Physics
Right-hand thumb rule — For current-carrying conductor: thumb = motion/current direction, curled fingers = magnetic field direction. For solenoid: curl fingers in current direction, thumb shows N-pole.
ROYGBIV — Red, Orange, Yellow, Green, Blue, Indigo, Violet—remembering spectrum order and visible light wavelengths from longest (red ~700nm) to shortest (violet ~400nm).
SALT for image — Size, Attitude (erect/inverted), Location, Type (real/virtual). Systematically analyze ray diagrams and mirror/lens image formation in all numerical problems.
v² - u² = 2as shortcut — When time unknown, use this equation. If final velocity = 0 (object stops), then u² = 2as directly gives initial velocity from distance and acceleration.
Ohm's V=IR triangle — Draw triangle: V on top, I and R at bottom. Cover what you need; remaining two show the formula (V=IR, I=V/R, R=V/I).
G vs g confusion — Capital G (6.67×10⁻¹¹) = universal gravitational constant, never changes. Small g (9.8 m/s²) = acceleration due to gravity, varies with height and planet.
Right-hand palm rule — Stretch thumb, first finger, second finger perpendicular. First finger = magnetic field, thumb = motion/force, second finger = induced current direction (Fleming's rule for motor).
Chemistry
OIL RIG — Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). Identifies oxidizing and reducing agents instantly in redox equations.
PANL for subatomic — Proton (+), Alpha particle (2p+2n), Neutron (neutral), Lithium nucleus (same as alpha). Remember charge and mass for Structure of the Atom numericals.
Sodium compounds pH mnemonic — Common sodium salts: Na₂CO₃ (washing soda) basic pH~11, NaHCO₃ (baking soda) weakly basic pH~8, NaCl neutral pH~7. Chlorides of strong bases = neutral.
Valency trick by 8-rule — Groups 1-4: valency = group number. Groups 5-7: valency = 8 minus group number. So Group 15 nitrogen = 8-5 = 3 valency.
Homologous series CₙH₂ₙ₊₂ — Alkanes: saturated, single bonds. Each -CH₂- added increases molecular mass by 14. Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈)—systematic progression for carbon compounds.
Activity series KCaNavyMgAlZincIronLeadHydrogenCopperSilverGold — "King Can Navigate My Aircraft Zigzag In London Heading Carefully Skyward Gloriously." More reactive metals displace less reactive from salt solutions.
Lanthanides Actinides rows — Lanthanides = elements 58-71 (Ce to Lu), Actinides = 90-103 (Th to Lr). Both go in separate rows below main periodic table, f-block elements.
Biology
MR CHEN for life processes — Movement, Respiration, Control & Coordination, Health, Excretion, Nutrition. Six characteristics distinguishing living from non-living things.
PMAT mitosis stages — Prophase, Metaphase, Anaphase, Telophase. Chromosome behavior: Prophase = condense, Metaphase = middle align, Anaphase = apart move, Telophase = two nuclei form.
Cranial nerves — 12 pairs in humans: I-Olfactory (smell), II-Optic (vision), III-Oculomotor (eye movement). Remember sensory (S), motor (M), or both (B) functions for each nerve.
XY-XX sex determination — Male = XY (heterogametic, produces two gamete types), Female = XX (homogametic, one gamete type). Punnet square: 50% probability for male/female offspring always.
Stomata opening — Guard cells swell → stomata open (day/photosynthesis). Guard cells shrink → stomata close (night/water conservation). Turgor pressure drives this diurnal rhythm mechanism.
Food chain 10% rule — Only 10% energy transfers to next trophic level. Producer (100%) → Primary consumer (10%) → Secondary consumer (1%) → Tertiary consumer (0.1%). Energy pyramids always upright.
Reasoning and Aptitude
BODMAS order — Brackets, Of (powers/roots), Division, Multiplication, Addition, Subtraction. Left-to-right for equal priority operations. Common trap: 2+3×4 = 2+12 = 14, NOT 20.
Venn diagram shortcuts — Only A = Total A - (A∩B). Neither A nor B = Total - (A + B - A∩B). These formulas solve 90% set theory Olympiad problems instantly.
Clock angle formula — |30H - 5.5M| degrees, where H=hours, M=minutes. At 3:15, angle = |30(3) - 5.5(15)| = |90-82.5| = 7.5°. Works for all hour-minute combinations.
Divisibility by 11 — Alternating digit sum: subtract odd-position digits from even-position. If result = 0 or multiple of 11, number divisible by 11. Example: 121→(2)-(1+1)=0, divisible.
Mirror/Water image — Mirror (vertical): left↔right swap only. Water (horizontal): top↔bottom flip only. Letters like A, H, T unchanged in mirror; B, C, D change appearance completely.