and 7 periods.

Period number equals the number of electron shells; group number relates to valence electrons for main-group elements.

Across a period, atomic radius decreases and ionisation energy, electronegativity and non-metallic character increase.

Down a group, atomic radius increases and ionisation energy decreases because the outer electron is farther and shielded.

Alkali metals (Group 1) are soft, highly reactive, form +1 ions; reactivity increases down the group.

Halogens (Group 17) form −1 ions; reactivity decreases down the group as electronegativity falls.

Noble gases (Group 18) have stable octets and very low reactivity; ionisation energy is highest in each period.

Metals occupy the left and centre, non-metals the upper right; metalloids such as Si and Ge lie along the dividing line.

Anomalies: noble gas radii are measured as van der Waals radii, so they appear larger than expected across a period.

Ionic bond forms by transfer of electrons from a metal to a non-metal; lattice energy and high melting point result.

Covalent bond forms by sharing electrons between non-metals; molecules are usually poor conductors.

Octet rule: atoms gain, lose or share electrons to reach eight in the valence shell; H and He follow the duet rule.

Lewis structure shows valence electrons as dots; double and triple bonds share four and six electrons.

Polar covalent bond arises when electronegativity differs; unequal sharing gives partial charges, as in HCl.

Electrovalent compounds conduct electricity when molten or dissolved but not when solid, because ions are fixed in the lattice.

Coordinate or dative bond: one atom donates both shared electrons, as in NH₄⁺ or H₃O⁺.

Metallic bonding: positive ion lattice surrounded by delocalised electrons, explaining conductivity and malleability.

Bond strength order is generally ionic lattice > covalent network > metallic > hydrogen bonding > van der Waals forces.

Arrhenius acid gives H⁺ in water; base gives OH⁻; Brønsted–Lowry acid is a proton donor and base a proton acceptor.

pH = −log[H⁺]; pH below 7 is acidic, 7 neutral, above 7 basic at 25 °C; each unit is a tenfold change.

Neutralisation: acid + base → salt + water; acid + metal → salt + hydrogen gas.

Acid + metal carbonate or bicarbonate → salt + water + CO₂; the gas turns limewater milky.

Indicators: litmus red in acid, blue in base; phenolphthalein colourless in acid, pink in base; methyl orange red in acid, yellow in base.

Strong acids (HCl, H₂SO₄, HNO₃) ionise completely; weak acids (CH₃COOH, H₂CO₃) ionise partially.

Common salt NaCl is neutral; washing soda Na₂CO₃·10H₂O and baking soda NaHCO₃ are basic salts used in industry and cooking.

Plaster of Paris is CaSO₄·½H₂O, made by heating gypsum to about 373 K; it sets hard with water.

Water of crystallisation gives hydrated salts their shape and colour, as in blue CuSO₄·5H₂O; heating removes it and turns it white.

Carbon is tetravalent and forms strong covalent bonds with itself (catenation) and with H, O, N, S, giving millions of compounds.

Saturated hydrocarbons contain only single bonds (alkanes, CₙH₂ₙ₊₂); unsaturated ones have double (alkenes) or triple (alkynes) bonds.

Homologous series differ by one CH₂ unit; members share general formula and similar chemical properties with graded physical properties.

Functional groups: alcohol –OH, aldehyde –CHO, ketone –CO–, carboxylic acid –COOH, ester –COO–; they decide chemical behaviour.

Ethanol is made by fermentation of sugar with yeast; oxidation gives ethanoic acid (vinegar).

Esterification: carboxylic acid + alcohol in acid catalyst gives ester with a sweet smell, used in perfumes and flavours.

Soaps are sodium or potassium salts of long-chain fatty acids; they form micelles and clean by emulsifying oil in water.

Detergents work in hard water because their calcium salts are soluble, unlike soap scum.

Addition reactions occur at double and triple bonds; substitution occurs in alkanes, as in chlorination of methane in sunlight.

Cell theory: all living things are made of cells, the cell is the basic unit of life, and new cells arise from existing cells.

Prokaryotic cells lack a membrane-bound nucleus and organelles; eukaryotic cells have a true nucleus and membrane-bound organelles.

Plant cells have a cellulose cell wall, chloroplasts and a large central vacuole; animal cells lack these.

Mitochondria are the site of aerobic respiration and ATP production; they are called the powerhouse of the cell.

Ribosomes synthesise proteins; the rough endoplasmic reticulum transports them, while smooth ER makes lipids.

Golgi apparatus modifies, packages and secretes proteins and forms lysosomes, the digestive bags of the cell.

Nucleus contains chromatin (DNA + histone) and the nucleolus, which makes ribosomal RNA.

Plasma membrane is selectively permeable, described by the fluid mosaic model with proteins floating in a lipid bilayer.

Osmosis moves water across a semipermeable membrane from low to high solute concentration; plasmolysis occurs in a hypertonic solution.

Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ in chloroplasts; light reactions make ATP and NADPH, the Calvin cycle fixes CO₂.

Chlorophyll absorbs mainly blue-violet and red light, reflecting green; stomata allow CO₂ entry and water loss.

Transpiration pull, root pressure and capillary action move water up the xylem; phloem translocates food.

Respiration: glycolysis in cytoplasm, Krebs cycle in mitochondria, and the electron transport chain yields most ATP.

