Science — Class 10 to 12 Complete Guide

Before you start: Class 9 science fundamentals (basic atomic structure, simple motion) are assumed — this guide builds from Class 10 onward.

This guide covers CBSE/ICSE Science from Class 10 through Class 12, including Physics, Chemistry, and Biology — with clear explanations, key formulas, and exam-focused summaries.

Why This Exists (The Hook)

Physics, Chemistry, and Biology look like three unrelated subjects on a timetable, but they're really one continuous story told at different scales — Physics explains how energy and forces behave, Chemistry explains how atoms use that physics to bond into molecules, and Biology explains how those molecules organize into living systems that use energy (respiration), transform it (photosynthesis), and pass information forward (genetics). A single equation — E=mc² territory aside — like the ATP yield of respiration only makes sense once you already know what a chemical bond is, which only makes sense once you know what an electron is.

Analogy — Think of Science's three subjects like zoom levels on the same map, not three separate maps. Physics is the widest zoom — forces, energy, motion, the rules everything else obeys. Chemistry zooms in to how atoms use those rules to combine into molecules. Biology zooms in further to how those molecules organize into cells and organisms that are, underneath everything, still just obeying the same physics you started with. Zooming between them is why "why does rusting release heat" (Chemistry) traces back to "what is an exothermic reaction" (Physics-adjacent thermodynamics), which is why concepts genuinely build on each other across the three subjects.

Try it (2 minutes) — Reason through why aerobic respiration produces far more ATP (38) than anaerobic respiration/fermentation (2), without looking anything up: aerobic respiration's full equation is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP; anaerobic fermentation is C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + 2 ATP. Both start with the same glucose molecule. What's present on the left side of the aerobic equation that's completely absent from the anaerobic one — and given that oxygen is what allows a cell to fully break down glucose (releasing far more of the energy stored in its bonds) instead of only partially breaking it down, why would that explain the roughly 19x difference in ATP yield?

Class 10 Science

Physics — Electricity and Circuits

Electric current: Flow of charge per unit time
  I = Q/t  (Ampere = Coulomb/second)

Ohm's Law: V = IR  (Voltage = Current × Resistance)
  V in Volts, I in Amperes, R in Ohms

Resistance of a wire:
  R = ρL/A  (ρ = resistivity, L = length, A = cross-section area)
  Longer wire → more resistance
  Thicker wire → less resistance

Series circuit:
  Same current through all components
  Rₜₒₜₐₗ = R₁ + R₂ + R₃
  Vₜₒₜₐₗ = V₁ + V₂ + V₃

Parallel circuit:
  Same voltage across all components
  1/Rₜₒₜₐₗ = 1/R₁ + 1/R₂ + 1/R₃
  Iₜₒₜₐₗ = I₁ + I₂ + I₃
  
  Note: Total parallel resistance is LESS than smallest individual resistance

Power: P = VI = I²R = V²/R  (Watts)
Electric energy: E = Pt = VIt  (Joules or kWh)
1 kWh (unit of electricity) = 1000 W × 3600 s = 3.6 × 10⁶ J

Physics — Light

Reflection laws:
  1. Angle of incidence = Angle of reflection
  2. Incident ray, normal, reflected ray are coplanar

Mirror formula: 1/v + 1/u = 1/f
Magnification: m = -v/u = h_image/h_object

Concave mirror: Converging, focus in front
  Real image: Object beyond focus (inverted, varies in size)
  Virtual image: Object between focus and mirror (erect, magnified)
  Uses: Shaving mirrors, torches, dentist mirrors, satellite dishes

Convex mirror: Diverging, focus behind mirror
  Always virtual, erect, diminished image
  Uses: Rear-view mirrors, security mirrors in shops

Refraction: Light bending when passing between media
  Snell's Law: n₁ sin θ₁ = n₂ sin θ₂
  Refractive index: n = speed of light in vacuum / speed in medium
  n = c/v  (n water ≈ 1.33, n glass ≈ 1.5)

