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

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

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

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

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)

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

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: 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

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)

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)

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)

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)

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 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)

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