Human digestion: starch begins in the mouth (salivary amylase), protein in the stomach (pepsin), fats in the small intestine (lipase, bile).

Blood: plasma, RBCs with haemoglobin for oxygen transport, WBCs for immunity, platelets for clotting.

Nephron is the functional unit of the kidney; filtration in the glomerulus and reabsorption in the tubule form urine.

Neuron transmits impulses; the synapse uses neurotransmitters; reflex action is a rapid involuntary response through the spinal cord.

Hormones: insulin from the pancreas lowers blood glucose; thyroxine from the thyroid controls metabolic rate and growth.

Mendel's law of segregation: the two alleles of a gene separate during gamete formation, so each gamete carries one.

Law of independent assortment applies to genes on different chromosomes; dihybrid ratio is 9:3:3:1.

Monohybrid cross of Tt × Tt gives 3:1 phenotype and 1:2:1 genotype; test cross with tt reveals a genotype.

Dominant allele masks the recessive one in heterozygotes; codominance and incomplete dominance give intermediate or dual phenotypes.

Genotype is the allele combination; phenotype is the observable trait; homozygous means identical alleles.

Sex determination in humans is XY: the father's sperm determines the child's sex; the mother contributes X only.

DNA is a double helix of nucleotides (A, T, G, C) with A–T and G–C base pairing; genes are DNA segments coding for proteins.

Evolution evidence: fossils, homologous organs, embryology and molecular similarity; Darwin proposed natural selection.

Speciation occurs when populations become reproductively isolated; variation and selection drive adaptation.

Ecosystem components: producers, consumers, decomposers plus abiotic factors such as light, water and soil.

Food chain transfers energy; only about 10 % passes to the next trophic level, so food chains rarely exceed four or five links.

Ozone layer in the stratosphere absorbs ultraviolet radiation; CFCs destroy ozone, causing the ozone hole.

Greenhouse gases (CO₂, CH₄, N₂O, water vapour) trap infrared radiation, causing global warming and climate change.

Acid rain forms when SO₂ and NOₓ dissolve in rain to give sulphuric and nitric acids; pH below 5.6 damages soil and buildings.

Biodegradable waste is broken down by microbes; non-biodegradable plastics persist and cause biomagnification of pollutants.

Conservation: in-situ protection in national parks and sanctuaries, ex-situ protection in seed banks and zoos.

Biodiversity hotspots have high species richness and endemism under threat; India has hotspots such as the Western Ghats.

Sustainable practices: reduce, reuse, recycle; rainwater harvesting and renewable energy reduce resource depletion.

Pathogens include bacteria, viruses, protozoa and fungi; each disease has a specific causative agent and mode of transmission.

Malaria is caused by Plasmodium and spread by the female Anopheles mosquito; dengue is spread by Aedes aegypti.

Tuberculosis is caused by Mycobacterium tuberculosis and spreads through air droplets; BCG is a preventive vaccine.

Immunity: innate defence is non-specific; acquired immunity involves antibodies and memory cells after infection or vaccination.

Vaccines contain weakened or killed pathogens or antigens, prompting antibody production without causing disease.

Personal hygiene: handwashing with soap, safe drinking water, and covered food prevent diarrhoeal diseases such as cholera.

Balanced diet supplies energy and nutrients; deficiency causes anaemia (iron), goitre (iodine), night blindness (vitamin A).

Lifestyle diseases such as diabetes, obesity and hypertension are linked to diet, inactivity and tobacco or alcohol use.

First aid: wash wounds, control bleeding with pressure, and for snake bite immobilise the limb and reach hospital quickly.

Electric motor converts electrical energy to mechanical energy using the force on a current-carrying coil in a magnetic field.

Electric generator converts mechanical energy to electrical energy by electromagnetic induction; AC reverses direction each half cycle.

Transformer changes AC voltage: step-up raises voltage and lowers current; it works only on AC, not DC.

Semiconductors such as silicon and germanium conduct better when doped; n-type has electron carriers, p-type has hole carriers.

A diode allows current in one direction only; a p-n junction rectifies AC to DC.

LASER produces a coherent, monochromatic, highly directional beam; used in surgery, cutting and communication.

Fibre optics transmits light by total internal reflection, carrying data with low loss.

Biogas from anaerobic digestion of cow dung and waste is mostly methane and is a renewable fuel.

Nuclear fission of uranium releases energy in a reactor; controlled chain reaction needs a moderator and control rods.

Scientific method: observation, hypothesis, controlled experiment, data analysis, conclusion; a hypothesis must be testable and falsifiable.

Independent variable is changed, dependent variable is measured, and controlled variables are kept constant.

SI base units: metre, kilogram, second, ampere, kelvin, mole, candela; derived units include newton, joule, watt, pascal.

Least count is the smallest value an instrument can measure; vernier callipers read 0.1 mm and screw gauge 0.01 mm.

Zero error must be added or subtracted from readings; parallax error is avoided by viewing the scale perpendicularly.

Significant figures reflect precision; in calculations, the result keeps the least number of significant figures in the data.

Density = mass/volume; measure mass by balance and volume by displacement for irregular solids.

A simple pendulum's time period T = 2π√(L/g); time many oscillations and divide to reduce timing error.

Graph rules: plot the independent variable on the x-axis, label axes with units, and draw a line of best fit rather than joining every point.