Lens formula: 1/v - 1/u = 1/f
  Convex lens: Converging, real and virtual images possible
  Concave lens: Diverging, always virtual, erect, diminished image

Power of lens: P = 1/f(metres)  unit = Dioptre
  +ve = convex, -ve = concave

Chemistry — Chemical Reactions

Types of reactions:
  Combination: A + B → AB  (e.g. 2H₂ + O₂ → 2H₂O)
  Decomposition: AB → A + B  (e.g. 2H₂O₂ → 2H₂O + O₂)
  Displacement: A + BC → AC + B  (more reactive displaces less reactive)
  Double displacement: AB + CD → AD + CB  (exchange partners)
  Redox: Oxidation + Reduction occurring simultaneously

Balancing chemical equations:
  Apply law of conservation of mass
  Same number of each atom on both sides
  
  Unbalanced: Fe + Cl₂ → FeCl₃
  Balanced: 2Fe + 3Cl₂ → 2FeCl₃

Acids, Bases, and Salts:
  Acid: Produces H⁺ ions in solution. pH < 7
  Base: Produces OH⁻ ions in solution. pH > 7
  Neutral: pH = 7  (pure water)
  
  Neutralisation: Acid + Base → Salt + Water
  HCl + NaOH → NaCl + H₂O
  
  Indicators: Litmus, phenolphthalein, methyl orange
  Red litmus → blue = base; Blue litmus → red = acid

Chemistry — Metals and Non-Metals

Properties of metals:
  Lustrous, malleable, ductile, good conductors, high melting point
  
Reactivity series (memorise from top to bottom):
  K, Na, Ca, Mg, Al, Zn, Fe, Ni, Sn, Pb, H, Cu, Hg, Ag, Au, Pt

  More reactive = above H → displaces H from acid
  Less reactive = below H → does not react with dilute acids

Extraction of metals:
  Highly reactive (K, Na, Ca, Mg, Al): Electrolytic reduction
  Moderately reactive (Fe, Zn, Pb): Reduction with carbon/coke
  Low reactivity (Cu, Hg, Ag): Reduction by heating alone

Corrosion: Metal reacts with environment
  Rusting of iron: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ → Fe₂O₃ (rust)
  Prevention: Painting, galvanising, alloying, electroplating

Biology — Life Processes

Nutrition:
  Autotrophs: Make their own food (plants — photosynthesis)
  Heterotrophs: Depend on others (animals, fungi)
  
  Photosynthesis: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
  Location: Chloroplasts (green organelle in plant cells)
  Light reactions (thylakoid): Light energy → chemical energy (ATP)
  Dark reactions (stroma): CO₂ → glucose using ATP

Respiration:
  Aerobic: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP
  Anaerobic (fermentation in yeast): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + 2 ATP
  Anaerobic (in muscle): C₆H₁₂O₆ → 2 lactic acid + 2 ATP (causes muscle cramps)

Transpiration: Water loss from plant leaves through stomata
  Pulls water up from roots through xylem
  
Transport in humans:
  Heart: 4 chambers — 2 atria (receive), 2 ventricles (pump)
  Right side: Deoxygenated blood → lungs
  Left side: Oxygenated blood → body
  Double circulation: 2 rounds for blood — pulmonary (lungs) + systemic (body)

Class 11 Physics

Kinematics

Uniform motion: v = constant, a = 0
  s = vt

Uniformly accelerated: a = constant
  v = u + at
  s = ut + ½at²
  v² = u² + 2as

Projectile motion (horizontal throw or at angle):
  Horizontal: x = u cosθ · t  (constant velocity)
  Vertical: y = u sinθ · t - ½gt²  (accelerated by gravity)
  
  Time of flight: T = 2u sinθ/g
  Range: R = u² sin 2θ/g  (maximum range at 45°)
  Maximum height: H = u² sin²θ/2g

Newton's Laws of Motion

First law (Inertia): Object stays at rest or constant velocity unless acted on by net force

