Physics
Right-Hand Thumb Rule — Thumb = current direction, curled fingers = magnetic field lines. For force on conductor: First finger = Field, seCond = Current, thuMb = Motion (Fleming's left hand).
VIBGYOR for EM Spectrum — Radio, Micro, Infrared, Visible, Ultra, X-ray, Gamma in increasing frequency/energy order. Remember: "Raging Martians Invaded Venus Using X-ray Guns."
Kirchhoff's Rules Trick — Junction rule: current IN = current OUT (like water pipes). Loop rule: voltage rises (–→+) add positive, drops (+→–) subtract. Battery gives rise, resistor gives drop.
Projectile Range Formula — Maximum range at 45°; complementary angles (30°-60°, 15°-75°) give same range. Formula: R = u²sin(2θ)/g.
Lens/Mirror Sign Convention — Distances measured FROM optical center/pole. LEFT is negative, RIGHT is positive. Upward heights positive, downward negative. Real image has negative v.
Escape Velocity = √2 × Orbital — If orbital velocity is v, escape velocity = v√2. At Earth: orbital ≈7.9 km/s, escape ≈11.2 km/s. Factor of √2 always applies.
Bohr Model: Energy ∝ 1/n² — Ground state n=1 has –13.6 eV. For nth level: E = –13.6/n². First excitation (n=2) = –3.4 eV. Radius ∝ n².
Alternating Current XL vs XC — Inductive reactance XL = 2πfL (increases with frequency). Capacitive XC = 1/(2πfC) (decreases with frequency). At resonance: XL = XC.
Photoelectric Effect Threshold — Einstein equation: KE_max = hf – φ. If frequency < threshold, NO electrons emitted regardless of intensity. Higher intensity = more electrons, NOT more energy per electron.
Nuclear Decay Memory: APE — Alpha decay: A drops by 4, Z drops by 2. Beta⁻ decay: A same, Z increases by 1. Positron/Beta⁺: A same, Z decreases by 1.
Ampere's Law Direction — Curl right-hand fingers in current loop direction; thumb points to magnetic field's North pole. For solenoid: fingers follow coil current, thumb shows N-pole.
Equipotential Surface Rule — Electric field ALWAYS perpendicular to equipotential surfaces. No work done moving charge along equipotential. Surfaces never intersect.
Chemistry
HONC 1234 Rule — Hydrogen forms 1 bond, Oxygen 2, Nitrogen 3, Carbon 4 in organic molecules. Quick check for structure validity in hydrocarbons and functional groups.
Le Chatelier's Principle Shortcut — Stress applied, equilibrium shifts to relieve it. Increase pressure → fewer moles side. Increase temperature → endothermic direction. Add reactant → forward shift.
Hybridization = ½(V+M–C+A) — V = valence electrons of central atom, M = monovalent atoms, C = cationic charge, A = anionic charge. Result: 2=sp, 3=sp², 4=sp³, 5=sp³d, 6=sp³d².