Second law: F = ma  (Newtons = kg × m/s²)
  Net force = mass × acceleration
  
Third law: For every action, there is equal and opposite reaction

Momentum: p = mv
  Impulse = Force × time = change in momentum
  
Conservation of momentum: 
  No external force → total momentum constant
  m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

Friction:
  Static: f ≤ μₛN  (opposes tendency to move)
  Kinetic: f = μₖN  (opposes motion)
  μₛ > μₖ always
  
  Smooth incline: a = g sinθ
  Rough incline: a = g(sinθ - μ cosθ)

Work, Energy, Power

Work: W = F · d · cosθ
  Positive work: Force in direction of motion
  Negative work: Force opposing motion (friction)
  Zero work: Perpendicular force (circular motion, normal force)

Kinetic energy: KE = ½mv²
Potential energy (gravitational): PE = mgh

Work-Energy theorem: Net work = Change in KE

Conservation of energy: Total mechanical energy = constant (no friction)
  KE + PE = constant
  ½mv² + mgh = constant
  
Power: P = W/t = Fv  (Watts = J/s)
  1 HP = 746 W

Elastic collision: Both KE and momentum conserved
Inelastic collision: Only momentum conserved (KE not conserved)
Perfectly inelastic: Objects stick together after collision

Class 12 Physics

Electrostatics

Coulomb's law: F = kq₁q₂/r²  (k = 9×10⁹ N·m²/C²)

Electric field: E = F/q₀ = kq/r²  (direction from + to -)
  Electric field lines: From + to -, don't cross, close spacing = strong field

Electric potential: V = kq/r  (Scalar quantity)
  V = 0 at infinity, negative near negative charges
  Work done: W = q(V₁ - V₂)
  
Capacitors: Stores charge
  C = Q/V = ε₀A/d  (parallel plate)
  Series: 1/C = 1/C₁ + 1/C₂  (equivalent capacitance decreases)
  Parallel: C = C₁ + C₂  (equivalent capacitance increases)
  Energy stored: U = ½CV² = Q²/2C
  With dielectric: C = κε₀A/d  (κ = dielectric constant, always > 1)

Electromagnetic Induction

Faraday's law: EMF = -dΦ/dt  (rate of change of magnetic flux)
  Φ = B·A·cosθ  (magnetic flux)

Lenz's law: Induced current opposes the change that caused it
  (Conservation of energy)

Self-inductance: EMF = -L(dI/dt)
  L = μ₀n²V  (for solenoid)
  
Mutual inductance: EMF₂ = -M(dI₁/dt)

Transformer:
  V₁/V₂ = N₁/N₂ = I₂/I₁  (ideal transformer)
  Step-up: N₂ > N₁, V₂ > V₁
  Step-down: N₂ < N₁, V₂ < V₁
  Power loss: P = I²R (in transmission lines)
  Solution: Transmit at high voltage, low current (step-up transformer)

Class 11-12 Chemistry

Chemical Bonding

Ionic bond: Metal + Non-metal → electron transfer
  NaCl: Na loses 1e⁻ → Na⁺, Cl gains 1e⁻ → Cl⁻
  Properties: High MP/BP, conducts when dissolved, brittle

Covalent bond: Non-metal + Non-metal → electron sharing
  H₂O: O shares 2 electrons with 2 H atoms
  Properties: Low MP/BP, usually non-conductors

VSEPR Theory — molecular geometry:
  2 bond pairs: Linear (CO₂)
  3 bond pairs: Trigonal planar (BF₃)
  4 bond pairs: Tetrahedral (CH₄)
  3 bond + 1 lone: Pyramidal (NH₃)
  2 bond + 2 lone: Bent/angular (H₂O)
  
Hybridisation:
  sp: Linear (2 bond directions), 180°  (BeCl₂, CO₂, alkynes)
  sp²: Trigonal planar, 120°  (BF₃, alkenes, benzene)
  sp³: Tetrahedral, 109.5°  (CH₄, NH₃, H₂O, alkanes)

Organic Chemistry — Basics

Carbon is special because:
  Forms 4 bonds, can bond to itself extensively
  Single (C-C), Double (C=C), Triple (C≡C) bonds

Homologous series — families of organic compounds:
  Alkanes: CₙH₂ₙ₊₂  (methane CH₄, ethane C₂H₆, propane C₃H₈)
  Alkenes: CₙH₂ₙ   (ethene C₂H₄, propene C₃H₆)
  Alkynes: CₙH₂ₙ₋₂  (ethyne C₂H₂)
  Alkanols: CₙH₂ₙ₊₁OH  (methanol, ethanol)
  Alkanoic acids: CₙH₂ₙ₊₁COOH  (methanoic acid, ethanoic acid/vinegar)

Functional groups determine properties:
  -OH (hydroxyl): Alcohol  
  -COOH (carboxyl): Carboxylic acid (acidic)
  -CHO (aldehyde): Aldehyde
  -CO- (ketone): Ketone
  -NH₂ (amino): Amine (basic)

Class 12 Biology

Genetics — Mendel's Laws

Gregor Mendel's Laws:
  1. Law of Dominance: Dominant allele expressed over recessive
  2. Law of Segregation: Allele pairs separate during gamete formation
  3. Law of Independent Assortment: Different trait pairs assort independently

Terminology:
  Gene: Unit of heredity
  Allele: Variant form of a gene (dominant A vs recessive a)
  Genotype: Genetic makeup (AA, Aa, aa)
  Phenotype: Observable characteristic
  Homozygous: Same alleles (AA or aa)
  Heterozygous: Different alleles (Aa)
  
Monohybrid cross (Aa × Aa):
  Offspring: 1AA : 2Aa : 1aa
  Phenotype ratio: 3 dominant : 1 recessive

Dihybrid cross (AaBb × AaBb):
  Phenotype ratio: 9:3:3:1
  (Both dominant : first only : second only : both recessive)

Sex determination in humans:
  Males: XY, Females: XX
  Mother always gives X, Father gives X (girl) or Y (boy)
  All sex-linked diseases traced through X chromosome (haemophilia, colour blindness)

DNA and Molecular Genetics

DNA structure:
  Double helix (Watson and Crick, 1953)
  Nucleotide = phosphate + sugar + nitrogenous base
  Bases: Adenine (A) pairs with Thymine (T)
         Guanine (G) pairs with Cytosine (C)
  
  A-T bond: 2 hydrogen bonds
  G-C bond: 3 hydrogen bonds (more stable, higher G-C = higher melting point)

Central Dogma of Molecular Biology:
  DNA → (Transcription) → mRNA → (Translation) → Protein
  
  Transcription: DNA → mRNA (in nucleus)
  Translation: mRNA → Protein (at ribosomes)
  
  Codon: 3 bases in mRNA code for 1 amino acid
  61 codons → 20 amino acids (genetic code is degenerate)
  3 stop codons: UAA, UAG, UGA
  Start codon: AUG (also codes for Methionine)

Exam Strategy

CBSE pattern for Science (Class 10):
  Section A: 16 MCQ (1 mark)
  Section B: 5 short answer (2 marks)
  Section C: 7 short answer (3 marks)
  Section D: 3 long answer (5 marks)
  Section E: 3 case-based (4 marks)

Class 12 Physics strategy:
  Most students lose marks in calculations — show every step
  Derivations: Write the complete derivation, not just final answer
  Diagrams: Always draw and label circuit diagrams, ray diagrams
  Units: Always include units with numerical answers

Key topics by marks weight (Class 12):
  Physics: Electrostatics 8m, Current Electricity 7m, Magnetism 8m, Optics 10m
  Chemistry: Solutions 5m, Electrochemistry 5m, Chemical Kinetics 5m, Organic 28m
  Biology: Genetics 15m, Reproduction 14m, Ecology 14m, Biotechnology 10m

Physics — Optics

10 marks -- highest single Physics topic in Class 12

Chemistry — Organic

28 marks -- by far the largest Chemistry weight

Biology — Genetics

15 marks -- the largest single Biology topic

Biology — Reproduction / Ecology

14 marks each -- next largest Biology topics

Science — Overview